Added the resource economy, its works and their icons

- Five resources (energy, steel, food, luxury, high-tech) with per-city stores, a world market, delivery and material upkeep. - Resource-producing tile works built outside cities; every nation opens with the works its economy needs. - Real game-icons.net art replacing the dummy icons for the new resources and works, with the credits updated.
2026-09-22 05:27:11 +02:00
parent 9690c68ced
commit e7ee5dbf0e
92 changed files with 7994 additions and 911 deletions
@@ -98,15 +98,154 @@ simplification worth revisiting. Anything unticked is still open.
      enemy walking on it), coastal cannon (auto-fires on warships).
 - [x] Embark / disembark orders wired on server and client, with a cargo readout
      in the unit panel.
+- [ ] Easy and ergonomic way to split unit stacks.
+- [ ] Give stacks with range units a dedicated button to perform ranged attacks,
+      right-clicking will now ONLY move (obviously triggers a battle when moving on the same tile)

 ## 6. Content and tuning

 - [x] Market and Bank base cost reduced tenfold (500k and 1M).

+## 7. Resources
+
+- [x] Add the following resource groups:
+  - [x] Energy. Uses the electric icon. In kWh, MWh, GWh, TWh.
+  - [x] Steel. Uses the I-beam icon. In tonnes.
+  - [x] Food. Uses the apple icon. In tonnes.
+  - [x] Luxury. Uses the diamond icon. In carats.
+  - [x] High-tech. Uses the microchip icon. In units.
+
+* [x] Resources are stored on every tile that is either a city or a resource production building.
+  * [x] Cities and tiles automatically try to buy necessary resources from their neighbours, including non-hostile cities.
+  * [x] Energy produced by power plants cannot be stored.
+* [x] Keep track of resource prices in the global market.
+  * [x] Transporting resources costs additional money, used to automatically buy energy.
+* [~] Fossil fuels are abstracted into the transformative plants' money upkeep
+      rather than a stored fuel resource: the roadmap lists only the five
+      groups above, so coal, gas and oil are not separately tracked.
+* [~] Energy is modelled as a daily flow everywhere, so no city can bank it.
+      Only the other four groups have per-tile storage.
+
+
+### Delivering resources
+* [x] Delivering 1 tonne of resources over 1 tile requires 10 MWh by truck over roads, 50 MWh * tile movement cost without roads, 1 MWh by train, 50 kWh by ship.
+* [x] A delivery graph, revealed only in the economic map mode, is created.
+  * [x] The delivery graph is built
+* [~] A city always buys from the cheapest source: a nearby store whose
+      delivered price beats the market, or the global market itself. Market
+      buying uses a nominal two-tile road delivery.
+
+### Food
+* [x] Each person requires 1 kg of food per day. That's how much cities have to buy. Cities attempt to buy up to 130 % of their needs for the month.
+* [x] Producing 1 tonne of food requires 1 MWh of energy.
+
+### Energy
+* [x] Cities require energy to function. Add a new economic metric (not in the top though), kWh/€ of GDP. This determines the base energy consumption of cities.
+* [x] Electric energy is delivered instantly to the entire connected region when requested, at no cost.
+      Every country starts having each of their contiguous cities be connected.
+* [x] Without electric energy, cities and buildings attempt to buy energy that has to be delivered. 10 GWh of energy count as 1 tonne of material.
+* [x] Energy is needed to create all other resources
+
+### Steel
+* [x] Everything requires steel to be built.
+* [x] 20 MWh/tonne of steel at the steel mill
+* [x] Each inhabitant consumes 1 kg of steel per day.
+
+### Luxury
+* [x] Inhabitants require 0.01 ct of luxury per day. No building or military unit requires that.
+
+### High-tech
+* [x] Science buildings require high-tech so they can be built, and they will consume 1 unit of high-tech per tech point they produce.
+
+### Buildings
+* [x] New resource-producing buildings, built only _outside_ of cities:
+  * [x] Energy buildings:
+    * [x] Electricity buildings
+      * [x] Transformative plants: turn storable fossil fuels into electricity.
+        * [x] Coal power plant
+        * [x] Natural gas power plant
+        * [x] Oil power plant
+      * [x] Renewable energy plants: create a limited amount of electricity for free
+        * [x] Solar power plant
+        * [x] Geothermal plant
+        * [x] Wind turbines
+        * [x] Offshore wind turbines
+        * [x] Fusion power plant
+  * [x] Steel buildings:
+    * [x] Steel mill
+  * [x] Food buildings:
+    * [x] Food is automatically produced by tiles, in the same proportions as their population.
+  * [x] Luxury buildings:
+    * [x] Gold mine. 10 MWh/ct
+    * [x] Diamond mine. 5 MWh/ct
+  * [x] High-tech building:
+    * [x] Chip foundry.
+
+* [x] A dedicated resource panel in the nation modal: the Resources tab shows
+      each group's stores, daily need, upkeep and production beside the global
+      market's price and the world's supply and demand.
+* [x] Every nation opens with the resource works its economy needs, laid out
+      randomly from the world seed at map generation (converters first, then
+      enough power for each connected grid) so the opening economy covers its
+      people's, industry's and upkeep's needs. Works beside the transport
+      network get a one-tile road spur so their output can reach a city, and the
+      per-capita balance is re-derived afterwards so no nation starts richer
+      just because its land hosts more industry. Food is not covered by any
+      building, so a food-poor nation still buys on the market.
+* [x] A port also lifts its region's food output: 5% per adjacent sea tile per
+      level, on top of its GDP-per-capita bonus.
+
+### Upkeep and repairs
+* [x] Buildings, units, tile works and the transport network no longer cost
+      money to keep; they wear out in materials (steel, with high-tech for
+      advanced things) that the state buys from its stores and the market.
+      Money upkeep is now only propaganda campaigns.
+* [x] Construction spends materials as well as money (steel proportional to the
+      cost, high-tech for advanced items).
+* [x] Repairs cost materials: a razed city building level is rebuilt once paid
+      for, a damaged unit heals at a steel/high-tech cost, a damaged tile work
+      heals once its steel debt is cleared, and a tile with unpaid damage does
+      not recover its GDP.
+* [x] Infantry units carry 1,000 soldiers. Training one draws that many people
+      at random out of the region's population, and healing a damaged unit draws
+      replacement soldiers the same way. A unit's soldiers need double rations in
+      combat and triple while wounded and resting in one of their own cities.
+* [x] Supply applies to every land unit: it carries 50 days of food. At home, or
+      in foreign territory with a clear route (land or maritime) to an allied
+      city, it eats from the nearest such city and tops its pack up; cut off, the
+      days run down and then the soldiers start dying of starvation.
+* [x] Encirclement is local: a tile is encircled when enemy units hold every
+      land tile beside it and it has no working port. An encircled city or unit
+      loses its neighbours and the foreign market and eats its own reserves. A
+      port keeps its tile supplied unless enemy warships hold every sea tile
+      around the city (a blockade).
+* [x] Every naval city opens the game with a port. A working port on a city's
+      continent is the only link to other continents: without one, cities trade
+      over land on their own continent only and cannot use the foreign market
+      (nor can construction, upkeep, combat or unit supply draw on it).
+* [x] Every delivery runs on the transport network: roads and railways on land,
+      shipping lanes across water (which need a working port). There is no
+      off-road trucking, so a resource building or city off the network cannot be
+      bought from until it is linked, and a nation's market is reached along the
+      same roads and rails. Goods never cross the land of a nation you are at war
+      with.
+* [x] Guns and aircraft are cheap parked and costly to fire: air defense,
+      artillery and aircraft have little standing upkeep and spend munitions
+      (steel/high-tech) on every volley or sortie, with no shot when the
+      materials cannot be found.
+* [x] The fusion power plant is gated behind Fusion Power, a 500,000-point
+      technology.
+* [ ] A resource budget line in the national budget breakdown (the money spent
+      on upkeep, electric imports, goods and their transport is tracked by the
+      model but the actual spend is not yet its own row in the budget table; the
+      table currently forecasts upkeep at market prices).
+
+
 ## Open items

 - [ ] A dedicated structure hit-point model for cities and tile improvements
      (see the `[~]` note above).
 - [ ] Real art for the placeholder "dummy icon" SVGs: `icon_radar.svg`,
-      `icon_launch.svg`, `icon_fortifications.svg`, `icon_radar_tower.svg`,
-      `icon_coastal_cannon.svg`, `icon_road.svg`, `icon_railway.svg`.
+      `icon_coastal_cannon.svg`, `icon_chip_foundry.svg`,
+      `icon_geothermal_plant.svg`, `icon_offshore_wind_turbines.svg`,
+      `icon_wind_turbines.svg`.
@@ -0,0 +1,5 @@
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+  <rect x="8" y="8" width="496" height="496" rx="24" fill="#2b3550" stroke="#ffffff" stroke-width="12"/>
+  <text x="256" y="266" fill="#ffffff" font-family="sans-serif" font-size="40" font-weight="700" text-anchor="middle">dummy icon</text>
+  <text x="256" y="316" fill="#ffffff" font-family="sans-serif" font-size="40" font-weight="700" text-anchor="middle">chip foundry</text>
+</svg>
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+  <text x="256" y="316" fill="#ffffff" font-family="sans-serif" font-size="40" font-weight="700" text-anchor="middle">geothermal plant</text>
+</svg>
@@ -0,0 +1 @@
+<svg style="height: 512px; width: 512px;" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><path d="M2 2h508v508H2z" fill="#000000" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="2"></path><g class="" style="" transform="translate(0,0)"><path d="m169.5 38.97-2.406 9-4.313 16.093-34.936-9.344-3.375 12.53-26.75-7.156-4.845 18.03 26.78 7.19-2.874 10.655 34.94 9.343-12.25 45.718-34.94-9.343-3.31 12.282-26.75-7.157-4.845 18.062 26.75 7.156-2.906 10.907 34.936 9.344-12.53 46.69-34.907-9.345L78 240.75l-26.78-7.188-4.845 18.032 26.78 7.187-3.25 12.095 34.907 9.344-12 44.75-34.906-9.345-2.875 10.75-26.78-7.188-4.813 18.032 26.75 7.155-3.343 12.53 34.906 9.345-4.47 16.688-2.405 9.03 9.03 2.407 254.845 68.28 9.03 2.408 2.408-9.032 4.468-16.655 34.813 9.313 3.342-12.5 27.032 7.25 4.844-18.032-27.032-7.25 2.875-10.75-34.81-9.312 12-44.75 34.81 9.312 3.25-12.094 27.033 7.25 4.812-18.03-27.03-7.25 3-11.157-34.814-9.313 12.5-46.656 34.814 9.313L439 263.843l27.03 7.25 4.845-18.063-27.03-7.25 3.28-12.31-34.78-9.314 12.25-45.72 34.78 9.314 2.844-10.625 27.06 7.25 4.845-18.063-27.063-7.25 3.375-12.593-34.78-9.314 4.312-16.062 2.436-9.03-9.03-2.44-254.845-68.25-9.03-2.405zm13.188 22.874L419.53 125.28l-84.966 316.91L97.75 378.75l84.938-316.906zM375.28 132.78 305.5 393.22l-175.313-47-4.843 18.06 184.376 49.41 9 2.406 2.436-9.03 72.188-269.44-18.063-4.843z" fill="#c9c9c9" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="5"></path></g></svg>
@@ -0,0 +1 @@
+<svg style="height: 512px; width: 512px;" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><path d="M2 2h508v508H2z" fill="#000000" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="2"></path><g class="" style="" transform="translate(0,0)"><path d="m92.906 94.813 60.438 79.75 78.125-79.75H92.905zm189.25 0L359.25 173.5l58.688-78.688H282.155zm-25.344.843-84.718 86.47H341.53l-84.717-86.47zm177.907 7.906-58.626 78.563H494.53l-59.81-78.563zm-358.064.75-57.78 77.813h116.78l-59-77.813zm-58.5 96.5L226.562 429.22l-83.218-228.41H18.156zm145.063 0 93.593 256.844 93.593-256.844H163.22zm207.06 0L287.064 429.22l208.405-228.41H370.28z" fill="#50e3c2" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="5"></path></g></svg>
@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" style="height:512px;width:512px">
+  <rect x="8" y="8" width="496" height="496" rx="24" fill="#2b3550" stroke="#ffffff" stroke-width="12"/>
+  <text x="256" y="266" fill="#ffffff" font-family="sans-serif" font-size="40" font-weight="700" text-anchor="middle">dummy icon</text>
+  <text x="256" y="316" fill="#ffffff" font-family="sans-serif" font-size="40" font-weight="700" text-anchor="middle">offshore wind</text>
+</svg>
@@ -0,0 +1 @@
+<svg style="height: 512px; width: 512px;" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><g class="" style="" transform="translate(0,0)"><path d="M219.615 401.84h16v88.06h-16v-88.06zm219.94-271.6 21.83-13.18-21.82-13.16 16-19.8-25-4.88 8.25-24.12-25.19 4-.46-25.49-22.28 12.29-9.18-23.8-16.7 19.24-16.78-19.24-9.22 23.8-22.3-12.31-.46 25.49-25.19-4 8.25 24.12-25 4.88 16 19.8-21.83 13.18 21.83 13.14h33.41l29.29 76.34 12-13.76 16.74 19.24 9.17-23.76 22.3 12.31.46-25.49 25.19 4-8.28-24.18 25-4.88zm-254.55 46.31h-91l31 80.85h91zm108.25 0h-91l30.94 80.85h91zm-70.81 97.42h-91l30.94 80.85h91zm108.25 0h-91l30.94 80.85h91zm73.89 111.87h-262.22L50.615 146.2h262.1zm-19.69-15-43.31-112.87-37.28-97.42H70.785l80.47 210.27h233.68z" fill="#ffffff" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="5"></path></g></svg>
@@ -0,0 +1 @@
+<svg style="height: 512px; width: 512px;" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><path d="M2 2h508v508H2z" fill="#000000" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="2"></path><g class="" style="" transform="translate(0,0)"><path d="M39.557 19 323.44 273h149.003L188.56 19H39.558zM25 30.13v25.847L311 311.87v-25.846L25 30.13zm64 107.263v34.584L375 427.87v-84.843l-64-13.002L89 137.393zM77.555 185.89l-42.9 10.723 287.79 257.498 42.9-10.723L77.556 185.89zM25 212.13v23.847L311 491.87v-23.847L25 212.13zM329 291v21.973l64 16v126.054l-64 16V493h158v-21.973l-64-16V328.973l64-16V291H329zm112 135.865v14.108l21.88 5.47L441 426.865z" fill="#7c6a5b" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="5"></path></g></svg>
@@ -0,0 +1 @@
+<svg style="height: 512px; width: 512px;" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><g class="" style="" transform="translate(0,0)"><path d="M41 19v228h25.5c6.96 61.3 40.5 114.1 88.4 145.4l12.1 61.3-95.35-46.4a9.798 9.145 26.09 0 0-4.66-10.5 9.798 9.145 26.09 0 0-13.18 2.9 9.798 9.145 26.09 0 0 3.67 12.8 9.798 9.145 26.09 0 0 10.55-.1L144.5 496h216.6l33.4-22.3a8.636 11.2 54.07 0 0 .3 1.9 8.636 11.2 54.07 0 0 12.8 3.6 8.636 11.2 54.07 0 0 7.2-13 8.636 11.2 54.07 0 0-3.3-3.9l36.5-24.5-89.6 26.2 32.4-57.5-76.5 43.6 6.2-39.1c66.9-25.1 116.3-88.1 125-164H471V19h-30v155.4C420.1 88.03 345.3 23.87 256 23.87S91.93 87.95 71 174.2V19H41zm215 20.54c96.6 0 175.2 81.96 175.2 183.76 0 76.6-44.5 142-107.8 169.7l4.5-28.1L272 464c.1-47.1 1.5-159.3 34.6-204.7 40.7-16.6 68.4-52.4 68.4-93.3 0-56.3-52.6-103-119-103s-119 46.7-119 103c0 40.9 27.7 76.7 68.4 93.3 33.1 45.4 34.5 157.6 34.6 204.7l-51.8-128 .7 52.9-52.5-90 14.1 71.2c-42.3-33.6-69.66-86.7-69.66-146.8C80.84 121.5 159.4 39.54 256 39.54zM170.7 306.3a11.2 8.634 63.66 0 0-.9.1 11.2 8.634 63.66 0 0-5.7 11.9 11.2 8.634 63.66 0 0 11.6 9.4 11.2 8.634 63.66 0 0 5.8-12 11.2 8.634 63.66 0 0-10.8-9.4zm181 30.9a8.998 12.75 27.2 0 0-10.5 7.9 8.998 12.75 27.2 0 0 2.2 15.5 8.998 12.75 27.2 0 0 13.8-7.3 8.998 12.75 27.2 0 0-2.2-15.4 8.998 12.75 27.2 0 0-3.3-.7zM34.96 348.5a11.06 5.999 47.86 0 0-3.04 1 11.06 5.999 47.86 0 0 2.97 12.2 11.06 5.999 47.86 0 0 11.87 4.2 11.06 5.999 47.86 0 0-2.97-12.3 11.06 5.999 47.86 0 0-8.83-5.1zm363.14 26.3a6.561 14.62 40.07 0 0-12 7.8 6.561 14.62 40.07 0 0-4.4 15.4 6.561 14.62 40.07 0 0 14.5-7 6.561 14.62 40.07 0 0 4.4-15.4 6.561 14.62 40.07 0 0-2.5-.8zm81.2 59.7a7.525 16.82 50.66 0 0-15.5 7.8 7.525 16.82 50.66 0 0-5.7 15.7 7.525 16.82 50.66 0 0 18.7-7.1 7.525 16.82 50.66 0 0 5.7-15.7 7.525 16.82 50.66 0 0-3.2-.7zm-404.79 18a13.68 8.998 27.81 0 0-7.87 3.8 13.68 8.998 27.81 0 0 7.9 14.3 13.68 8.998 27.81 0 0 16.3-1.5 13.68 8.998 27.81 0 0-7.9-14.4 13.68 8.998 27.81 0 0-8.43-2.2z" fill="#ffffff" fill-opacity="1" stroke="#000000" stroke-opacity="1" stroke-width="5"></path></g></svg>
@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" style="height:512px;width:512px">
+  <rect x="8" y="8" width="496" height="496" rx="24" fill="#2b3550" stroke="#ffffff" stroke-width="12"/>
+  <text x="256" y="266" fill="#ffffff" font-family="sans-serif" font-size="40" font-weight="700" text-anchor="middle">dummy icon</text>
+  <text x="256" y="316" fill="#ffffff" font-family="sans-serif" font-size="40" font-weight="700" text-anchor="middle">wind turbines</text>
+</svg>
@@ -357,6 +357,24 @@ input:focus, select:focus { border-color: var(--accent); }
 /* A barrage the player is looking at stands out from the rest. */
 .target-line.target-selected, .target-ring.target-selected { opacity: 1; }

+/* The delivery graph, shown only in the economic map modes: a coloured line
+   per delivery leg and a dot on every storage node. */
+#layer-resources { pointer-events: none; }
+.resource-node {
+  position: absolute;
+  width: 10px;
+  height: 10px;
+  margin-left: -5px;
+  margin-top: -5px;
+  box-sizing: border-box;
+  border: 2px solid #ffffff;
+  border-radius: 50%;
+  background: #2b3550;
+  pointer-events: none;
+  box-shadow: 0 0 4px rgba(0, 0, 0, 0.8);
+}
+.resource-icon { vertical-align: middle; }
+
 /* Outlines the selected or inspected tile. The polygon is built in JS from the
   same warped hexagon as the terrain, so it follows the geography. */
 .tile-selection {
@@ -746,13 +764,21 @@ input:focus, select:focus { border-color: var(--accent); }
  padding: 12px 18px;
 }

-/* One button per buildable tile improvement, laid out in a wrapping row. */
+/* Tile improvements, grouped under a category heading. */
 .tile-improvement-actions {
  display: flex;
-  flex-wrap: wrap;
-  gap: 6px;
+  flex-direction: column;
+  gap: 8px;
  margin-top: 8px;
 }
+.improvement-group { display: flex; flex-direction: column; gap: 4px; }
+.improvement-category {
+  font-size: 10px;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+  color: var(--muted);
+}
+.improvement-row { display: flex; flex-wrap: wrap; gap: 6px; }
 .improvement-btn { font-size: 12px; }
 .improvement-btn.current { opacity: 0.6; }
 .improvement-btn.remove { border-color: rgba(242, 114, 114, 0.6); }
@@ -766,7 +792,32 @@ input:focus, select:focus { border-color: var(--accent); }
  padding: 5px 4px;
 }
 .improvement-icon { width: 40px; height: 40px; display: block; }
-.improvement-cost { font-size: 10px; color: var(--muted); font-variant-numeric: tabular-nums; }
+.improvement-cost {
+  display: flex;
+  flex-wrap: wrap;
+  justify-content: center;
+  align-items: center;
+  gap: 0 3px;
+  font-size: 10px;
+  color: var(--muted);
+  font-variant-numeric: tabular-nums;
+}
+.cost-res { display: inline-flex; align-items: center; gap: 2px; }
+.cost-icon { width: 12px; height: 12px; vertical-align: middle; }
+.cost-money { color: var(--muted); }
+
+/* The tile panel leads with what the tile actually produces. */
+#tile-production { margin: 4px 0 6px; display: flex; flex-direction: column; gap: 2px; }
+.tile-prod-row {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  font-size: 13px;
+  font-variant-numeric: tabular-nums;
+}
+.tile-prod-row .tile-prod-name { color: var(--muted); }
+.tile-prod-row .tile-prod-value { margin-left: auto; }
+.tile-prod-empty { font-size: 12px; color: var(--muted); }

 .info-section.hidden { display: none !important; }
 .info-title { font-size: 17px; font-weight: 600; margin-bottom: 4px; }
@@ -1228,6 +1279,16 @@ input:focus, select:focus { border-color: var(--accent); }
 .conflict-detail .conflict-line { font-size: 12px; color: var(--muted); }
 .conflict-detail .conflict-side { font-size: 13px; margin-top: 4px; }

+.economy-table { width: 100%; border-collapse: collapse; margin-top: 6px; }
+.economy-table th,
+.economy-table td { padding: 5px 8px; text-align: left; border-bottom: 1px solid rgba(255, 255, 255, 0.08); }
+.economy-table th { color: var(--muted); font-weight: 600; font-size: 11px; }
+.economy-table .numeric { text-align: right; font-variant-numeric: tabular-nums; }
+.central-bank-rate { display: flex; align-items: center; gap: 8px; margin: 8px 0; }
+.central-bank-rate label { color: var(--muted); }
+.central-bank-rate input { width: 90px; }
+.subhead { margin-top: 10px; color: var(--muted); font-weight: 600; }
+
 .diplomacy-table { width: 100%; border-collapse: collapse; }
 .diplomacy-table th,
 .diplomacy-table td {
@@ -1294,6 +1355,24 @@ input:focus, select:focus { border-color: var(--accent); }
  font-weight: 700;
 }
 .budget-table tfoot .budget-total .budget-value { color: #fff; }
+.budget-table tr.budget-subsection td {
+  padding-top: 8px;
+  color: var(--muted);
+  font-size: 11px;
+}
+.budget-months {
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 4px 18px 0;
+}
+.budget-months:empty { display: none; }
+.budget-month-nav {
+  min-width: 28px;
+  padding: 2px 8px;
+  font-size: 12px;
+}
+.budget-month-label { color: var(--muted); font-size: 12px; min-width: 120px; text-align: center; }

 .training-status { padding: 0 18px 16px; }
 .training-queue { padding-top: 0; }
@@ -1328,6 +1407,10 @@ input:focus, select:focus { border-color: var(--accent); }
  gap: 10px;
  text-align: left;
 }
+#city-train-list .train-name { font-weight: 600; }
+#city-train-list .train-resources { display: inline-flex; align-items: center; gap: 8px; }
+#city-train-list .train-price { color: var(--muted); font-size: 12px; font-variant-numeric: tabular-nums; }
+#city-train-list .train-time { color: var(--muted); font-size: 12px; margin-left: auto; font-variant-numeric: tabular-nums; }
 /* Local test game: the free, instant twin of an order button. */
 .free-button {
  border: 1px dashed rgba(130, 225, 170, 0.75) !important;
@@ -100,6 +100,7 @@
          <div class="layer" id="layer-highlight"></div>
          <div class="layer" id="layer-paths"></div>
          <div class="layer" id="layer-targets"></div>
+          <div class="layer" id="layer-resources"></div>
          <div class="layer" id="layer-entities"></div>
          <div class="layer city-label-layer" id="layer-labels"></div>
        </div>
@@ -118,9 +119,9 @@
          <div class="top-stats">
            <div class="stat"><span class="stat-label">Date</span><span id="stat-date" class="stat-value"></span></div>
            <div class="stat"><span class="stat-label">Population</span><span id="stat-pop" class="stat-value">0</span></div>
-            <div class="stat"><span class="stat-label">GDP</span><span id="stat-gdp" class="stat-value">€0</span></div>
-            <div class="stat"><span class="stat-label">GDP/capita</span><span id="stat-gdppc" class="stat-value">€0</span></div>
-            <div class="stat"><span class="stat-label">Budget</span><span id="stat-budget" class="stat-value">€0</span></div>
+            <div class="stat"><span class="stat-label">GDP</span><span id="stat-gdp" class="stat-value">¤0</span></div>
+            <div class="stat"><span class="stat-label">GDP/capita</span><span id="stat-gdppc" class="stat-value">¤0</span></div>
+            <div class="stat"><span class="stat-label">Budget</span><span id="stat-budget" class="stat-value">¤0</span></div>
            <div class="stat"><span class="stat-label">Popularity</span><span id="stat-approval" class="stat-value approval-neutral">—</span></div>
          </div>
        </div>
@@ -141,6 +142,7 @@
          <div id="tile-info" class="info-section hidden">
            <div id="tile-desc" class="info-title"></div>
            <div id="tile-coords" class="tile-coords"></div>
+            <div id="tile-production"></div>
            <div id="tile-ethnicity"></div>
            <div id="tile-gdp"></div>
            <div id="tile-improvements"></div>
@@ -224,6 +226,7 @@
            <button class="tab" data-tab="buildings">Buildings</button>
            <button class="tab" data-tab="people">People</button>
            <button class="tab" data-tab="budget">Budget</button>
+            <button class="tab" data-tab="economy">Economy</button>
          </div>
          <div class="tab-page active" id="city-tab-train">
            <div id="city-train-list" class="modal-body"></div>
@@ -245,6 +248,10 @@
            <div id="city-budget-sub" class="modal-sub"></div>
            <div id="city-budget-list" class="modal-body"></div>
          </div>
+          <div class="tab-page" id="city-tab-economy">
+            <div id="city-economy-sub" class="modal-sub"></div>
+            <div id="city-economy-list" class="modal-body"></div>
+          </div>
        </div>
      </div>

@@ -307,6 +314,8 @@
            <button class="tab" data-tab="cities">Cities</button>
            <button class="tab" data-tab="conflicts">Ongoing conflicts</button>
            <button class="tab" data-tab="budget">Budget</button>
+            <button class="tab" data-tab="economy">Economy</button>
+            <button class="tab" data-tab="resources">Resources</button>
          </div>
          <div class="tab-page active" id="tab-government">
            <div id="government-sub" class="modal-sub"></div>
@@ -335,8 +344,22 @@
          </div>
          <div class="tab-page" id="tab-budget">
            <div id="budget-sub" class="modal-sub"></div>
+            <div id="budget-months" class="budget-months"></div>
            <div id="budget-list" class="modal-body"></div>
          </div>
+          <div class="tab-page" id="tab-economy">
+            <div id="economy-sub" class="modal-sub"></div>
+            <div id="economy-subtabs" class="subtabs"></div>
+            <div id="economy-summary" class="modal-body"></div>
+            <div id="economy-central-bank" class="modal-body hidden"></div>
+            <div id="economy-rates" class="modal-body hidden"></div>
+          </div>
+          <div class="tab-page" id="tab-resources">
+            <div id="resources-sub" class="modal-sub"></div>
+            <div id="resources-subtabs" class="subtabs"></div>
+            <div id="resources-list" class="modal-body"></div>
+            <div id="resource-trade-list" class="modal-body hidden"></div>
+          </div>
        </div>
      </div>

@@ -7,20 +7,23 @@ export const CREDIT_SECTIONS = [
  {
    title: "Visual artists",
    note:
-      "Unit, building and nation icons drawn for game-icons.net by the artists " +
-      "below, used under CC BY 3.0.",
+      "Unit, building and resource icons drawn for game-icons.net by the " +
+      "artists below, used under CC BY 3.0.",
    entries: [
      {
        name: "Delapouite",
        detail:
          "bank, caesar, clapperboard, control tower, delivery drone, " +
-          "encirclement, graduate cap, habitat dome, jet fighter, military " +
-          "fort, modern city, old wagon, rail road, road, ship bow, shop, " +
-          "stone bust, throne",
+          "encirclement, gold mine, graduate cap, habitat dome, i-beam, jet " +
+          "fighter, melting metal, military fort, modern city, nuclear plant, " +
+          "old wagon, power plant, rail road, road, ship bow, shop, stone " +
+          "bust, throne",
      },
      {
        name: "Lorc",
-        detail: "anchor, crossed sabres, radar dish, rocket",
+        detail:
+          "anchor, crossed sabres, cut diamond, diamond hard, microchip, " +
+          "radar dish, rocket, shiny apple",
      },
      {
        name: "Lord Berandas",
@@ -29,7 +32,8 @@ export const CREDIT_SECTIONS = [
      { name: "Cathelineau", detail: "battleship" },
      { name: "Pierre Leducq", detail: "anti-aircraft gun" },
      { name: "Quoting", detail: "field gun" },
-      { name: "Skoll", detail: "FAMAS" },
+      { name: "sbed", detail: "electric" },
+      { name: "Skoll", detail: "FAMAS, solar power" },
    ],
  },
  {
@@ -0,0 +1,22 @@
+// The viewer's currency. Money is quoted in whatever nation the player runs, so
+// every money string reads in the right unit. The symbol is set from the
+// snapshot; until then a neutral mark stands in.
+
+import { groupDigits } from "../../shared/text_format.js";
+
+let symbol = "¤";
+
+export function setCurrency(currency) {
+  if (currency && currency.symbol) symbol = currency.symbol;
+}
+
+export function currencySymbol() {
+  return symbol;
+}
+
+// A signed money amount, with an optional "/h" for hourly figures.
+export function moneyText(value, { signed = true, perHour = false } = {}) {
+  const amount = `${symbol}${groupDigits(Math.round(Math.abs(value)))}`;
+  const sign = signed ? (value < 0 ? "−" : "+") : "";
+  return `${sign}${amount}${perHour ? "/h" : ""}`;
+}
@@ -17,6 +17,7 @@ import { panelMethods } from "./game_screen/panels.js";
 import { CompletionWatcher } from "./game_screen/completions.js";
 import { BombardmentSfx, AirStrikeSfx, zoomVolume } from "./game_screen/bombing.js";
 import { audio } from "./audio.js";
+import { setCurrency } from "./currency.js";

 export class GameScreen {
  constructor(network, config) {
@@ -37,15 +38,16 @@ export class GameScreen {
    this._trainingCityId = 0;
    this._cityBuildings = new Map();
    this._population = new Map();
-    this._gdpBaseline = new Map();
+    this._productionBaseline = new Map();
+    this._regionProductionBase = new Map();
    this._tileEthnicity = new Map();
    this._populationVersion = undefined;
-    this._gdpBaselineVersion = undefined;
+    this._productionBaselineVersion = undefined;
    this._ethnicityVersion = undefined;
    this._territoryVersion = undefined;
    this._regionVersion = undefined;
-    this._tileGdpPenalties = new Map();
-    this._tileBattleGdpDeficits = new Map();
+    this._tileProductionPenalties = new Map();
+    this._tileBattleProductionDeficits = new Map();
    this._territoryOwner = new Map();
    this._tileRegion = new Map();
    this._gdpExpanded = false;
@@ -92,6 +94,7 @@ export class GameScreen {
        highlight: $("#layer-highlight"),
        paths: $("#layer-paths"),
        targets: $("#layer-targets"),
+        resources: $("#layer-resources"),
        entities: $("#layer-entities"),
        labels: $("#layer-labels"),
      }
@@ -159,6 +162,7 @@ export class GameScreen {
  onState(state) {
    this.snapshot = state;
    this.localCiv = state.viewer;
+    setCurrency(state.viewerStats && state.viewerStats.currency);
    this.testing = !!(state.testing || (this.config && this.config.testing));
    this.civilisations = state.civs.map(
      (c) => CIVILISATIONS.find((full) => full.id === c.id) || { id: c.id, name: c.name, primaryColour: "#888" }
@@ -176,14 +180,17 @@ export class GameScreen {
      this._populationVersion = versionOf("population");
      this._population = new Map(state.population.map((e) => [`${e[0]},${e[1]}`, e[2]]));
    }
-    // The opening GDP per capita of every land tile never changes, so it is
-    // built once and kept across the deltas that omit it.
-    if (versionChanged("gdpBaseline", this._gdpBaselineVersion)) {
-      this._gdpBaselineVersion = versionOf("gdpBaseline");
-      this._gdpBaseline = new Map(
-        (state.gdpBaseline || []).map((e) => [`${e[0]},${e[1]}`, e[2]])
+    // The opening production per head of every land tile never changes, so it
+    // is built once and kept across the deltas that omit it.
+    if (versionChanged("productionBaseline", this._productionBaselineVersion)) {
+      this._productionBaselineVersion = versionOf("productionBaseline");
+      this._productionBaseline = new Map(
+        (state.productionBaseline || []).map((e) => [`${e[0]},${e[1]}`, e[2]])
      );
    }
+    // Each region's production per head, before tile modifiers. It moves with
+    // production and prices, so it is rebuilt from every snapshot.
+    this._regionProductionBase = new Map((state.regionProductionBase || []).map((e) => [e[0], e[1]]));
    if (versionChanged("ethnicity", this._ethnicityVersion)) {
      this._ethnicityVersion = versionOf("ethnicity");
      this._tileEthnicity = new Map(
@@ -198,11 +205,11 @@ export class GameScreen {
      this._regionVersion = versionOf("regions");
      this._tileRegion = new Map((state.regions || []).map((e) => [`${e[0]},${e[1]}`, e[2]]));
    }
-    this._tileGdpPenalties = new Map(
-      (state.tileGdpPenalties || []).map((e) => [`${e[0]},${e[1]}`, e[2]])
+    this._tileProductionPenalties = new Map(
+      (state.tileProductionPenalties || []).map((e) => [`${e[0]},${e[1]}`, e[2]])
    );
-    this._tileBattleGdpDeficits = new Map(
-      (state.tileBattleGdpDeficits || []).map((e) => [`${e[0]},${e[1]}`, e[2]])
+    this._tileBattleProductionDeficits = new Map(
+      (state.tileBattleProductionDeficits || []).map((e) => [`${e[0]},${e[1]}`, e[2]])
    );
    this._battles = new Set((state.battles || []).map((e) => `${e[0]},${e[1]}`));
    this._cityBuildings = new Map();
@@ -227,6 +234,9 @@ export class GameScreen {
    // Mirror the viewer's repeatable-research bonuses used by prediction.
    this.map.railSpeed = (state.viewerStats || {}).railSpeed || 0;
    this.map.applySnapshot(state);
+    // The delivery graph is delta-dropped while unchanged, so only replace the
+    // view's copy when the snapshot actually carried one.
+    if (state.resourceGraph) this.map.setResourceGraph(state.resourceGraph);
    // Refresh an active economic map mode against the new figures.
    this._refreshEconomicMode();
    this.selectedUnitIds = this.selectedUnitIds.filter((id) => this._unit(id));
@@ -3,7 +3,7 @@
 // on the GameScreen instance (composed in ../game_screen.js) and only read the
 // snapshot and forward orders.

-import { describeNews } from "../modals.js";
+import { describeNews, marketPricesFrom, quotedMoney, quotedBuildCost } from "../modals.js";
 import { compact, groupDigits, hours, improvements as fmtImprovements } from "../../../shared/text_format.js";
 import {
  CIVILISATIONS,
@@ -15,7 +15,7 @@ import {
  NEWS_TECHNOLOGY,
  NEWS_JOIN,
  ECONOMY,
-  EFFECT_GDP,
+  EFFECT_PRODUCTION,
  APPROVAL,
  effectValue,
  pillageSteps,
@@ -23,29 +23,22 @@ import {
  TRANSPORT_IMPROVEMENTS,
  transportImprovement,
  TILE_IMPROVEMENTS,
+  RESOURCE_BUILDINGS,
+  resourceById,
+  RESOURCES,
+  RESOURCE_RULES,
+  tileImprovementById,
  AIR_STRIKE,
 } from "../../../shared/data.js";
-import { defenseFactors, unitDefense, gdpPerCapitaFactors, gdpPerCapitaFromFactors, popularityDisplay } from "../../../shared/rules.js";
+import { defenseFactors, unitDefense, productionFactors, productionMultiplier, popularityDisplay } from "../../../shared/rules.js";
+import { formatEnergy, formatResourceAmount, foodNeedPerDay, protoUpkeep, tileImprovementResourceCost } from "../../../shared/resources.js";
 import { dateString, HOURS_PER_DAY, hoursInNextMonth } from "../../../shared/game_clock.js";
 import { DEFAULT_UNIT_SPEED } from "../../../shared/game_state/constants.js";
-import { parseKey } from "../../../shared/hex.js";
 import { ethnicityChart } from "../ui/ethnicity.js";
 import { isEconomicMode } from "../map_view/economic.js";
 import { isWaterTile } from "../map_view/textures.js";
 import { audio } from "../audio.js";
-
-// A tiny memo cache keyed by bucket and key, used while a per-tile economic
-// figure is computed for every tile at once.
-function memo(caches, bucket, key, compute) {
-  if (!caches) return compute();
-  let cache = caches[bucket];
-  if (!cache) {
-    cache = new Map();
-    caches[bucket] = cache;
-  }
-  if (!cache.has(key)) cache.set(key, compute());
-  return cache.get(key);
-}
+import { currencySymbol } from "../currency.js";

 export const panelMethods = {
  _bindHud() {
@@ -98,6 +91,8 @@ export const panelMethods = {
      this.sendOrder({ type: "policy", policy, ethnicity });
    this.nationModal.onRevokePolicy = (policy) =>
      this.sendOrder({ type: "revoke_policy", policy });
+    this.nationModal.onSetInterestRate = (rate) =>
+      this.sendOrder({ type: "set_interest_rate", rate });

    $("#unit-attack")
      .on("mouseenter", (event) => this._showStatTooltip($(event.currentTarget)))
@@ -286,12 +281,12 @@ export const panelMethods = {
    // A unit in combat cannot pillage.
    if (this._battles.has(`${coords[0]},${coords[1]}`)) return null;
    const population = this._population.get(`${coords[0]},${coords[1]}`) || 0;
-    const { steps, gdpMultiplier } = pillageSteps(population, units.length);
+    const { steps, productionMultiplier } = pillageSteps(population, units.length);
    const ordered = units.slice().sort((a, b) => a.hp / a.maxHp - b.hp / b.maxHp);
    const healed = ordered.map((unit, index) =>
      Math.min(unit.maxHp, unit.hp + steps[index].heal) - unit.hp
    );
-    return { population, steps, gdpMultiplier, healed };
+    return { population, steps, productionMultiplier, healed };
  },

  _updatePillageButton(units) {
@@ -308,8 +303,8 @@ export const panelMethods = {
      .removeClass("hidden")
      .attr(
        "data-tooltip",
-        `Removes ${groupDigits(Math.round(removed))} people (${share.toFixed(0)}%)  ·  ` +
-          `GDP/capita ×${forecast.gdpMultiplier.toFixed(2)}  ·  heals ${heals} HP`
+          `Removes ${groupDigits(Math.round(removed))} people (${share.toFixed(0)}%)  ·  ` +
+          `production ×${forecast.productionMultiplier.toFixed(2)}  ·  heals ${heals} HP`
      );
  },

@@ -408,9 +403,10 @@ export const panelMethods = {
    }
    const cost = (AIR_STRIKE.cost || 0) * units.length;
    if (cost > budget) {
+      const prices = marketPricesFrom(this.snapshot);
      return {
        title: "Insufficient budget",
-        message: `An air strike costs €${groupDigits(cost)}, which the treasury cannot cover.`,
+        message: `An air strike costs ${currencySymbol()}${groupDigits(quotedMoney(cost, prices))}, which the treasury cannot cover.`,
      };
    }
    return null;
@@ -517,9 +513,9 @@ export const panelMethods = {
    // stat can show whether it rose or fell since.
    const month = ((state.monthly || [])[this.localCiv]) || null;
    $("#stat-pop").text(compact(stats.population || 0));
-    $("#stat-gdp").text(`€${compact(stats.gdp || 0)}`);
-    $("#stat-gdppc").text(`€${compact(stats.gdpPerCapita || 0)}`);
-    $("#stat-budget").text(`€${compact(stats.budget || 0)}`);
+    $("#stat-gdp").text(`${currencySymbol()}${compact(stats.gdp || 0)}`);
+    $("#stat-gdppc").text(`${currencySymbol()}${compact(stats.gdpPerCapita || 0)}`);
+    $("#stat-budget").text(`${currencySymbol()}${compact(stats.budget || 0)}`);
    // GDP, population and GDP/capita double the arrow past a 10% month-on-month
    // move; the others only ever show one.
    this._updateStatArrow("stat-pop", stats.population, month && month.population, 0.1);
@@ -621,7 +617,7 @@ export const panelMethods = {
    }
    const expected = net * hoursInNextMonth(totalHours || 0);
    const sign = expected < 0 ? "−" : "+";
-    this._setStatTooltip("stat-budget", `${sign}€${compact(Math.abs(expected))}/mo`);
+    this._setStatTooltip("stat-budget", `${sign}${currencySymbol()}${compact(Math.abs(expected))}/mo`);
  },

  // The summary's popularity figure: white while it sits in the neutral band
@@ -920,7 +916,10 @@ export const panelMethods = {
    $("#tile-desc").text(this._tileDescription(coords, owner, tile, regionCity));
    $("#tile-coords").text(`Tile (${coords.x}, ${coords.y})`);
    this._renderTilePeople(k);
-    this._renderTileGdp(owner >= 0 ? this._tileGdpBreakdown(coords, owner, city, tile) : null);
+    this._renderTileProduction(
+      this._tileResourceProduction(coords, owner, city, tile)
+    );
+    this._renderRegionGdp(owner >= 0 ? regionCity : null);
    const transport = this.map.railways.has(k)
      ? ["Railway"]
      : this.map.roads.has(k)
@@ -934,7 +933,7 @@ export const panelMethods = {
    if (this.map.trenches.has(k)) works.push("Trench");
    const militaryWorks = this.map.tileImprovements.get(k);
    if (militaryWorks) {
-      const proto = TILE_IMPROVEMENTS.find((entry) => entry.id === militaryWorks.id);
+      const proto = tileImprovementById(militaryWorks.id);
      works.push(proto ? proto.name : militaryWorks.id);
    }
    $("#tile-improvements").text(
@@ -968,7 +967,7 @@ export const panelMethods = {
      (entry) => entry.coords[0] === coords.x && entry.coords[1] === coords.y
    );
    if (!work) return;
-    const proto = TILE_IMPROVEMENTS.find((improvement) => improvement.id === work.id);
+    const proto = tileImprovementById(work.id);
    const name = proto ? proto.name : work.id;
    const total = Math.max(work.totalHours || 0, 0.0001);
    const elapsed = work.elapsedHours || 0;
@@ -1011,7 +1010,8 @@ export const panelMethods = {

  // A square icon button for one buildable improvement: the type's icon with
  // its cost beneath, and the name (plus upkeep and build time) in the tooltip.
-  _improvementButton(improvement, { className, costLabel, title, disabled, current }) {
+  // A `costLabel` override replaces the resource cost (used by the free button).
+  _improvementButton(improvement, { className, costLabel, title, disabled, current, prices } = {}) {
    const classes = `aero improvement-btn improvement-icon-btn ${className || ""}`;
    const $button = $(`<button type='button' class='${classes}'></button>`)
      .attr("title", title)
@@ -1020,15 +1020,83 @@ export const panelMethods = {
    $button.append(
      $("<img class='improvement-icon'>")
        .attr("src", `assets/${improvement.icon}`)
-        .attr("alt", improvement.name),
-      $("<span class='improvement-cost'></span>").text(costLabel)
+        .attr("alt", improvement.name)
    );
+    if (costLabel !== undefined) {
+      $button.append($("<span class='improvement-cost'></span>").text(costLabel));
+    } else {
+      $button.append(this._improvementCost(improvement, prices));
+    }
    return $button;
  },

-  // One square icon button per transport and military improvement, plus a
-  // control to remove the one already standing on the tile. Shown only on a
-  // controlled land tile; an unaffordable improvement is greyed out.
+  // The cost line under an improvement icon: the steel, electricity and
+  // high-tech it spends, each with its resource icon, then the full price at
+  // today's market (build cost plus the material bill) in parentheses.
+  _improvementCost(improvement, prices) {
+    const costs = tileImprovementResourceCost(improvement);
+    const $cost = $("<span class='improvement-cost'></span>");
+    const items = [];
+    for (const id of ["steel", "energy", "hightech"]) {
+      if (!(costs[id] > 0)) continue;
+      const proto = resourceById(id);
+      items.push(
+        $("<span class='cost-res'></span>").append(
+          $("<img class='cost-icon'>")
+            .attr("src", `assets/${proto.icon}`)
+            .attr("alt", proto.name)
+            .attr("title", proto.name),
+          $("<span></span>").text(formatResourceAmount(id, costs[id]))
+        )
+      );
+    }
+    items.push(
+      $("<span class='cost-money'></span>").text(
+        `(${currencySymbol()}${compact(quotedBuildCost(improvement.buildCost, costs, prices))})`
+      )
+    );
+    items.forEach((item, index) => {
+      if (index > 0) $cost.append(" ");
+      $cost.append(item);
+    });
+    return $cost;
+  },
+
+  // The same cost as plain text, for a tooltip: the resource amounts then the
+  // market price.
+  _improvementCostText(improvement, prices) {
+    const costs = tileImprovementResourceCost(improvement);
+    const parts = [];
+    for (const id of ["steel", "energy", "hightech"]) {
+      if (costs[id] > 0) {
+        parts.push(`${formatResourceAmount(id, costs[id])} ${resourceById(id).name.toLowerCase()}`);
+      }
+    }
+    parts.push(`(${currencySymbol()}${compact(quotedBuildCost(improvement.buildCost, costs, prices))})`);
+    return parts.join(", ");
+  },
+
+  // The daily resource upkeep of a tile work, for its tooltip. Transport wears
+  // per tile rather than as a share of its cost.
+  _improvementUpkeepText(improvement) {
+    if (transportImprovement(improvement.id)) {
+      const steel = RESOURCE_RULES.transportUpkeepSteel[improvement.id] || 0;
+      return `${formatResourceAmount("steel", steel)} steel`;
+    }
+    const upkeep = protoUpkeep(improvement, improvement.buildCost || 0);
+    const parts = [];
+    for (const id of ["steel", "energy", "hightech"]) {
+      if (upkeep[id] > 0) {
+        parts.push(`${formatResourceAmount(id, upkeep[id])} ${resourceById(id).name.toLowerCase()}`);
+      }
+    }
+    return parts.length > 0 ? parts.join(", ") : "no upkeep";
+  },
+
+  // One square icon button per improvement, grouped under a category heading:
+  // military first, then transportation, then economic (resource producers),
+  // plus a control to remove the one already standing on the tile. Shown only
+  // on a controlled land tile; an unaffordable improvement is greyed out.
  _renderImprovementActions(coords, buildable, current) {
    const $row = $("#tile-improvement-actions");
    if (!$row.length) return;
@@ -1036,23 +1104,58 @@ export const panelMethods = {
    if (!buildable) return;
    const budget = (this.snapshot.viewerStats || {}).budget || 0;
    const testing = !!this.testing;
+    const gdp = (this.snapshot.viewerStats || {}).gdp || 0;
+    const speed = (this.snapshot.viewerStats || {}).constructionSpeed || 0;
+    const prices = marketPricesFrom(this.snapshot);
+    const standing = this.map.tileImprovements.get(`${coords.x},${coords.y}`) || null;
+    const standingProto = standing ? tileImprovementById(standing.id) : null;
+    const isResource = !!(standingProto && standingProto.resource);
+
+    // Military tile works. They cost resources and take production time, so the
+    // tooltip names the expected hours alongside the upkeep.
+    const military = [];
+    for (const improvement of TILE_IMPROVEMENTS) {
+      if (improvement.coastal && !this._tileIsCoastal(coords)) continue;
+      const built = !!(standing && standing.id === improvement.id);
+      const affordable = budget >= improvement.buildCost;
+      const buildHours = ECONOMY.trainingHours(gdp, improvement.buildCost) / (1 + speed);
+      const title = standing && !built
+        ? `${improvement.name} — another improvement already stands here`
+        : affordable
+          ? `${improvement.name} — ${this._improvementCostText(improvement, prices)} · ` +
+            `${this._improvementUpkeepText(improvement)}/day · ${hours(buildHours)} to build`
+          : `${improvement.name} — needs ${this._improvementCostText(improvement, prices)}`;
+      const $button = this._improvementButton(improvement, {
+        className: "tile-btn",
+        title,
+        disabled: !!standing || !affordable,
+        current: built,
+        prices,
+      });
+      $button.on("click", () => this._buildTileImprovement(coords, improvement.id));
+      military.push($button);
+    }
+
+    // Transportation: roads and railways, bought outright and laid at once.
+    const transport = [];
    for (const improvement of TRANSPORT_IMPROVEMENTS) {
      const isCurrent = current === improvement.id;
      const affordable = budget >= improvement.buildCost;
      const title = isCurrent
        ? `${improvement.name} — already built on this tile`
        : affordable
-          ? `${improvement.name} — €${groupDigits(improvement.maintenance)}/tile·h upkeep`
-          : `${improvement.name} — not enough budget (€${groupDigits(improvement.buildCost)} needed)`;
+          ? `${improvement.name} — ${this._improvementCostText(improvement, prices)} · ` +
+            `${this._improvementUpkeepText(improvement)}/day upkeep`
+          : `${improvement.name} — needs ${this._improvementCostText(improvement, prices)}`;
      const $button = this._improvementButton(improvement, {
        className: "transport-btn",
-        costLabel: `€${compact(improvement.buildCost)}`,
        title,
        disabled: isCurrent || !affordable,
        current: isCurrent,
+        prices,
      });
      $button.on("click", () => this._buildImprovement(coords, improvement.id, false));
-      $row.append($button);
+      transport.push($button);
      // A local test game may raise it for free and at once.
      if (testing && !isCurrent) {
        const $free = this._improvementButton(improvement, {
@@ -1063,48 +1166,78 @@ export const panelMethods = {
          current: false,
        });
        $free.on("click", () => this._buildImprovement(coords, improvement.id, true));
-        $row.append($free);
+        transport.push($free);
      }
    }
    if (current) {
-      const name = transportImprovement(current) ? transportImprovement(current).name : current;
-      const $remove = $("<button type='button' class='aero improvement-btn remove'></button>")
-        .text(`Remove ${name}`)
-        .on("click", () => this._removeImprovement(coords));
-      $row.append($remove);
+      const proto = transportImprovement(current);
+      const name = proto ? proto.name : current;
+      transport.push(
+        $("<button type='button' class='aero improvement-btn remove'></button>")
+          .text(`Remove ${name}`)
+          .on("click", () => this._removeImprovement(coords))
+      );
    }

-    // Military tile improvements. They cost money and take production time, so
-    // the tooltip names the expected hours alongside the upkeep.
-    const military = this.map.tileImprovements.get(`${coords.x},${coords.y}`) || null;
-    const gdp = (this.snapshot.viewerStats || {}).gdp || 0;
-    const speed = (this.snapshot.viewerStats || {}).constructionSpeed || 0;
-    for (const improvement of TILE_IMPROVEMENTS) {
-      if (improvement.coastal && !this._tileIsCoastal(coords)) continue;
-      const built = !!(military && military.id === improvement.id);
-      const affordable = budget >= improvement.buildCost;
-      const buildHours = ECONOMY.trainingHours(gdp, improvement.buildCost) / (1 + speed);
-      const title = military && !built
-        ? `${improvement.name} — another improvement already stands here`
-        : affordable
-          ? `${improvement.name} — €${groupDigits(improvement.maintenance)}/h upkeep · ${hours(buildHours)} to build`
-          : `${improvement.name} — not enough budget (€${groupDigits(improvement.buildCost)} needed)`;
-      const $button = this._improvementButton(improvement, {
-        className: "tile-btn",
-        costLabel: `€${compact(improvement.buildCost)}`,
-        title,
-        disabled: !!military || !affordable,
-        current: built,
-      });
-      $button.on("click", () => this._buildTileImprovement(coords, improvement.id));
-      $row.append($button);
+    // Economic: resource producers. They live on their own land, take
+    // production time and feed the delivery graph; only one may stand on a
+    // tile.
+    const economic = [];
+    if (!isResource) {
+      for (const producer of RESOURCE_BUILDINGS) {
+        if (producer.coastal && !this._tileIsCoastal(coords)) continue;
+        const built = !!(standing && standing.id === producer.id);
+        const affordable = budget >= producer.buildCost;
+        const buildHours = ECONOMY.trainingHours(gdp, producer.buildCost) / (1 + speed);
+        // Some producers are locked behind a technology (the fusion plant).
+        const techIndex = producer.requiresTechnology
+          ? TECHNOLOGIES.findIndex((tech) => tech.id === producer.requiresTechnology)
+          : -1;
+        const locked = techIndex >= 0 && !this._researched.has(techIndex);
+        const out = producer.resource === "energy"
+          ? formatEnergy(producer.outputPerDay)
+          : `${compact(producer.outputPerDay)} ${producer.resource}/day`;
+        const title = locked
+          ? `${producer.name} — requires ${TECHNOLOGIES[techIndex].name}`
+          : standing && !built
+            ? `${producer.name} — another building already stands here`
+            : affordable
+              ? `${producer.name} — ${out} · ${this._improvementCostText(producer, prices)} · ` +
+                `${hours(buildHours)} to build`
+              : `${producer.name} — needs ${this._improvementCostText(producer, prices)}`;
+        const $button = this._improvementButton(producer, {
+          className: "tile-btn resource-btn",
+          title,
+          disabled: !!standing || !affordable || locked,
+          current: built,
+          prices,
+        });
+        $button.on("click", () => this._buildTileImprovement(coords, producer.id));
+        economic.push($button);
+      }
    }
-    if (military) {
-      const name = (TILE_IMPROVEMENTS.find((i) => i.id === military.id) || {}).name || military.id;
+    if (standing) {
+      const name = standingProto ? standingProto.name : standing.id;
      const $remove = $("<button type='button' class='aero improvement-btn remove'></button>")
        .text(`Remove ${name}`)
        .on("click", () => this._removeTileImprovement(coords));
-      $row.append($remove);
+      // A standing work is removed from its own category.
+      if (isResource) economic.push($remove);
+      else military.push($remove);
+    }
+
+    for (const group of [
+      { label: "Military", buttons: military },
+      { label: "Transportation", buttons: transport },
+      { label: "Economic", buttons: economic },
+    ]) {
+      if (group.buttons.length === 0) continue;
+      const $group = $("<div class='improvement-group'></div>");
+      $group.append($("<div class='improvement-category'></div>").text(group.label));
+      const $buttons = $("<div class='improvement-row'></div>");
+      for (const $button of group.buttons) $buttons.append($button);
+      $group.append($buttons);
+      $row.append($group);
    }
  },

@@ -1216,66 +1349,66 @@ export const panelMethods = {
    $container.append(ethnicityChart(makeup, this.civilisations, 104));
  },

-  // The base GDP per capita of a claimable tile plus every factor that shapes
-  // it, mirroring the server's getTileGdpPerCapita through the shared helper.
-  // The region that develops the tile supplies the building bonus; government
-  // and research supply the nation-wide one.
-  _tileGdpBreakdown(coords, owner, city, tile, caches = null) {
+  // The resources a tile produces in a day, each amount already carrying the
+  // tile's production modifiers, plus the factor list behind it. Food comes from
+  // the people on the tile; every other resource from the work standing there.
+  _tileResourceProduction(coords, owner, city, tile) {
    const k = `${coords.x},${coords.y}`;
    const regionCity =
      city || (this.snapshot.cities || []).find((c) => c.id === this._tileRegion.get(k));
-    const regionalModifier = regionCity
-      ? memo(caches, "regional", regionCity.id, () => this._cityGdpModifier(regionCity))
-      : 0;
-    const nationalModifier = memo(caches, "national", owner, () => this._nationalGdpModifier(owner));
-    const factors = gdpPerCapitaFactors(tile, {
-      cityKind: city ? (city.isCapital ? "capital" : "city") : null,
-      nextToCity: !city && memo(caches, "nextToCity", k, () => this._isNextToCity(coords, owner)),
-      pillagePenalty: this._tileGdpPenalties.has(k) ? this._tileGdpPenalties.get(k) : 1,
-      battleDeficit: this._tileBattleGdpDeficits.get(k) || 0,
-      regionalMultiplier: 1 + regionalModifier,
-      regionalLabel: regionCity ? regionCity.name : null,
-      nationalMultiplier: 1 + nationalModifier,
-      portGdp: regionCity
-        ? memo(caches, "portGdp", regionCity.id, () => this._regionPortGdp(regionCity))
-        : 0,
-      naturalGrowth: memo(caches, "growth", k, () => this._naturalTileGdpGrowth(k)),
-    });
-    return {
-      base: ECONOMY.baseGdpPerCapita,
-      factors,
-      total: gdpPerCapitaFromFactors(ECONOMY.baseGdpPerCapita, factors),
-    };
+    const factors = this._productionFactors(coords, owner, city, tile, regionCity);
+    const multiplier = productionMultiplier(factors);
+    const amounts = { energy: 0, steel: 0, food: 0, luxury: 0, hightech: 0 };
+    const population = this._population.get(k) || 0;
+    let foodMultiplier = 1;
+    if (population > 0 && tile) {
+      foodMultiplier = regionCity ? this._regionFoodMultiplier(regionCity) : 1;
+      const factor = RESOURCE_RULES.tileFoodFactor[tile.terrainType] ?? 1;
+      amounts.food = foodNeedPerDay(population) * factor * foodMultiplier * multiplier;
+    }
+    const improvement = this.map.tileImprovements.get(k);
+    const proto = improvement ? tileImprovementById(improvement.id) : null;
+    if (proto && proto.resource && proto.outputPerDay) {
+      amounts[proto.resource] += proto.outputPerDay * multiplier;
+    }
+    return { amounts, factors, foodMultiplier };
  },

-  // The flat GDP per capita a region's ports add to every tile it covers,
-  // mirroring the server: 1000 per port level for each sea tile beside the city.
-  _regionPortGdp(city) {
+  // The production modifiers of one tile: terrain, settlement, war and the
+  // region's and nation's own bonuses. Mirrors the server's `productionFactors`
+  // inputs so the tile panel and the simulation explain the same figure.
+  _productionFactors(coords, owner, city, tile, regionCity) {
+    const k = `${coords.x},${coords.y}`;
+    return productionFactors(tile, {
+      cityKind: city ? (city.isCapital ? "capital" : "city") : null,
+      nextToCity: !city && this._isNextToCity(coords, owner),
+      pillagePenalty: this._tileProductionPenalties.has(k) ? this._tileProductionPenalties.get(k) : 1,
+      battleDeficit: this._tileBattleProductionDeficits.get(k) || 0,
+      trench: this.map.trenches.has(k),
+      regionalMultiplier: 1 + (regionCity ? this._cityProductionModifier(regionCity) : 0),
+      regionalLabel: regionCity ? regionCity.name : null,
+      nationalMultiplier: 1 + this._nationalProductionModifier(owner),
+    });
+  },
+
+  // The extra food a region's ports bring in, mirroring the server: 5% per
+  // adjacent sea tile per port level.
+  _regionFoodMultiplier(city) {
    const protos = this.snapshot.buildings || [];
    let bonus = 0;
    for (const [index, level] of Object.entries(city.buildings || {})) {
      const proto = protos[index];
-      if (proto && proto.mechanic === "port_gdp") {
-        bonus += (proto.gdpPerCapitaPerSeaTilePerLevel || 0) * level;
+      if (proto && proto.mechanic === "port_production") {
+        bonus += (proto.foodPerSeaTilePerLevel || 0) * level;
      }
    }
-    if (bonus === 0) return 0;
+    if (bonus === 0) return 1;
    let sea = 0;
    for (const neighbour of this.map.topology.neighbours(city.coords[0], city.coords[1])) {
      const tile = this.map.getTile(neighbour);
      if (tile && tile.terrainClass === "Sea") sea += 1;
    }
-    return bonus * sea;
-  },
-
-  // The flat GDP per capita a tile has gained since January 2000, mirroring the
-  // server: its opening figure times the daily rate, once per day elapsed.
-  _naturalTileGdpGrowth(k) {
-    const baseline = this._gdpBaseline.get(k) || 0;
-    if (!baseline) return 0;
-    const totalHours = (this.snapshot && this.snapshot.totalHours) || 0;
-    const days = Math.floor(Math.max(0, totalHours) / HOURS_PER_DAY);
-    return baseline * ECONOMY.naturalGdpGrowthPerDay * days;
+    return 1 + bonus * sea;
  },

  // -------------------------------------------------------- map modes -----
@@ -1301,16 +1434,21 @@ export const panelMethods = {
  },

  // One figure per land tile for an economic mode, with the range the legend
-  // and the colour scale need. GDP per capita mirrors the tile panel's formula;
-  // population is the snapshot's raw per-tile count.
+  // and the colour scale need. GDP per capita is the region's, so every tile of
+  // a region shares one colour; population is the raw per-tile count.
  _computeEconomicValues(mode) {
    const values = new Map();
    let min = Infinity;
    let max = -Infinity;
    if (!this.map || !this.map.tiles) return { values, min: 0, max: 0 };
-    const cities = this.snapshot.cities || [];
-    const cityByKey = new Map(cities.map((c) => [`${c.coords[0]},${c.coords[1]}`, c]));
-    const caches = mode === "gdp" ? {} : null;
+    const gdpPerCapita = new Map();
+    if (mode === "gdp") {
+      for (const city of this.snapshot.cities || []) {
+        const stats = this._cityStats(city.id);
+        const population = stats.population || 0;
+        gdpPerCapita.set(city.id, population > 0 ? (stats.gdp || 0) / population : 0);
+      }
+    }
    for (const k in this.map.tiles) {
      const tile = this.map.tiles[k];
      if (isWaterTile(tile)) continue;
@@ -1318,10 +1456,7 @@ export const panelMethods = {
      if (mode === "population") {
        value = this._population.get(k) || 0;
      } else {
-        const coords = parseKey(k);
-        const owner = this._territoryOwner.has(k) ? this._territoryOwner.get(k) : -1;
-        const city = cityByKey.get(k) || null;
-        value = this._tileGdpBreakdown(coords, owner, city, tile, caches).total;
+        value = gdpPerCapita.get(this._tileRegion.get(k)) || 0;
      }
      values.set(k, value);
      if (value < min) min = value;
@@ -1331,34 +1466,35 @@ export const panelMethods = {
    return { values, min, max };
  },

-  // The GDP bonus a single city's own buildings give.
-  _cityGdpModifier(city) {
+  // The production bonus a single city's own buildings give.
+  _cityProductionModifier(city) {
    let total = 0;
    for (const indexStr of Object.keys(city.buildings || {})) {
      const proto = BUILDINGS[Number(indexStr)];
      if (!proto) continue;
      const level = city.buildings[indexStr];
      for (const e of proto.effects) {
-        if (e.stat === EFFECT_GDP) total += effectValue(e, level);
+        if (e.stat === EFFECT_PRODUCTION) total += effectValue(e, level);
      }
    }
    return total;
  },

-  // The GDP bonus a nation gets from its government and researched technology.
-  _nationalGdpModifier(civ) {
+  // The production bonus a nation gets from its government and researched
+  // technology.
+  _nationalProductionModifier(civ) {
    let total = 0;
    const government = GOVERNMENTS[(this.snapshot.government || [])[civ]];
    if (government) {
      for (const e of government.effects) {
-        if (e.stat === EFFECT_GDP) total += effectValue(e, 1);
+        if (e.stat === EFFECT_PRODUCTION) total += effectValue(e, 1);
      }
    }
    for (const index of (this.snapshot.researched || [])[civ] || []) {
      const tech = TECHNOLOGIES[index];
      if (!tech) continue;
      for (const e of tech.effects) {
-        if (e.stat === EFFECT_GDP) total += effectValue(e, 1);
+        if (e.stat === EFFECT_PRODUCTION) total += effectValue(e, 1);
      }
    }
    return total;
@@ -1377,53 +1513,64 @@ export const panelMethods = {
    return false;
  },

-  // Lists the tile's GDP per capita and each factor behind it, so a click
-  // explains exactly why the figure is what it is.
-  _renderTileGdp(breakdown) {
-    const $container = $("#tile-gdp").empty();
-    if (!breakdown) {
-      $container.text("GDP/capita: —");
+  // The tile panel's headline: what the tile actually produces, one row per
+  // resource (nothing is shown for a resource the tile does not make), with the
+  // modifiers that shape it in a hover tooltip.
+  _renderTileProduction(production) {
+    const $container = $("#tile-production").empty();
+    const rows = [];
+    for (const resource of RESOURCES) {
+      const amount = production.amounts[resource.id] || 0;
+      if (!(amount > 0)) continue;
+      const notes = [];
+      for (const factor of production.factors) {
+        if (factor.multiplier !== undefined) {
+          if (factor.multiplier === 1) continue;
+          notes.push(`${factor.label}: ×${factor.multiplier.toFixed(2)}`);
+        } else if (factor.amount) {
+          const sign = factor.amount < 0 ? "−" : "+";
+          notes.push(`${factor.label}: ${sign}${currencySymbol()}${groupDigits(Math.round(Math.abs(factor.amount)))}`);
+        }
+      }
+      if (resource.id === "food" && production.foodMultiplier !== 1) {
+        notes.push(`Port food: ×${production.foodMultiplier.toFixed(2)}`);
+      }
+      const $row = $("<div class='tile-prod-row'></div>");
+      $row.append(
+        $("<img class='resource-icon' width='16' height='16'>")
+          .attr("src", `assets/${resource.icon}`)
+          .attr("alt", resource.name),
+        $("<span class='tile-prod-name'></span>").text(resource.name),
+        $("<span class='tile-prod-value'></span>").text(
+          `${formatResourceAmount(resource.id, amount)}/day`
+        )
+      );
+      if (notes.length > 0) $row.attr("title", notes.join("\n"));
+      rows.push($row);
+    }
+    if (rows.length === 0) {
+      $container.append($("<div class='tile-prod-empty'></div>").text("No production"));
      return;
    }
-    const $mods = $("<div class='tile-gdp-mods'></div>");
-    if (!this._gdpExpanded) $mods.addClass("hidden");
-    $mods.append(
-      $("<div class='tile-gdp-mod'></div>").text(`Base €${groupDigits(breakdown.base)}`)
-    );
-    let modifierCount = 0;
-    for (const factor of breakdown.factors) {
-      // A modifier that changes nothing (×1 or ±€0) is left out.
-      if (factor.amount !== undefined) {
-        if (factor.amount === 0) continue;
-      } else if (factor.multiplier === 1) {
-        continue;
-      }
-      const value =
-        factor.amount !== undefined
-          ? `${factor.amount < 0 ? "−" : "+"}€${groupDigits(Math.round(Math.abs(factor.amount)))}`
-          : `×${factor.multiplier.toFixed(2)}`;
-      $mods.append(
-        $("<div class='tile-gdp-mod'></div>").text(`${factor.label} ${value}`)
-      );
-      modifierCount += 1;
+    for (const $row of rows) $container.append($row);
+  },
+
+  // The only place GDP per capita is shown: the region the tile belongs to. A
+  // tile never gets a per-tile figure of its own.
+  _renderRegionGdp(regionCity) {
+    const $container = $("#tile-gdp").empty();
+    if (!regionCity) {
+      $container.text("Region GDP/capita: —");
+      return;
    }
-    const $head = $("<div class='tile-gdp-head'></div>").text(
-      `GDP/capita: €${groupDigits(Math.round(breakdown.total))}`
+    const stats = this._cityStats(regionCity.id);
+    const population = stats.population || 0;
+    const perCapita = population > 0 ? (stats.gdp || 0) / population : 0;
+    $container.append(
+      $("<div class='tile-gdp-head'></div>").text(
+        `Region GDP/capita: ${currencySymbol()}${groupDigits(Math.round(perCapita))}`
+      )
    );
-    if (modifierCount > 0) {
-      $head.addClass("tile-gdp-toggle");
-      $head.append(
-        $("<span class='tile-gdp-caret'></span>").text(this._gdpExpanded ? "▾" : "▸")
-      );
-      $head.on("click", () => {
-        this._gdpExpanded = !this._gdpExpanded;
-        $mods.toggleClass("hidden", !this._gdpExpanded);
-        $head.find(".tile-gdp-caret").text(this._gdpExpanded ? "▾" : "▸");
-      });
-      $container.append($head, $mods);
-    } else {
-      $container.append($head);
-    }
  },

  // The tile/city panel and the unit panel are independent docks, so either
@@ -1484,12 +1631,19 @@ export const panelMethods = {
      queue: this._trainingQueue(city.id),
      civs: this.civilisations,
      ethnicMakeup: cityStats.ethnicMakeup || [],
+      // The region's private-sector cash basket and the currencies it names.
+      cash: cityStats.cash || {},
+      cashValue: cityStats.cashValue || 0,
+      debt: cityStats.debt || 0,
+      currencies: stats.currencies || [],
      approval: cityStats.approval,
      // The region's tax base and approval price an upgrade's expected income.
      base: cityStats.base || 0,
      // Construction technology shortens the displayed build times.
      constructionSpeed: stats.constructionSpeed || 0,
      taxMultiplier: this._taxMultiplier(cityStats.approval),
+      // Today's market prices, so build costs are quoted at current rates.
+      prices: marketPricesFrom(this.snapshot),
    };
  },

@@ -1509,6 +1663,7 @@ export const panelMethods = {
    this._updateCityProgress(queue);
    const cityStats = this._cityStats(this.selectedCityId);
    this.cityModal.constructionSpeed = stats.constructionSpeed || 0;
+    this.cityModal.prices = marketPricesFrom(this.snapshot);
    const city = this._city(this.selectedCityId);
    if (city) {
      this.cityModal.refreshTrainList(this._trainableUnits(city));
@@ -1527,6 +1682,12 @@ export const panelMethods = {
      { base: cityStats.base || 0, approval: cityStats.approval }
    );
    this.cityModal.renderBudget(this._cityBudget(this.selectedCityId));
+    this.cityModal.renderEconomy(
+      cityStats.cash || {},
+      cityStats.cashValue || 0,
+      stats.currencies || [],
+      cityStats.debt || 0
+    );
  },

  _updateCityProgress(queue) {
@@ -1595,10 +1756,40 @@ export const panelMethods = {
      this._diplomacyInfo(),
      this._conflicts,
      this._politicsInfo(),
-      this._techInfo()
+      this._techInfo(),
+      this._resourcesInfo(),
+      this._moneyInfo()
    );
  },

+  // The money the Economy tab needs: the viewer's currency, everyone else's,
+  // the exchange rates, the central bank and the aggregate private-sector cash.
+  _moneyInfo() {
+    const stats = (this.snapshot && this.snapshot.viewerStats) || {};
+    return {
+      viewerCiv: this.localCiv,
+      currency: stats.currency || null,
+      currencies: stats.currencies || [],
+      exchangeRates: stats.exchangeRates || [],
+      centralBank: stats.centralBank || { rate: 0, reserves: [] },
+      privateCash: stats.privateCash || 0,
+      cities: (this.snapshot && this.snapshot.cityStats) || [],
+    };
+  },
+
+  // Everything the Resources tab needs: the nation's own stores, needs and
+  // trade from the viewer stats, plus the world market's prices, the world's
+  // supply and demand, and every nation's import/export ledger.
+  _resourcesInfo() {
+    const stats = (this.snapshot && this.snapshot.viewerStats) || {};
+    return {
+      summary: stats.resources || null,
+      market: (this.snapshot && this.snapshot.resourceMarket) || [],
+      trade: (this.snapshot && this.snapshot.resourceTrade) || [],
+      civs: this.civilisations,
+    };
+  },
+
  // The focused-research figures the technology tab reads from the snapshot.
  _techInfo() {
    const snapshot = this.snapshot || {};
@@ -1628,7 +1819,9 @@ export const panelMethods = {
      this._diplomacyInfo(),
      this._conflicts,
      this._politicsInfo(),
-      this._techInfo()
+      this._techInfo(),
+      this._resourcesInfo(),
+      this._moneyInfo()
    );
  },

@@ -1703,11 +1896,12 @@ export const panelMethods = {
  },

  _finances(stats) {
-    if (!stats || !stats.breakdown) return null;
-    // The region figures are global, so the Cities tab can show every nation's;
-    // the panel filters them to the viewer.
+    if (!stats) return null;
+    // The month reports page back through the stored budget digests; the region
+    // figures are global, so the Cities tab can show every nation's, and the
+    // panel filters them to the viewer.
    return {
-      ...stats.breakdown,
+      months: stats.budgetMonths || [],
      cities: (this.snapshot && this.snapshot.cityStats) || [],
    };
  },
@@ -47,6 +47,17 @@ export class MapView {
    this.$targets = layers.targets && layers.targets.length
      ? layers.targets
      : $("#layer-targets");
+    // Resource storage nodes and delivery legs, drawn in the economic map
+    // modes so the delivery graph is never visible on the political map.
+    this.$resources = layers.resources && layers.resources.length
+      ? layers.resources
+      : $("#layer-resources");
+    if (!this.$resources.length) {
+      this.$resources = $('<div id="layer-resources" class="layer"></div>');
+      if (this.$targets && this.$targets.length) this.$targets.after(this.$resources);
+      else this.$world.append(this.$resources);
+    }
+    this.resourceGraph = { nodes: [], links: [] };
    this.$entities = layers.entities;
    // City names live on their own layer above the entities so they are never
    // hidden behind a unit or city marker.
@@ -78,7 +89,7 @@ export class MapView {
    this.$viewport[0].style.setProperty("--camera-tilt", String(CAMERA_TILT));
    for (const $layer of [
      this.$terrain, this.$roads, this.$borders, this.$fog,
-      this.$highlight, this.$paths, this.$targets,
+      this.$highlight, this.$paths, this.$targets, this.$resources,
    ]) {
      if ($layer && $layer.length) $layer.addClass("tilted");
    }
@@ -10,6 +10,7 @@

 import { parseColour } from "./utils.js";
 import { groupDigits } from "../../../shared/text_format.js";
+import { currencySymbol } from "../currency.js";

 export const ECONOMIC_GRADIENT = [
  "#ffea46",
@@ -31,7 +32,7 @@ export const ECONOMIC_MODES = {
  gdp: {
    id: "gdp",
    label: "GDP per capita",
-    format: (value) => `€${groupDigits(Math.round(value))}`,
+    format: (value) => `${currencySymbol()}${groupDigits(Math.round(value))}`,
  },
  population: {
    id: "population",
@@ -4,11 +4,13 @@
 // and drives the economic fill and its legend. The political names themselves
 // live in ./political.js; this file only decides what is on screen.

-import { HEX_W } from "../../../shared/hex.js";
+import { HEX_W, mapToLocal } from "../../../shared/hex.js";
 import { POLITICAL_ZOOM } from "./constants.js";
 import { ECONOMIC_GRADIENT, ECONOMIC_MODES, economicColour, isEconomicMode } from "./economic.js";
 import { NEUTRAL_LAND, POLITICAL_WATER } from "./political.js";
 import { isWaterTile } from "./textures.js";
+import { makeSegment } from "./utils.js";
+import { RESOURCES } from "../../../shared/data/resources.js";

 export const MAP_MODES = ["terrain", "political", "gdp", "population"];

@@ -45,6 +47,47 @@ export const modeMethods = {
    return `${this.economicKind}:${this.economicValues.size}:${Math.round(sum)}`;
  },

+  // ------------------------------------------------- delivery graph ------
+
+  // Replaces the delivery graph shipped in the snapshot. It is only drawn in
+  // the economic modes, so a political or terrain map never reveals it.
+  setResourceGraph(graph) {
+    if (!graph) return;
+    this.resourceGraph = {
+      nodes: Array.isArray(graph.nodes) ? graph.nodes : [],
+      links: Array.isArray(graph.links) ? graph.links : [],
+    };
+    this._renderResourceGraph();
+  },
+
+  // Draws one line per delivery leg and a dot on every storage node. The layer
+  // shares the world's coordinate system, so pan and zoom move it for free.
+  _renderResourceGraph() {
+    if (!this.$resources || !this.$resources.length) return;
+    const graph = this.resourceGraph || { nodes: [], links: [] };
+    if (!this.economic || graph.links.length === 0) {
+      if (this.$resources[0].firstChild) this.$resources.empty();
+      return;
+    }
+    const colours = Object.fromEntries(RESOURCES.map((r) => [r.id, r.colour]));
+    const fragment = document.createDocumentFragment();
+    for (const link of graph.links) {
+      const [fromX, fromY, toX, toY, resource] = link;
+      const a = mapToLocal(fromX, fromY);
+      const b = mapToLocal(toX, toY);
+      fragment.appendChild(makeSegment(a, b, colours[resource] || "#ffffff", 3));
+    }
+    for (const node of graph.nodes) {
+      const point = mapToLocal(node[0], node[1]);
+      const dot = document.createElement("div");
+      dot.className = "resource-node";
+      dot.style.left = `${point.x}px`;
+      dot.style.top = `${point.y}px`;
+      fragment.appendChild(dot);
+    }
+    this.$resources.empty()[0].appendChild(fragment);
+  },
+
  // Political shows when the user asked for it, or while terrain mode is
  // zoomed far enough out. Economic modes are exclusive with it.
  _effectivePolitical() {
@@ -109,6 +152,7 @@ export const modeMethods = {
    }
    if (this.political) this._renderPoliticalLabels();
    else if (this.$politicalLabels) this.$politicalLabels.empty();
+    this._renderResourceGraph();
    this._updateLegend();
  },

@@ -12,4 +12,4 @@ export { ConfirmModal } from "./modals/confirm.js";
 export { NewsModal } from "./modals/news.js";
 export { MapModesModal } from "./modals/map_modes.js";
 export { CapabilityModal } from "./modals/capabilities.js";
-export { describeNews } from "./modals/format.js";
+export { describeNews, marketPricesFrom, quotedMoney, quotedBuildCost } from "./modals/format.js";
@@ -4,7 +4,10 @@
 // per-city cost. `breakdown` mirrors the shape both the national and the
 // regional economy use, so one renderer serves them both.

-import { percent, signedMoney, SOURCE_LABELS } from "./format.js";
+import { percent, signedMoney, money, SOURCE_LABELS } from "./format.js";
+import { BUDGET_EXPENSE_CATEGORIES, resourceById } from "../../../shared/data.js";
+import { groupDigits } from "../../../shared/text_format.js";
+import { currencySymbol } from "../currency.js";

 // Draws the table into `$list`. `expanded` is the set of open building types,
 // mutated in place; `onToggle` is called after a caret flips so the caller can
@@ -21,6 +24,7 @@ export function renderBudget($list, breakdown = {}, { expanded = new Set(), onTo
  const campaignSources = campaigns.sources || [];
  const transport = breakdown.transportUpkeep || { total: 0, sources: [] };
  const transportSources = transport.sources || [];
+  const resourceMoney = breakdown.resourceMoney || [];
  const net = breakdown.net || 0;

  $list.empty();
@@ -95,12 +99,132 @@ export function renderBudget($list, breakdown = {}, { expanded = new Set(), onTo
    }
  }

+  // What the nation spent buying each resource, and earned selling it to other
+  // countries, over the last day, shown as an hourly average.
+  if (resourceMoney.length > 0) {
+    $body.append(sectionRow("Resource trade"));
+    for (const entry of resourceMoney) {
+      const proto = resourceById(entry.id);
+      const name = proto ? proto.name : entry.id;
+      if (entry.bought > 0) {
+        $body.append(detailRow(`Bought ${name}`, -entry.bought / 24, "expense-detail"));
+      }
+      if (entry.sold > 0) {
+        $body.append(detailRow(`Sold ${name}`, entry.sold / 24, "income-detail"));
+      }
+    }
+  }
+
  const $table = $("<table class='budget-table'></table>");
  $table.append($body);
  $table.append($("<tfoot></tfoot>").append(totalRow("TOTAL", net)));
  $list.append($table);
 }

+// Renders a whole month's actual budget: the tax and resource sales earned, the
+// money each expense category spent, and the resource-trade memo. `report` is
+// the compact shape the snapshot ships (category ids, not labels). The cash
+// spent is the headline; when a category consumed materials worth more than the
+// cash it paid (the stores covered the rest), the row notes the full market
+// value. The treasury itself lives on the panel's subtitle, not in the table.
+export function renderMonthlyBudget($list, report, { expanded = new Set(), onToggle = null } = {}) {
+  if (!$list || !$list.length) return;
+  $list.empty();
+  if (!report) return;
+  const $body = $("<tbody></tbody>");
+
+  $body.append(sectionRow("Income"));
+  $body.append(monthRow("Tax income", report.income, "income", null));
+  if (report.sales > 0) {
+    $body.append(monthRow("Resource sales", report.sales, "income-detail", null));
+  }
+
+  $body.append(sectionRow("Expenses"));
+  const byId = new Map((report.expenses || []).map((entry) => [entry[0], entry]));
+  const sections = [];
+  for (const category of BUDGET_EXPENSE_CATEGORIES) {
+    const entry = byId.get(category.id);
+    if (!entry) continue;
+    const last = sections[sections.length - 1];
+    if (!last || last.group !== category.group) {
+      sections.push({ group: category.group, rows: [] });
+    }
+    sections[sections.length - 1].rows.push({
+      id: category.id,
+      label: category.label,
+      cash: entry[1],
+      economic: entry[2],
+      buys: entry[3] || [],
+    });
+  }
+  for (const section of sections) {
+    $body.append(subsectionRow(section.group));
+    for (const row of section.rows) {
+      const note = row.economic > row.cash + 1
+        ? `materials valued at ${currencySymbol()}${groupDigits(Math.round(row.economic))}`
+        : null;
+      const isOpen = expanded.has(row.id);
+      const expandable = row.buys.length > 0;
+      const $tr = monthRow(row.label, -row.cash, "expense-detail", note);
+      if (expandable) {
+        const $name = $tr.find(".budget-name");
+        $name.addClass("clickable");
+        $name.prepend($("<span class='budget-caret'></span>").text(isOpen ? "▾" : "▸"));
+        $name.on("click", () => {
+          if (expanded.has(row.id)) expanded.delete(row.id);
+          else expanded.add(row.id);
+          if (onToggle) onToggle(row.id);
+        });
+      }
+      $body.append($tr);
+      if (isOpen) {
+        for (const [resource, amount] of row.buys) {
+          const proto = resourceById(resource);
+          const name = proto ? proto.name : resource;
+          $body.append(monthRow(`   ${name}`, -amount, "expense-detail", null));
+        }
+      }
+    }
+  }
+
+  const trade = report.resourceTrade || [];
+  if (trade.length > 0) {
+    $body.append(sectionRow("Resource trade"));
+    for (const [id, bought, sold] of trade) {
+      const proto = resourceById(id);
+      const name = proto ? proto.name : id;
+      if (bought > 0) $body.append(monthRow(`Bought ${name}`, -bought, "expense-detail", null));
+      if (sold > 0) $body.append(monthRow(`Sold ${name}`, sold, "income-detail", null));
+    }
+  }
+
+  const $table = $("<table class='budget-table'></table>");
+  $table.append($body);
+  $table.append($("<tfoot></tfoot>").append(monthTotalRow("TOTAL", report.net)));
+  $list.append($table);
+}
+
+function monthRow(label, value, cls, note) {
+  const $tr = $("<tr></tr>").addClass(cls);
+  const $name = $("<td class='budget-name'></td>").text(label);
+  if (note) $name.append($("<div class='budget-note'></div>").text(note));
+  $tr.append($name, $("<td class='budget-value'></td>").text(money(value)));
+  return $tr;
+}
+
+function monthTotalRow(label, value) {
+  const $tr = $("<tr class='budget-total'></tr>");
+  $tr.append($("<td class='budget-name'></td>").text(label));
+  $tr.append($("<td class='budget-value'></td>").text(money(value)));
+  return $tr;
+}
+
+function subsectionRow(label) {
+  return $("<tr class='budget-subsection'></tr>").append(
+    $("<td colspan='2'></td>").text(label)
+  );
+}
+
 function sectionRow(label) {
  return $("<tr class='budget-section'></tr>").append(
    $("<td colspan='2'></td>").text(label)
@@ -3,16 +3,18 @@
 // city's production queue, so the train tab shows both kinds of order.

 import { groupDigits, hours } from "../../../shared/text_format.js";
-import { ECONOMY, BUILDINGS, EFFECT_BUDGET_INCOME, effectValue } from "../../../shared/data.js";
+import { ECONOMY, BUILDINGS, EFFECT_BUDGET_INCOME, effectValue, resourceById } from "../../../shared/data.js";
+import { constructionResourceCost, formatResourceAmount } from "../../../shared/resources.js";
 import {
  buildingBuildCost,
  buildingRefund,
  buildingUpkeep,
 } from "../../../shared/rules.js";
-import { buildingEffectText, signedMoney } from "./format.js";
+import { buildingEffectText, signedMoney, quotedBuildCost } from "./format.js";
 import { renderBudget } from "./budget.js";
 import { bindTabs } from "./tabs.js";
 import { ethnicityChart } from "../ui/ethnicity.js";
+import { currencySymbol } from "../currency.js";

 export class CityModal {
  constructor() {
@@ -34,6 +36,9 @@ export class CityModal {
    this.$budgetSub = $("#city-budget-sub");
    this.$budgetList = $("#city-budget-list");

+    this.$economySub = $("#city-economy-sub");
+    this.$economyList = $("#city-economy-list");
+
    this.cityId = 0;
    this.gdp = 0;
    this.coastal = false;
@@ -41,6 +46,8 @@ export class CityModal {
    this.constructionSpeed = 0;
    // Local test game: each order also offers a free, instant button.
    this.testing = false;
+    // Today's market prices, so build costs are quoted at current rates.
+    this.prices = {};
    this._levels = {};
    this.protoNames = new Map();
    // Signature of the trainable set currently drawn, so a snapshot that did
@@ -75,6 +82,7 @@ export class CityModal {
    this.coastal = !!view.coastal;
    this.constructionSpeed = view.constructionSpeed || 0;
    this.testing = !!view.testing;
+    this.prices = view.prices || {};
    this.$title.text(`${city.name} — City`);
    this._renderTrainList(this.gdp, view.trainable || []);
    this.renderQueue(view.queue || []);
@@ -87,9 +95,10 @@ export class CityModal {
      base: view.base || 0,
      approval: view.approval,
    });
-    this.$budgetSub.text("Region net  +€0/h");
+    this.$budgetSub.text(`Region net  +${currencySymbol()}0/h`);
    this.renderBudget(null);
    this.renderPeople(view.ethnicMakeup || [], view.approval, view.taxMultiplier, view.civs || []);
+    this.renderEconomy(view.cash || {}, view.cashValue || 0, view.currencies || [], view.debt || 0);
    this.$modal.removeClass("hidden");
  }

@@ -117,6 +126,52 @@ export class CityModal {
    }
  }

+  // The region's private-sector cash: a basket of currencies it holds. Regions
+  // are the game's private economic agents, so this is their own money, not the
+  // government treasury.
+  renderEconomy(cash, cashValue, currencies = [], debt = 0) {
+    if (!this.$economyList || !this.$economyList.length) return;
+    this.$economyList.empty();
+    const byCode = new Map(currencies.map((entry) => [entry.code, entry]));
+    if (this.$economySub && this.$economySub.length) {
+      const owed = debt > 0
+        ? `   ·   Debt: ${currencySymbol()}${groupDigits(Math.round(debt))}`
+        : "";
+      this.$economySub.text(
+        `Private-sector cash: ${currencySymbol()}${groupDigits(Math.round(cashValue || 0))}${owed}`
+      );
+    }
+    this.$economyList.append(
+      $("<div class='desc'></div>").text(
+        "This region is a private economic agent: it holds its own cash reserve, " +
+          "trades with its neighbours and chases profit."
+      )
+    );
+    const holdings = Object.entries(cash || {}).filter(([, amount]) => amount > 0);
+    if (holdings.length === 0) {
+      this.$economyList.append($("<div class='desc'></div>").text("No cash held."));
+      return;
+    }
+    const $table = $("<table class='resources-table economy-table'></table>");
+    const $head = $("<thead></thead>").append(
+      $("<tr></tr>")
+        .append($("<th></th>").text("Currency"))
+        .append($("<th class='numeric'></th>").text("Held"))
+    );
+    const $body = $("<tbody></tbody>");
+    for (const [code, amount] of holdings) {
+      const currency = byCode.get(code);
+      const name = currency ? `${currency.symbol} ${currency.name} (${code})` : code;
+      $body.append(
+        $("<tr></tr>")
+          .append($("<td></td>").text(name))
+          .append($("<td class='numeric'></td>").text(groupDigits(Math.round(amount))))
+      );
+    }
+    $table.append($head, $body);
+    this.$economyList.append($table);
+  }
+
  // -------------------------------------------------------------- training --

  // The fraction of the base build time a construction technology leaves, so a
@@ -125,6 +180,34 @@ export class CityModal {
    return 1 / (1 + (this.constructionSpeed || 0));
  }

+  // The full price of a construction at today's market: the build cost plus its
+  // material bill at current prices, whether or not the city already holds the
+  // materials.
+  _quotedCost(cost, proto, level) {
+    return quotedBuildCost(cost, constructionResourceCost(proto, level, cost), this.prices);
+  }
+
+  // The materials a construction spends, each with its icon, so a unit's cost
+  // reads in resources first and the money figure stays secondary.
+  _resourceCostEl(resources) {
+    const $wrap = $("<span class='train-resources'></span>");
+    for (const id of ["steel", "energy", "hightech"]) {
+      const amount = resources[id] || 0;
+      if (!(amount > 0)) continue;
+      const proto = resourceById(id);
+      $wrap.append(
+        $("<span class='cost-res'></span>").append(
+          $("<img class='cost-icon'>")
+            .attr("src", `assets/${proto.icon}`)
+            .attr("alt", proto.name)
+            .attr("title", proto.name),
+          $("<span></span>").text(formatResourceAmount(id, amount))
+        )
+      );
+    }
+    return $wrap;
+  }
+
  _renderTrainList(gdp, trainableUnits) {
    this.protoNames = new Map();
    this.$trainList.empty();
@@ -140,7 +223,12 @@ export class CityModal {
      }
      const duration = ECONOMY.trainingHours(gdp, proto.cost) * this._constructionTimeFactor();
      button.append(
-        $("<span></span>").text(`${proto.name}  —  Cost ${groupDigits(proto.cost)}  —  ${hours(duration)}`)
+        $("<span class='train-name'></span>").text(proto.name),
+        this._resourceCostEl(constructionResourceCost(proto, 0, proto.cost)),
+        $("<span class='train-price'></span>").text(
+          `${currencySymbol()}${groupDigits(this._quotedCost(proto.cost, proto, 0))}`
+        ),
+        $("<span class='train-time'></span>").text(hours(duration))
      );
      const serverIndex = proto.serverIndex !== undefined ? proto.serverIndex : index;
      signature.push(serverIndex);
@@ -295,13 +383,13 @@ export class CityModal {
    const sign = amount >= 0 ? "+" : "−";
    $button.attr(
      "title",
-      `Expected budget income ${sign}€${groupDigits(Math.round(Math.abs(amount)))}/h`
+      `Expected budget income ${sign}${currencySymbol()}${groupDigits(Math.round(Math.abs(amount)))}/h`
    );
  }

  refreshBuildings(budget, levels, gdp = 0, queued = {}, region = null) {
    this._levels = levels || {};
-    this.$buildingsBudget.text(`Budget: €${groupDigits(Math.round(budget))}`);
+    this.$buildingsBudget.text(`Budget: ${currencySymbol()}${groupDigits(Math.round(budget))}`);
    for (const row of this.buildingRows) {
      const level = levels[row.index] || 0;
      const pending = queued[row.index] || 0;
@@ -312,16 +400,16 @@ export class CityModal {
      row.$name.text(`${row.proto.name}   —   ${levelText}`);
      row.$effects.text(buildingEffectText(row.proto, level > 0 ? level : Math.max(nextLevel, 1)));
      const parts = [];
-      if (level > 0) parts.push(`Upkeep €${groupDigits(Math.round(buildingUpkeep(row.proto, level)))}/h`);
+      if (level > 0) parts.push(`Upkeep ${currencySymbol()}${groupDigits(Math.round(buildingUpkeep(row.proto, level)))}/h`);
      const cost = buildingBuildCost(row.proto, nextLevel);
      const duration = ECONOMY.trainingHours(gdp, cost) * this._constructionTimeFactor();
-      parts.push(`Build cost €${groupDigits(Math.round(cost))} · ${hours(duration)}`);
+      parts.push(`Build cost ${currencySymbol()}${groupDigits(this._quotedCost(cost, row.proto, nextLevel))} · ${hours(duration)}`);
      const requirement = this._buildRequirement(row.proto);
      if (requirement) parts.push(requirement);
      row.$cost.text(parts.join("   ·   "));
      row.$upgrade
-        .text(`Upgrade  €${groupDigits(Math.round(cost))}`)
-        .prop("disabled", !!requirement || budget < cost);
+        .text(`Upgrade  ${currencySymbol()}${groupDigits(this._quotedCost(cost, row.proto, nextLevel))}`)
+        .prop("disabled", !!requirement);
      this._setBuildTooltip(row.$upgrade, row.proto, level, nextLevel + 1, region);
      if (row.$free) {
        // Free does not ignore placement rules (a port still needs the sea).
@@ -332,7 +420,7 @@ export class CityModal {
      }
      if (level > 0) {
        row.$downgrade
-          .text(`Downgrade  +€${groupDigits(Math.round(buildingRefund(row.proto, level)))}`)
+          .text(`Downgrade  +${currencySymbol()}${groupDigits(Math.round(buildingRefund(row.proto, level)))}`)
          .prop("disabled", false);
      } else {
        row.$downgrade.text("Not built").prop("disabled", true);
@@ -2,12 +2,36 @@

 import { groupDigits } from "../../../shared/text_format.js";
 import { policyById } from "../../../shared/data.js";
+import { marketPriceIndex, resourceMarketValue } from "../../../shared/resources.js";
+import { currencySymbol } from "../currency.js";
+
+// The world market's current prices, from the snapshot's market listing.
+export function marketPricesFrom(snapshot) {
+  const prices = {};
+  for (const entry of (snapshot && snapshot.resourceMarket) || []) {
+    prices[entry.id] = entry.price;
+  }
+  return prices;
+}
+
+// A fixed money cost quoted at today's market: a cost with no material bill of
+// its own is scaled by the global price index, so every euro figure drifts with
+// commodity prices.
+export function quotedMoney(amount, prices) {
+  return Math.round((amount || 0) * marketPriceIndex(prices));
+}
+
+// A construction's full price at today's market: the fixed build cost plus the
+// market value of its whole material bill, ignoring anything already in store.
+export function quotedBuildCost(buildCost, materials, prices) {
+  return Math.round((buildCost || 0) + resourceMarketValue(materials, prices));
+}

 export function formatEffect(effect, level) {
  const value = level <= 0 ? 0 : effect.baseValue * Math.pow(level, effect.exponent);
  switch (effect.stat) {
-    case "gdp":
-      return `${value >= 0 ? "+" : ""}${(value * 100).toFixed(1)}% GDP/capita`;
+    case "production":
+      return `${value >= 0 ? "+" : ""}${(value * 100).toFixed(1)}% production`;
    case "budget_income":
      return `${value >= 0 ? "+" : ""}${(value * 100).toFixed(1)}% tax income`;
    case "research":
@@ -49,9 +73,12 @@ export function buildingEffectText(proto, level) {
    }
    case "air_defense":
      return "Fires one volley at hostile aircraft over the city";
-    case "port_gdp": {
-      const per = (proto.gdpPerCapitaPerSeaTilePerLevel || 0) * level;
-      return `+${groupDigits(per)} GDP/capita per adjacent sea tile to the region`;
+    case "port_production": {
+      const per = (proto.productionPerSeaTilePerLevel || 0) * level;
+      const food = (proto.foodPerSeaTilePerLevel || 0) * level * 100;
+      const parts = [`+${groupDigits(per)} production per person per adjacent sea tile to the region`];
+      if (food > 0) parts.push(`+${food.toFixed(1)}% food output per adjacent sea tile`);
+      return parts.join("   ·   ");
    }
    case "air_immigration":
      return "Immigration from every other city with an airport";
@@ -63,7 +90,12 @@ export function buildingEffectText(proto, level) {
 export const SOURCE_LABELS = { building: "building", government: "government", technology: "research" };

 export function signedMoney(value) {
-  return `${value < 0 ? "−" : "+"}€${groupDigits(Math.round(Math.abs(value)))}/h`;
+  return `${value < 0 ? "−" : "+"}${currencySymbol()}${groupDigits(Math.round(Math.abs(value)))}/h`;
+}
+
+// A signed money amount with no period suffix, for the monthly budget report.
+export function money(value) {
+  return `${value < 0 ? "−" : "+"}${currencySymbol()}${groupDigits(Math.round(Math.abs(value)))}`;
 }

 export function percent(value) {
@@ -5,11 +5,13 @@ import {
  governmentChangeCost,
  prerequisitesMet,
 } from "../../../shared/rules.js";
-import { POLICIES, PROPAGANDA, policyById, TECH_THEMES, technologyCost } from "../../../shared/data.js";
-import { renderBudget } from "./budget.js";
-import { effectsText, signedMoney } from "./format.js";
+import { POLICIES, PROPAGANDA, policyById, TECH_THEMES, technologyCost, RESOURCES } from "../../../shared/data.js";
+import { formatResourceAmount } from "../../../shared/resources.js";
+import { renderMonthlyBudget } from "./budget.js";
+import { effectsText, money, quotedMoney } from "./format.js";
 import { bindTabs } from "./tabs.js";
 import { ethnicityChart } from "../ui/ethnicity.js";
+import { currencySymbol } from "../currency.js";

 export class NationModal {
  constructor() {
@@ -19,7 +21,25 @@ export class NationModal {
    this.$technologySub = $("#technology-sub");
    this.$technologyList = $("#technology-list");
    this.$budgetSub = $("#budget-sub");
+    this.$budgetMonths = $("#budget-months");
    this.$budgetList = $("#budget-list");
+    this.$economySub = $("#economy-sub");
+    this.$economySubtabs = $("#economy-subtabs");
+    this.$economySummary = $("#economy-summary");
+    this.$economyCentralBank = $("#economy-central-bank");
+    this.$economyRates = $("#economy-rates");
+    // Which Economy sub-tab is open: the private sector, the central bank or
+    // the exchange rates.
+    this.economyView = "summary";
+    // The central-bank interest input is built once and only its value updated,
+    // so typing is not interrupted by the snapshot refresh.
+    this._centralBankBuilt = false;
+    this.$resourcesSub = $("#resources-sub");
+    this.$resourcesList = $("#resources-list");
+    this.$resourceTradeList = $("#resource-trade-list");
+    // Which Resources sub-tab is open: the nation's own stores and trade, or
+    // the world ranking of each commodity's major exporter and importer.
+    this.resourceView = "stores";
    this.$diplomacySub = $("#diplomacy-sub");
    this.$diplomacyList = $("#diplomacy-list");
    this.$citiesSub = $("#cities-sub");
@@ -43,9 +63,12 @@ export class NationModal {
    // Conflict cards the player expanded, keyed "a:b". Snapshot refreshes
    // rebuild the list, so the open/closed state has to live outside the DOM.
    this.expandedConflicts = new Set();
-    // Building types whose per-city budget breakdown is expanded.
-    this.expandedBudgetGroups = new Set();
-    this._lastBreakdown = {};
+    // How many months back the budget tab is paging: 0 is the current month.
+    this.budgetOffset = 0;
+    this._treasury = 0;
+    this._budgetMonths = [];
+    // Expense categories whose per-resource purchase detail is expanded.
+    this.expandedBudgetCategories = new Set();
    this.politics = null;
    // The Politics tab is built once and only its lists are refreshed, so the
    // wizard and dropdowns survive the snapshots that arrive while it is open.
@@ -61,6 +84,7 @@ export class NationModal {
    this.onSetCampaignSpending = () => {};
    this.onPolicy = () => {};
    this.onRevokePolicy = () => {};
+    this.onSetInterestRate = () => {};
    this.onConfirm = () => {};
    this.$modal.find(".modal-close").on("click", () => this.close());
    bindTabs(this.$modal, "tab-");
@@ -70,12 +94,32 @@ export class NationModal {
    return !this.$modal.hasClass("hidden");
  }

-  show(governments, currentGovernment, technologies, researched, gdp, budget, researchRate, finances, diplomacy = null, conflicts = [], politics = null, techInfo = null) {
+  // Today's world market prices, from the Resources tab's data. Used to quote
+  // the money costs that carry no material bill of their own.
+  _prices() {
+    if (this.resources && this.resources.summary && this.resources.summary.prices) {
+      return this.resources.summary.prices;
+    }
+    const prices = {};
+    for (const entry of (this.resources && this.resources.market) || []) {
+      prices[entry.id] = entry.price;
+    }
+    return prices;
+  }
+
+  // A fixed money cost quoted at today's market.
+  _quoted(amount) {
+    return quotedMoney(amount, this._prices());
+  }
+
+  show(governments, currentGovernment, technologies, researched, gdp, budget, researchRate, finances, diplomacy = null, conflicts = [], politics = null, techInfo = null, resourcesInfo = null, moneyInfo = null) {
    this.governments = governments;
    this.technologies = technologies;
    this.diplomacy = diplomacy;
    this.conflicts = conflicts || [];
    this.politics = politics;
+    this.resources = resourcesInfo;
+    this.money = moneyInfo;
    // Rebuild the rows from scratch: reopening the panel must not stack a
    // second set of buttons on top of the previous one, or the stale rows keep
    // their old labels and disabled state and appear unresponsive.
@@ -84,7 +128,9 @@ export class NationModal {
    this.governmentRows = governments.map((proto, index) => this._makeRow(this.$governmentList, proto, index, "government"));
    this.technologyRows = technologies.map((proto, index) => this._makeRow(this.$technologyList, proto, index, "technology"));
    this._buildTechnologyThemes();
-    this.refresh(currentGovernment, researched, gdp, budget, researchRate, finances, diplomacy, conflicts, politics, techInfo);
+    this._buildResourceSubtabs();
+    this._buildEconomySubtabs();
+    this.refresh(currentGovernment, researched, gdp, budget, researchRate, finances, diplomacy, conflicts, politics, techInfo, resourcesInfo, moneyInfo);
    this.$modal.removeClass("hidden");
  }

@@ -113,18 +159,282 @@ export class NationModal {
    }
  }

-  // The national budget, drawn by the shared table renderer. Building types
-  // expand to their per-city cost.
-  _renderBudget(breakdown) {
+  // The Resources tab's sub-tabs: the nation's own stores and trade, and the
+  // world ranking of each commodity's major exporters and importers. Both views
+  // are rendered together; switching only shows and hides them.
+  _buildResourceSubtabs() {
+    const $tabs = $("#resources-subtabs");
+    if (!$tabs.length) return;
+    $tabs.empty();
+    const views = [
+      { id: "stores", label: "Stores & trade" },
+      { id: "leaders", label: "Major traders" },
+    ];
+    for (const view of views) {
+      const $button = $("<button type='button' class='subtab'></button>")
+        .attr("data-view", view.id)
+        .text(view.label);
+      if (view.id === this.resourceView) $button.addClass("active");
+      $button.on("click", () => this._setResourceView(view.id));
+      $tabs.append($button);
+    }
+  }
+
+  _setResourceView(view) {
+    this.resourceView = view;
+    const $tabs = $("#resources-subtabs");
+    $tabs.find(".subtab").removeClass("active");
+    $tabs.find(`.subtab[data-view="${view}"]`).addClass("active");
+    if (this.$resourcesList) this.$resourcesList.toggleClass("hidden", view !== "stores");
+    if (this.$resourceTradeList) this.$resourceTradeList.toggleClass("hidden", view !== "leaders");
+  }
+
+  // The Economy tab's sub-tabs: the private sector, the central bank and the
+  // exchange-rate table.
+  _buildEconomySubtabs() {
+    if (!this.$economySubtabs || !this.$economySubtabs.length) return;
+    this.$economySubtabs.empty();
+    const views = [
+      { id: "summary", label: "Private sector" },
+      { id: "centralbank", label: "Central bank" },
+      { id: "rates", label: "Exchange rates" },
+    ];
+    for (const view of views) {
+      const $button = $("<button type='button' class='subtab'></button>")
+        .attr("data-view", view.id)
+        .text(view.label);
+      if (view.id === this.economyView) $button.addClass("active");
+      $button.on("click", () => this._setEconomyView(view.id));
+      this.$economySubtabs.append($button);
+    }
+    this._setEconomyView(this.economyView);
+  }
+
+  _setEconomyView(view) {
+    this.economyView = view;
+    if (this.$economySubtabs) {
+      this.$economySubtabs.find(".subtab").removeClass("active");
+      this.$economySubtabs.find(`.subtab[data-view="${view}"]`).addClass("active");
+    }
+    if (this.$economySummary) this.$economySummary.toggleClass("hidden", view !== "summary");
+    if (this.$economyCentralBank) {
+      this.$economyCentralBank.toggleClass("hidden", view !== "centralbank");
+    }
+    if (this.$economyRates) this.$economyRates.toggleClass("hidden", view !== "rates");
+    // Render the view that just became visible.
+    this._renderEconomy(this.money);
+  }
+
+  _renderEconomy(money) {
+    this.money = money || this.money || {};
+    if (this.economyView === "centralbank") this._renderCentralBank(this.money);
+    else if (this.economyView === "rates") this._renderExchangeRates(this.money);
+    else this._renderPrivateSector(this.money);
+  }
+
+  // The aggregate private-sector cash the nation's regions hold, and each
+  // region's own reserve.
+  _renderPrivateSector(money) {
+    if (!this.$economySummary || !this.$economySummary.length) return;
+    const cash = money.privateCash || 0;
+    if (this.$economySub && this.$economySub.length) {
+      this.$economySub.text(
+        `Private-sector money: ${currencySymbol()}${groupDigits(Math.round(cash))}   ·   ` +
+        `${(money.currency && money.currency.name) || ""}`
+      );
+    }
+    this.$economySummary.empty();
+    this.$economySummary.append(
+      $("<div class='desc'></div>").text(
+        "Regions are private economic agents: each holds its own cash reserve, " +
+        "trades with its neighbours and chases profit."
+      )
+    );
+    const cities = (money.cities || []).filter((city) => city.civ === money.viewerCiv);
+    if (cities.length === 0) return;
+    const $table = $("<table class='resources-table economy-table'></table>");
+    const $head = $("<thead></thead>").append(
+      $("<tr></tr>")
+        .append($("<th></th>").text("Region"))
+        .append($("<th class='numeric'></th>").text("Private cash"))
+    );
+    const $body = $("<tbody></tbody>");
+    let total = 0;
+    for (const city of cities) {
+      total += city.cashValue || 0;
+      $body.append(
+        $("<tr></tr>")
+          .append($("<td></td>").text(city.name))
+          .append(
+            $("<td class='numeric'></td>").text(
+              `${currencySymbol()}${groupDigits(Math.round(city.cashValue || 0))}`
+            )
+          )
+      );
+    }
+    $table.append($head, $body);
+    const $foot = $("<tfoot></tfoot>").append(
+      $("<tr class='budget-total'></tr>")
+        .append($("<td></td>").text("Total"))
+        .append($("<td class='numeric'></td>").text(
+          `${currencySymbol()}${groupDigits(Math.round(total))}`
+        ))
+    );
+    $table.append($foot);
+    this.$economySummary.append($table);
+  }
+
+  // The central bank: its interest rate, which compounds into every region's
+  // private cash, and the foreign reserves it has accumulated.
+  _renderCentralBank(money) {
+    if (!this.$economyCentralBank || !this.$economyCentralBank.length) return;
+    const bank = money.centralBank || { rate: 0, reserves: [] };
+    if (this.$economySub && this.$economySub.length) {
+      this.$economySub.text(
+        `${(money.currency && money.currency.name) || "Central bank"}   ·   ` +
+        `Interest rate ${(bank.rate * 100).toFixed(2)}%/year`
+      );
+    }
+    if (!this._centralBankBuilt) {
+      this.$economyCentralBank.empty();
+      const $rate = $("<div class='central-bank-rate'></div>");
+      $rate.append($("<label for='cb-rate'></label>").text("Interest rate (% per year)"));
+      const $input = $("<input id='cb-rate' type='number' min='0' max='50' step='0.25'>");
+      const $apply = $("<button type='button' class='aero cb-apply'></button>").text("Set");
+      const apply = () => {
+        const percent = Number($input.val());
+        if (!Number.isFinite(percent) || percent < 0) return;
+        this.onSetInterestRate(percent / 100);
+      };
+      $apply.on("click", apply);
+      $input.on("keydown", (event) => {
+        if (event.key === "Enter") apply();
+      });
+      $rate.append($input, $apply);
+      this.$economyCentralBank.append($rate);
+      this.$economyCentralBank.append(
+        $("<div class='desc'></div>").text(
+          "Regions borrow from the bank at this rate when their cash runs out, " +
+          "and it compounds on whatever they owe. The government may run an " +
+          "overdraft here too."
+        )
+      );
+      this.$economyCentralBank.append($("<div class='central-bank-loans'></div>"));
+      const $reserves = $("<div class='central-bank-reserves'></div>");
+      this.$economyCentralBank.append($reserves);
+      this._centralBankBuilt = true;
+    }
+    const $input = this.$economyCentralBank.find("#cb-rate");
+    if ($input.length && document.activeElement !== $input.get(0)) {
+      $input.val((bank.rate * 100).toFixed(2));
+    }
+    this.$economyCentralBank.find(".central-bank-loans").text(
+      `Outstanding loans: ${currencySymbol()}${groupDigits(Math.round(bank.loans || 0))}`
+    );
+    const $reserves = this.$economyCentralBank.find(".central-bank-reserves");
+    $reserves.empty();
+    $reserves.append($("<div class='subhead'></div>").text("Foreign reserves"));
+    if ((bank.reserves || []).length === 0) {
+      $reserves.append($("<div class='desc'></div>").text("No foreign currency held yet."));
+      return;
+    }
+    const $table = $("<table class='resources-table economy-table'></table>");
+    const $body = $("<tbody></tbody>");
+    for (const reserve of bank.reserves) {
+      $body.append(
+        $("<tr></tr>")
+          .append($("<td></td>").text(`${reserve.symbol} ${reserve.name}`))
+          .append(
+            $("<td class='numeric'></td>").text(
+              groupDigits(Math.round(reserve.amount || 0))
+            )
+          )
+      );
+    }
+    $table.append($body);
+    $reserves.append($table);
+  }
+
+  // The exchange rate between the viewer's currency and every other.
+  _renderExchangeRates(money) {
+    if (!this.$economyRates || !this.$economyRates.length) return;
+    const mine = money.currency || { name: "Currency" };
+    if (this.$economySub && this.$economySub.length) {
+      this.$economySub.text(`Exchange rates against the ${mine.name}`);
+    }
+    this.$economyRates.empty();
+    const rows = money.exchangeRates || [];
+    const $table = $("<table class='resources-table economy-table'></table>");
+    const $head = $("<thead></thead>").append(
+      $("<tr></tr>")
+        .append($("<th></th>").text("Currency"))
+        .append($("<th class='numeric'></th>").text(`1 ${mine.code || ""} buys`))
+    );
+    const $body = $("<tbody></tbody>");
+    for (const entry of rows) {
+      $body.append(
+        $("<tr></tr>")
+          .append($("<td></td>").text(`${entry.symbol} ${entry.name} (${entry.code})`))
+          .append($("<td class='numeric'></td>").text(entry.rate.toFixed(4)))
+      );
+    }
+    $table.append($head, $body);
+    this.$economyRates.append($table);
+  }
+
+  // The national budget: the selected month's actual income and expenses, with
+  // a pager back through the stored monthly digests. The treasury stays on the
+  // subtitle so the table is purely the month's flows.
+  _renderBudget(finances) {
    if (!this.$budgetList || !this.$budgetList.length) return;
-    this._lastBreakdown = breakdown || {};
-    renderBudget(this.$budgetList, this._lastBreakdown, {
-      expanded: this.expandedBudgetGroups,
-      onToggle: () => this._renderBudget(this._lastBreakdown),
-      showUnits: true,
+    const months = (finances && finances.months) || [];
+    this._budgetMonths = months;
+    const maxOffset = Math.max(0, months.length - 1);
+    if (this.budgetOffset > maxOffset) this.budgetOffset = maxOffset;
+    if (this.budgetOffset < 0) this.budgetOffset = 0;
+    const index = months.length - 1 - this.budgetOffset;
+    const report = index >= 0 ? months[index] : null;
+    this._renderBudgetMonthsNav(months, index);
+    if (this.$budgetSub && this.$budgetSub.length) {
+      const net = report ? `   ·   ${report.label}: ${money(report.net)}` : "";
+      this.$budgetSub.text(`Treasury: ${currencySymbol()}${groupDigits(Math.round(this._treasury))}${net}`);
+    }
+    renderMonthlyBudget(this.$budgetList, report, {
+      expanded: this.expandedBudgetCategories,
+      onToggle: () => this._renderBudget({ months }),
    });
  }

+  _renderBudgetMonthsNav(months, index) {
+    if (!this.$budgetMonths || !this.$budgetMonths.length) return;
+    this.$budgetMonths.empty();
+    if (months.length === 0) return;
+    const older = this.budgetOffset < months.length - 1;
+    const newer = this.budgetOffset > 0;
+    const $prev = $("<button type='button' class='budget-month-nav'></button>")
+      .text("◀")
+      .prop("disabled", !older)
+      .on("click", () => {
+        if (!older) return;
+        this.budgetOffset += 1;
+        this._renderBudget({ months });
+      });
+    const $next = $("<button type='button' class='budget-month-nav'></button>")
+      .text("▶")
+      .prop("disabled", !newer)
+      .on("click", () => {
+        if (!newer) return;
+        this.budgetOffset -= 1;
+        this._renderBudget({ months });
+      });
+    const label = months[index] ? months[index].label : "";
+    this.$budgetMonths.append(
+      $prev,
+      $("<span class='budget-month-label'></span>").text(label),
+      $next
+    );
+  }
+
  // The nation's regions: each city's population, GDP and the tax it collects.
  _renderCities(cities) {
    if (!this.$citiesList || !this.$citiesList.length) return;
@@ -170,8 +480,8 @@ export class NationModal {
      const $name = $("<td class='name'></td>").text(city.isCapital ? `★ ${city.name}` : city.name);
      $tr.append($name);
      $tr.append($("<td class='numeric'></td>").text(compact(city.population)));
-      $tr.append($("<td class='numeric'></td>").text(`€${compact(city.gdp)}`));
-      $tr.append($("<td class='numeric income'></td>").text(`+€${compact(city.income)}`));
+      $tr.append($("<td class='numeric'></td>").text(`${currencySymbol()}${compact(city.gdp)}`));
+      $tr.append($("<td class='numeric income'></td>").text(`+${currencySymbol()}${compact(city.income)}`));
      $body.append($tr);
    }
    $table.append($head, $body);
@@ -180,13 +490,201 @@ export class NationModal {
        $("<tr class='budget-total'></tr>")
          .append($("<td></td>").text("TOTAL"))
          .append($("<td class='numeric'></td>").text(compact(totalPopulation)))
-          .append($("<td class='numeric'></td>").text(`€${compact(totalGdp)}`))
-          .append($("<td class='numeric income'></td>").text(`+€${compact(totalIncome)}`))
+          .append($("<td class='numeric'></td>").text(`${currencySymbol()}${compact(totalGdp)}`))
+          .append($("<td class='numeric income'></td>").text(`+${currencySymbol()}${compact(totalIncome)}`))
      )
    );
    this.$citiesList.append($table);
  }

+  // The Resources tab: the nation's stores, what it consumes and makes, what it
+  // imports and exports, beside the global market's price and the world's supply
+  // and demand. Energy is a daily flow, so it has no store: its row reads the
+  // cities' demand against the power plants' output instead.
+  _renderResources(info) {
+    if (!this.$resourcesList || !this.$resourcesList.length) return;
+    this.$resourcesList.empty();
+    const summary = info && info.summary;
+    if (this.$resourcesSub && this.$resourcesSub.length) {
+      this.$resourcesSub.text(
+        "Stores, daily consumption, production and cross-nation trade, with the " +
+          "global market's price. Energy is delivered as a flow and cannot be stored."
+      );
+    }
+    if (!summary) {
+      this.$resourcesList.append($("<div class='desc'></div>").text("No resource data."));
+    } else {
+      this._renderResourceStores(info, summary);
+    }
+    this._renderResourceLeaders(info);
+    this._setResourceView(this.resourceView);
+  }
+
+  _renderResourceStores(info, summary) {
+    const market = new Map(((info && info.market) || []).map((entry) => [entry.id, entry]));
+    const trade = summary.trade || { imports: {}, exports: {} };
+    const $table = $("<table class='diplomacy-table budget-table resources-table'></table>");
+    const columns = [
+      { label: "Resource" },
+      { label: "Stored", numeric: true },
+      { label: "Consumed / day", numeric: true },
+      { label: "Made / day", numeric: true },
+      { label: "Exported / day", numeric: true },
+      { label: "Imported / day", numeric: true },
+      { label: "Market price", numeric: true },
+      { label: "World supply / day", numeric: true },
+      { label: "World demand / day", numeric: true },
+    ];
+    const $head = $("<thead></thead>");
+    const $headRow = $("<tr></tr>");
+    for (const column of columns) {
+      const $th = $("<th></th>").text(column.label);
+      if (column.numeric) $th.addClass("numeric");
+      $headRow.append($th);
+    }
+    $head.append($headRow);
+    const $body = $("<tbody></tbody>");
+    for (const proto of RESOURCES) {
+      const energy = proto.id === "energy";
+      const stats = market.get(proto.id) || {};
+      const stored = energy ? "—" : formatResourceAmount(proto.id, summary.stock[proto.id] || 0);
+      const consumed = energy
+        ? formatResourceAmount("energy", (summary.consumed && summary.consumed.energy) || 0)
+        : formatResourceAmount(proto.id, (summary.consumed && summary.consumed[proto.id]) || 0);
+      const made = energy
+        ? formatResourceAmount("energy", summary.energy ? summary.energy.supply : 0)
+        : formatResourceAmount(proto.id, summary.production[proto.id] || 0);
+      const exported = formatResourceAmount(
+        proto.id,
+        (trade.exports && trade.exports[proto.id]) || 0
+      );
+      const imported = formatResourceAmount(
+        proto.id,
+        (trade.imports && trade.imports[proto.id]) || 0
+      );
+      const $tr = $("<tr></tr>");
+      const $name = $("<td class='name'></td>");
+      $name.append(
+        $("<img class='resource-icon' width='18' height='18'>")
+          .attr("src", `assets/${proto.icon}`)
+          .attr("alt", proto.name)
+      );
+      $name.append($("<span></span>").text(` ${proto.name}`));
+      $tr.append($name);
+      $tr.append($("<td class='numeric'></td>").text(stored));
+      $tr.append($("<td class='numeric'></td>").text(consumed));
+      $tr.append($("<td class='numeric'></td>").text(made));
+      $tr.append($("<td class='numeric'></td>").text(exported));
+      $tr.append($("<td class='numeric'></td>").text(imported));
+      $tr.append($("<td class='numeric'></td>").text(this._resourcePriceText(proto, stats.price)));
+      $tr.append(
+        $("<td class='numeric'></td>").text(
+          formatResourceAmount(proto.id, Math.max(0, stats.supply || 0))
+        )
+      );
+      $tr.append(
+        $("<td class='numeric'></td>").text(
+          formatResourceAmount(proto.id, Math.max(0, stats.demand || 0))
+        )
+      );
+      $body.append($tr);
+    }
+    $table.append($head, $body);
+    this.$resourcesList.append($table);
+    this.$resourcesList.append(
+      $("<div class='desc'></div>").text(
+        "Consumption is the people's needs plus the materials buildings, units and works " +
+          "wear out. Exports and imports count yesterday's deliveries between nations; the " +
+          "global market is not a partner. Prices drift with the world's supply and demand, " +
+          "and a city buys from the cheapest source it can reach, then from the market."
+      )
+    );
+  }
+
+  // The Major traders sub-tab: for every commodity, the nation that exported the
+  // most over the last day and the one that imported the most.
+  _renderResourceLeaders(info) {
+    if (!this.$resourceTradeList || !this.$resourceTradeList.length) return;
+    this.$resourceTradeList.empty();
+    const trade = (info && info.trade) || [];
+    const civs = (info && info.civs) || [];
+    const name = (civ) => (civs[civ] ? civs[civ].name : `Nation ${civ + 1}`);
+    const $table = $("<table class='diplomacy-table budget-table resources-table'></table>");
+    const columns = [
+      { label: "Resource" },
+      { label: "Major exporter" },
+      { label: "Exported / day", numeric: true },
+      { label: "Major importer" },
+      { label: "Imported / day", numeric: true },
+    ];
+    const $head = $("<thead></thead>");
+    const $headRow = $("<tr></tr>");
+    for (const column of columns) {
+      const $th = $("<th></th>").text(column.label);
+      if (column.numeric) $th.addClass("numeric");
+      $headRow.append($th);
+    }
+    $head.append($headRow);
+    const $body = $("<tbody></tbody>");
+    for (const proto of RESOURCES) {
+      const best = (kind) => {
+        let winner = null;
+        for (const entry of trade) {
+          const amount = (entry[kind] && entry[kind][proto.id]) || 0;
+          if (amount > 0 && (!winner || amount > winner.amount)) {
+            winner = { civ: entry.civ, amount };
+          }
+        }
+        return winner;
+      };
+      const exporter = best("exports");
+      const importer = best("imports");
+      const $tr = $("<tr></tr>");
+      const $name = $("<td class='name'></td>");
+      $name.append(
+        $("<img class='resource-icon' width='18' height='18'>")
+          .attr("src", `assets/${proto.icon}`)
+          .attr("alt", proto.name)
+      );
+      $name.append($("<span></span>").text(` ${proto.name}`));
+      $tr.append($name);
+      $tr.append($("<td></td>").text(exporter ? name(exporter.civ) : "—"));
+      $tr.append(
+        $("<td class='numeric'></td>").text(
+          exporter ? formatResourceAmount(proto.id, exporter.amount) : "—"
+        )
+      );
+      $tr.append($("<td></td>").text(importer ? name(importer.civ) : "—"));
+      $tr.append(
+        $("<td class='numeric'></td>").text(
+          importer ? formatResourceAmount(proto.id, importer.amount) : "—"
+        )
+      );
+      $body.append($tr);
+    }
+    $table.append($head, $body);
+    this.$resourceTradeList.append($table);
+    this.$resourceTradeList.append(
+      $("<div class='desc'></div>").text(
+        "The largest cross-nation deliveries of the last day, in each resource. " +
+          "Only trade between nations is counted, so goods bought from the global " +
+          "market never make a nation an importer here."
+      )
+    );
+  }
+
+  // A market price reads in euro per the resource's own unit; tiny energy prices
+  // keep enough decimals to be legible.
+  _resourcePriceText(proto, price) {
+    const value = price === undefined || price === null ? 0 : price;
+    const text = value >= 1000
+      ? groupDigits(Math.round(value))
+      : value >= 1
+        ? value.toFixed(0)
+        : value.toFixed(4);
+    return `${currencySymbol()}${text} / ${proto.unit}`;
+  }
+
  _makeRow($list, proto, index, kind) {
    const $card = $("<div class='row-card'></div>");
    const $info = $("<div class='info'></div>");
@@ -207,29 +705,29 @@ export class NationModal {
    return { proto, index, kind, $name, $effects, $cost, $action, $card };
  }

-  refresh(currentGovernment, researched, gdp, budget, researchRate, finances = {}, diplomacy = null, conflicts = null, politics = null, techInfo = null) {
+  refresh(currentGovernment, researched, gdp, budget, researchRate, finances = {}, diplomacy = null, conflicts = null, politics = null, techInfo = null, resourcesInfo = null, moneyInfo = null) {
    this.currentGovernment = currentGovernment;
    if (techInfo) this.techInfo = techInfo;
+    if (resourcesInfo) this.resources = resourcesInfo;
    this.researched = researched instanceof Set ? researched : new Set(Object.keys(researched).map(Number));
    if (diplomacy !== null) this.diplomacy = diplomacy;
    if (conflicts !== null) this.conflicts = conflicts || [];
    if (politics !== null) this.politics = politics;
    this.$governmentSub.text(
-      `Government — ${this.governments[currentGovernment] ? this.governments[currentGovernment].name : "None"}   ·   Budget: €${groupDigits(Math.round(budget))}`
+      `Government — ${this.governments[currentGovernment] ? this.governments[currentGovernment].name : "None"}   ·   Budget: ${currencySymbol()}${groupDigits(Math.round(budget))}`
    );
    // Research has no pool: every point flows into the focused technology, so
    // the panel shows the rate instead of a stockpile.
    this.$technologySub.text(`Research: +${(researchRate || 0).toFixed(1)}/h`);

-    const breakdown = finances || {};
-    const net = breakdown.net || 0;
+    const fin = finances || {};
+    this._treasury = budget;

-    this.$budgetSub.text(
-      `Treasury: €${groupDigits(Math.round(budget))}   ·   Net: ${signedMoney(net)}`
-    );
-
-    this._renderBudget(breakdown);
-    this._renderCities(breakdown.cities);
+    if (moneyInfo) this.money = moneyInfo;
+    this._renderBudget(fin);
+    this._renderCities(fin.cities);
+    this._renderResources(this.resources);
+    this._renderEconomy(this.money);

    for (const row of this.governmentRows) {
      const proto = row.proto;
@@ -240,8 +738,10 @@ export class NationModal {
        row.$action.text("Current government").prop("disabled", true);
      } else {
        const cost = governmentChangeCost(proto, gdp);
-        row.$cost.text(`Adoption cost €${groupDigits(Math.round(cost))}`);
-        row.$action.text(`Adopt  €${groupDigits(Math.round(cost))}`).prop("disabled", budget < cost);
+        row.$cost.text(`Adoption cost ${currencySymbol()}${groupDigits(this._quoted(cost))}`);
+        row.$action
+          .text(`Adopt  ${currencySymbol()}${groupDigits(this._quoted(cost))}`)
+          .prop("disabled", false);
      }
    }

@@ -370,8 +870,8 @@ export class NationModal {
      const $tr = $("<tr></tr>");
      if (row.self) $tr.addClass("local-nation");
      $tr.append($("<td class='name'></td>").text(row.name));
-      $tr.append($("<td class='numeric'></td>").text(`€${compact(row.gdp)}`));
-      $tr.append($("<td class='numeric'></td>").text(`€${compact(row.gdpPerCapita)}`));
+      $tr.append($("<td class='numeric'></td>").text(`${currencySymbol()}${compact(row.gdp)}`));
+      $tr.append($("<td class='numeric'></td>").text(`${currencySymbol()}${compact(row.gdpPerCapita)}`));
      $tr.append($("<td class='numeric'></td>").text(compact(row.population)));
      $tr.append($("<td class='numeric'></td>").text(`${Math.round(row.approval * 100)}%`));
      const $status = $("<td class='status'></td>");
@@ -604,7 +1104,7 @@ export class NationModal {
    const spent = hourly * activeHours;
    const days = Math.floor(activeHours / 24);
    return (
-      `€${groupDigits(hourly)}/h  ·  €${groupDigits(Math.round(spent))} spent over ` +
+      `${currencySymbol()}${groupDigits(this._quoted(hourly))}/h  ·  ${currencySymbol()}${groupDigits(Math.round(spent))} spent over ` +
      `${days} day${days === 1 ? "" : "s"}`
    );
  }
@@ -632,10 +1132,10 @@ export class NationModal {
        value: campaign.hourlyCost,
      });
      const $spend = $("<span class='politics-readout'></span>").text(
-        `€${groupDigits(campaign.hourlyCost)}/h`
+        `${currencySymbol()}${groupDigits(this._quoted(campaign.hourlyCost))}/h`
      );
      $slider.on("input", () =>
-        $spend.text(`€${groupDigits(Number($slider.val()))}/h`)
+        $spend.text(`${currencySymbol()}${groupDigits(this._quoted(Number($slider.val())))}/h`)
      );
      $slider.on("change", () => {
        const amount = Number($slider.val());
@@ -643,10 +1143,10 @@ export class NationModal {
          // Reverting to the last known spend keeps the control honest until
          // the player confirms the stop.
          $slider.val(campaign.hourlyCost);
-          $spend.text(`€${groupDigits(campaign.hourlyCost)}/h`);
+          $spend.text(`${currencySymbol()}${groupDigits(this._quoted(campaign.hourlyCost))}/h`);
          this.onConfirm(
            "Stop this campaign?",
-            "Cutting the spending to €0 will stop the campaign.",
+            `Cutting the spending to ${currencySymbol()}0 will stop the campaign.`,
            () => this.onCancelCampaign(campaign.id)
          );
        } else {
@@ -683,7 +1183,7 @@ export class NationModal {
    );
    $card.append(
      $("<div class='desc politics-cost'></div>").text(
-        `Costs €${groupDigits(PROPAGANDA.defaultHourlyCost)}/h to begin; ` +
+        `Costs ${currencySymbol()}${groupDigits(this._quoted(PROPAGANDA.defaultHourlyCost))}/h to begin; ` +
          "adjust the spending on an active campaign to make it land harder or softer."
      )
    );
@@ -0,0 +1,244 @@
+// Headless resource-economy simulation, used to tune the costs in
+// shared/data/resources.js. It boots a game, optionally raises a fixed set of
+// resource buildings for every nation, runs a number of in-game days and prints
+// how the economy settles: what each nation spends on power and goods, whether
+// its people are fed, and how each producer's build cost pays back at market
+// prices.
+//
+//   node scripts/simulate_resources.js
+//   node scripts/simulate_resources.js --days 720 --civs 2 --scenario infra
+//   node scripts/simulate_resources.js --map full --days 365 --civs 6
+
+import { GameState } from "../shared/game_state.js";
+import { CIVILISATIONS, MAP_CONFIG } from "../shared/data.js";
+import { RESOURCE_BUILDINGS, RESOURCE_RULES, RESOURCE_MARKET_BASE } from "../shared/data/resources.js";
+import {
+  cityEnergyPerDay,
+  foodNeedPerDay,
+  steelNeedPerDay,
+  luxuryNeedPerDay,
+} from "../shared/resources.js";
+import { key } from "../shared/hex.js";
+
+const args = parseArgs(process.argv.slice(2));
+const DAYS = Number(args.days || 360);
+const CIVS = Number(args.civs || 2);
+const SCENARIO = args.scenario || "baseline";
+const MAP = args.map || "medium";
+const seed = Number(args.seed || 12345);
+
+const state = new GameState();
+state.mapConfig = mapConfig(MAP);
+const civs = CIVILISATIONS.slice(0, Math.max(1, Math.min(CIVS, CIVILISATIONS.length)));
+state.configure(civs, seed);
+
+if (SCENARIO === "infra") seedInfrastructure(state);
+if (SCENARIO === "developed") seedBuildings(state);
+
+const startBudget = civs.map((_, civ) => state.getBudget(civ));
+const spendTotals = civs.map(() => ({ energy: 0, goods: 0, transport: 0, construction: 0, upkeep: 0, combat: 0 }));
+
+for (let day = 0; day < DAYS; day++) {
+  for (let hour = 0; hour < 24; hour++) state.advanceHour();
+  for (let civ = 0; civ < civs.length; civ++) {
+    const record = state.resourceSpend.get(civ) || {};
+    for (const kind of Object.keys(spendTotals[civ])) {
+      spendTotals[civ][kind] += record[kind] || 0;
+    }
+  }
+}
+
+// ---------------------------------------------------------------------------
+
+function parseArgs(list) {
+  const out = {};
+  for (let i = 0; i < list.length; i++) {
+    const item = list[i];
+    if (!item.startsWith("--")) continue;
+    const name = item.slice(2);
+    const next = list[i + 1];
+    if (next === undefined || next.startsWith("--")) out[name] = true;
+    else {
+      out[name] = next;
+      i += 1;
+    }
+  }
+  return out;
+}
+
+function mapConfig(kind) {
+  if (kind === "full") return MAP_CONFIG;
+  return {
+    ...MAP_CONFIG,
+    mapSize: { x: 48, y: 40 },
+    minCapitalLandmass: 8,
+    minCapitalDistance: 4,
+    citiesPerCiv: 4,
+    citySpacing: 3,
+    minContinents: 2,
+    smallIslandCount: 2,
+  };
+}
+
+// A representative national grid: one coal plant per city, one steel mill, one
+// chip foundry and a gold mine, all dropped on free land so the steady state
+// can be read without waiting for construction.
+function seedInfrastructure(state) {
+  for (let civ = 0; civ < state.civilisations.length; civ++) {
+    const plan = [
+      "coal_power_plant",
+      "coal_power_plant",
+      "coal_power_plant",
+      "coal_power_plant",
+      "coal_power_plant",
+      "steel_mill",
+      "chip_foundry",
+      "gold_mine",
+    ];
+    const tiles = (state._territoryByCiv.get(civ) || []).filter(
+      (coords) => state._isLand(coords) && !state.cityAt(coords)
+    );
+    let used = 0;
+    for (const id of plan) {
+      if (used >= tiles.length) break;
+      const coords = tiles[used++];
+      const k = key(coords.x, coords.y);
+      state.tileImprovements.set(k, id);
+      state.tileImprovementOwner.set(k, civ);
+      state.tileImprovementHp.set(k, 1000);
+      state._ensureResourceStock(k);
+    }
+  }
+}
+
+// A mature nation: every city carries a believable basket of buildings, so the
+// material upkeep (and repair bill) can be read.
+function seedBuildings(state) {
+  const basket = {
+    market: 3, bank: 2, barracks: 2, shelters: 1, aa_building: 1,
+    research_lab: 2, university: 1, museum: 1, cinema_studio: 1, airport: 1,
+  };
+  for (const city of state.cities) {
+    for (const [id, level] of Object.entries(basket)) {
+      const index = state.protoBuildings.findIndex((b) => b.id === id);
+      if (index < 0) continue;
+      if (state.protoBuildings[index].coastal && !state.isCoastalCity(city)) continue;
+      city.buildings[index] = level;
+    }
+  }
+  state._gdpPerCapitaCache.clear();
+  state._touchModifiers();
+}
+
+function eur(value) {
+  const abs = Math.abs(value);
+  if (abs >= 1e9) return `${(value / 1e9).toFixed(2)}B`;
+  if (abs >= 1e6) return `${(value / 1e6).toFixed(2)}M`;
+  if (abs >= 1e3) return `${(value / 1e3).toFixed(1)}k`;
+  return value.toFixed(0);
+}
+
+function num(value) {
+  const abs = Math.abs(value);
+  if (abs >= 1e9) return `${(value / 1e9).toFixed(2)}e9`;
+  if (abs >= 1e6) return `${(value / 1e6).toFixed(2)}e6`;
+  if (abs >= 1e3) return `${(value / 1e3).toFixed(1)}e3`;
+  return value.toFixed(1);
+}
+
+function pad(text, width, right = false) {
+  const value = String(text);
+  return right ? value.padStart(width) : value.padEnd(width);
+}
+
+console.log(`\n=== Resource production costs (base market prices, ${DAYS} days) ===`);
+console.log(
+  pad("building", 26) + pad("out/day", 12, true) + pad("energy/day", 13, true) +
+  pad("energy €/d", 11, true) + pad("upkeep €/d", 11, true) + pad("gross €/d", 11, true) +
+  pad("net €/d", 11, true) + pad("payback d", 10, true)
+);
+for (const building of RESOURCE_BUILDINGS) {
+  const energyPrice = RESOURCE_MARKET_BASE.energy;
+  const outputValue = building.resource === "energy"
+    ? building.outputPerDay * RESOURCE_MARKET_BASE.energy
+    : building.outputPerDay * (RESOURCE_MARKET_BASE[building.resource] || 0);
+  const energyCost = (building.energyPerDay || 0) * energyPrice;
+  const upkeep = building.maintenance * 24;
+  const net = outputValue - energyCost - upkeep;
+  const payback = net > 0 ? building.buildCost / net : Infinity;
+  console.log(
+    pad(building.id, 26) + pad(num(building.outputPerDay), 12, true) +
+    pad(num(building.energyPerDay || 0), 13, true) + pad(eur(energyCost), 11, true) +
+    pad(eur(upkeep), 11, true) + pad(eur(outputValue), 11, true) +
+    pad(eur(net), 11, true) + pad(Number.isFinite(payback) ? payback.toFixed(0) : "never", 10, true)
+  );
+}
+
+console.log(`\n=== Settled economy after ${DAYS} days (scenario: ${SCENARIO}, map: ${MAP}) ===`);
+for (let civ = 0; civ < civs.length; civ++) {
+  const population = state.getPlayerPopulation(civ);
+  const gdp = state.getPlayerGdp(civ);
+  const income = state.getCivHourlyIncome(civ) * 24;
+  const moneyUpkeep = state.getPlayerUpkeep(civ) * 24;
+  const upkeepDemand = state.getCivUpkeepResources(civ);
+  const spend = spendTotals[civ];
+  let energyNeed = 0;
+  let energySupply = 0;
+  for (const city of state.cities) {
+    if (city.civ !== civ) continue;
+    energyNeed += cityEnergyPerDay(state.getCityEconomy(city).gdp);
+  }
+  for (const [k, id] of state.tileImprovements) {
+    if (state.tileImprovementOwner.get(k) !== civ) continue;
+    const proto = RESOURCE_BUILDINGS.find((b) => b.id === id);
+    if (proto && proto.resource === "energy") energySupply += proto.outputPerDay;
+  }
+  const stock = state.getCivResourceSummary(civ);
+  console.log(
+    `\n-- ${civs[civ].name} --`
+  );
+  console.log(
+    `pop ${num(population)}  gdp ${eur(gdp)}  gdp/cap ${eur(population ? gdp / population : 0)}` +
+    `  budget ${eur(state.getBudget(civ))} (start ${eur(startBudget[civ])})`
+  );
+  console.log(
+    `income/d ${eur(income)}  campaign upkeep/d ${eur(moneyUpkeep)}  net/d ${eur(income - moneyUpkeep)}`
+  );
+  console.log(
+    `material upkeep/d: steel ${num(upkeepDemand.steel)} t  energy ${num(upkeepDemand.energy)} kWh` +
+    `  high-tech ${num(upkeepDemand.hightech)} u`
+  );
+  console.log(
+    `resource spend over run: energy ${eur(spend.energy)}  goods ${eur(spend.goods)}` +
+    `  transport ${eur(spend.transport)}  construction ${eur(spend.construction)}` +
+    `  upkeep ${eur(spend.upkeep)}  combat ${eur(spend.combat)}`
+  );
+  console.log(
+    `energy need/d ${num(energyNeed)} kWh  own supply/d ${num(energySupply)} kWh` +
+    `  bought-ish/d ${num((spend.energy / Math.max(DAYS, 1)) / Math.max(state.getResourcePrice("energy"), 1e-9))} kWh`
+  );
+  for (const id of ["food", "steel", "luxury", "hightech"]) {
+    console.log(
+      `  ${pad(id, 9)} stock ${num(stock.stock[id])}  need/d ${num(stock.need[id] || 0)}` +
+      `  produced/d ${num(stock.production[id] || 0)}`
+    );
+  }
+  let shortage = 0;
+  for (const city of state.cities) {
+    if (city.civ !== civ) continue;
+    const info = state.getCityResourceInfo(city);
+    for (const value of Object.values(info.shortage)) shortage += value;
+  }
+  console.log(`  summed city shortage fraction: ${shortage.toFixed(3)}`);
+}
+
+console.log("\n=== Market prices at the end ===");
+for (const id of Object.keys(RESOURCE_MARKET_BASE)) {
+  const stats = state.resourceMarketStats.get(id) || {};
+  console.log(
+    `  ${pad(id, 9)} price ${state.getResourcePrice(id).toFixed(4)}` +
+    ` (base ${RESOURCE_MARKET_BASE[id]})  supply ${num(stats.supply || 0)}  demand ${num(stats.demand || 0)}`
+  );
+}
+console.log(`\nRules: food ${RESOURCE_RULES.foodPerPersonPerDay} t/pp/d, steel ${RESOURCE_RULES.steelPerPersonPerDay} t/pp/d, luxury ${RESOURCE_RULES.luxuryPerPersonPerDay} ct/pp/d`);
+console.log(`energy intensity ${RESOURCE_RULES.gdpEnergyIntensity} kWh/€/yr, steel ${RESOURCE_RULES.energyPerSteelTonne / 1e6} GWh/t, food ${RESOURCE_RULES.energyPerFoodTonne / 1e6} GWh/t\n`);
@@ -21,6 +21,7 @@ const DELTA_COLLECTIONS = [
  "tileEthnicity",
  "cityStats",
  "visible",
+  "resourceGraph",
 ];

 // A wire move order carrying more units than this is split into chunks that
@@ -216,6 +217,8 @@ export class GameServer extends EventEmitter {
        return this._handlePolicy(civ, order);
      case "revoke_policy":
        return this._handleRevokePolicy(civ, order);
+      case "set_interest_rate":
+        return this.state.requestSetInterestRate(civ, Number(order.rate));
      default:
        return false;
    }
@@ -2,7 +2,7 @@
 // with the level, with no level cap; upkeep is 1% of that cost, so it follows
 // the level too.

-import { EFFECT_GDP, EFFECT_BUDGET_INCOME, EFFECT_RESEARCH, EFFECT_CULTURE, effect } from "./effects.js";
+import { EFFECT_PRODUCTION, EFFECT_BUDGET_INCOME, EFFECT_RESEARCH, EFFECT_CULTURE, effect } from "./effects.js";

 // Buildings whose benefit is a rule rather than a stat effect. Kept as ids so
 // the simulation and the UI can name them without magic strings.
@@ -15,8 +15,8 @@ export const BUILDING_MECHANIC = {
  CIVILIAN_SHELTER: "civilian_shelter",
  // Fires one volley at hostile aircraft passing over the city.
  AIR_DEFENSE: "air_defense",
-  // Flat GDP per capita for the city's region, per adjacent sea tile.
-  PORT_GDP: "port_gdp",
+  // Flat production per head for the city's region, per adjacent sea tile.
+  PORT_PRODUCTION: "port_production",
  // Lets people fly in from any other city with an airport.
  AIR_IMMIGRATION: "air_immigration",
 };
@@ -25,11 +25,11 @@ export const BUILDINGS = [
  {
    id: "market",
    name: "Market",
-    description: "A hub of local trade. Raises the GDP per capita of the city's region, with diminishing returns.",
+    description: "A hub of local trade. Raises the production of the city's region, with diminishing returns.",
    baseCost: 500_000,
    costAlpha: 1.2,
    refundFraction: 0.5,
-    effects: [effect(EFFECT_GDP, 0.04, 0.75)],
+    effects: [effect(EFFECT_PRODUCTION, 0.04, 0.75)],
    icon: "icon_market.svg",
  },
  {
@@ -70,6 +70,7 @@ export const BUILDINGS = [
  },
  {
    id: "aa_building",
+    advanced: true,
    name: "Air defense",
    description: "Damages hostile aircraft that fly above this city.",
    baseCost: 1_000_000_000,
@@ -77,10 +78,14 @@ export const BUILDINGS = [
    refundFraction: 0.5,
    effects: [],
    mechanic: "air_defense",
+    // Cheap to keep ready; the cost is in the ammunition it fires (see the
+    // combat consumption rules).
+    materialUpkeep: { steel: 0.5, energy: 500, hightech: 0 },
    icon: "icon_aa_building.svg",
  },
  {
    id: "research_lab",
+    advanced: true,
    name: "Research lab",
    description: "Applies science to industry and government. Produces research points for the whole nation.",
    baseCost: 100_000_000,
@@ -91,6 +96,7 @@ export const BUILDINGS = [
  },
  {
    id: "university",
+    advanced: true,
    name: "University",
    description: "Higher education produces research and a little culture for the whole nation.",
    baseCost: 100_000_000,
@@ -122,26 +128,30 @@ export const BUILDINGS = [
  {
    id: "port",
    name: "Port",
-    description: "Warm water port. Gains 1000 GDP/capita per tile per level.",
+    description: "Warm water port. Adds 1000 production per person per adjacent sea tile per level, and brings in extra food.",
    baseCost: 20_000_000,
    costAlpha: 1.7,
    refundFraction: 0.5,
    effects: [effect(EFFECT_BUDGET_INCOME, 0.08, 0.7)],
-    // Every tile the city's region covers gains this much GDP per capita for
-    // each sea tile next to the city, per port level.
-    mechanic: "port_gdp",
-    gdpPerCapitaPerSeaTilePerLevel: 1000,
+    // Every person in the city's region produces this much more, for each sea
+    // tile next to the city, per port level.
+    mechanic: "port_production",
+    productionPerSeaTilePerLevel: 1000,
+    // The region also grows this much more food, as a fraction of its output,
+    // for each sea tile beside the city, per port level.
+    foodPerSeaTilePerLevel: 0.05,
    icon: "icon_port.svg",
    coastal: true,
  },
  {
    id: "airport",
+    advanced: true,
    name: "Airport",
    description: "An airfield with a control tower. Lets the city train aircraft and serves as a home airbase for them to land and refuel. Immigration can reach this city from any other city in the world with an airport. The effect scales with airport level.",
    baseCost: 250_000_000,
    costAlpha: 1.7,
    refundFraction: 0.5,
-    effects: [effect(EFFECT_GDP, 0.05, 0.8)],
+    effects: [effect(EFFECT_PRODUCTION, 0.05, 0.8)],
    mechanic: "air_immigration",
    icon: "icon_airport.svg",
  },
@@ -1,11 +1,12 @@
-// The playable civilisations: colours, flag art and the pool of city names
-// drawn on when settlements are placed.
+// The playable civilisations: colours, flag art, national currency and the pool
+// of city names drawn on when settlements are placed.

 export const CIVILISATIONS = [
  {
    id: "france",
    name: "France",
    demonym: "French",
+    currency: { code: "FRF", symbol: "₣", name: "French Franc" },
    primaryColour: "#0d0d5c",
    accentColour: "#8c8c82",
    flag: "flag_france.png",
@@ -15,6 +16,7 @@ export const CIVILISATIONS = [
    id: "britain",
    name: "Britain",
    demonym: "British",
+    currency: { code: "GBP", symbol: "£", name: "British Pound" },
    primaryColour: "#a81818",
    accentColour: "#0722ff",
    flag: "flag_britain.png",
@@ -24,6 +26,7 @@ export const CIVILISATIONS = [
    id: "slovenia",
    name: "Slovenia",
    demonym: "Slovenian",
+    currency: { code: "SIT", symbol: "SIT", name: "Slovenian Tolar" },
    primaryColour: "#005da4",
    accentColour: "#ed1c24",
    flag: "flag_slovenia.png",
@@ -33,6 +36,7 @@ export const CIVILISATIONS = [
    id: "poland",
    name: "Poland",
    demonym: "Polish",
+    currency: { code: "PLN", symbol: "zł", name: "Polish Złoty" },
    primaryColour: "#a6000b",
    accentColour: "#ffffff",
    flag: "flag_poland.png",
@@ -42,6 +46,7 @@ export const CIVILISATIONS = [
    id: "switzerland",
    name: "Switzerland",
    demonym: "Swiss",
+    currency: { code: "CHF", symbol: "₣", name: "Swiss Franc" },
    primaryColour: "#da291c",
    accentColour: "#ffffff",
    flag: "flag_switzerland.png",
@@ -51,6 +56,7 @@ export const CIVILISATIONS = [
    id: "ticino",
    name: "Ticino",
    demonym: "Ticinese",
+    currency: { code: "TIF", symbol: "₣", name: "Ticinese Franc" },
    primaryColour: "#4646e0",
    accentColour: "#a6000b",
    flag: "flag_ticino.png",
@@ -60,6 +66,7 @@ export const CIVILISATIONS = [
    id: "galicia",
    name: "Galicia",
    demonym: "Galician",
+    currency: { code: "GAP", symbol: "₧", name: "Galician Peseta" },
    primaryColour: "#006dad",
    accentColour: "#ffffff",
    flag: "flag_galicia.png",
@@ -69,6 +76,7 @@ export const CIVILISATIONS = [
    id: "germany",
    name: "Germany",
    demonym: "German",
+    currency: { code: "DEM", symbol: "DM", name: "German Mark" },
    primaryColour: "#141414",
    accentColour: "#ffce00",
    flag: "flag_germany.png",
@@ -78,6 +86,7 @@ export const CIVILISATIONS = [
    id: "iran",
    name: "Iran",
    demonym: "Iranian",
+    currency: { code: "IRR", symbol: "﷼", name: "Iranian Rial" },
    primaryColour: "#18a645",
    accentColour: "#f01c21",
    flag: "flag_iran.png",
@@ -87,6 +96,7 @@ export const CIVILISATIONS = [
    id: "usa",
    name: "United States",
    demonym: "American",
+    currency: { code: "USD", symbol: "$", name: "US Dollar" },
    primaryColour: "#3c3b6e",
    accentColour: "#b22234",
    flag: "flag_usa.png",
@@ -97,6 +107,7 @@ export const CIVILISATIONS = [
    name: "Aotearoa",
    demonym: "New Zealander",
    adjective: "New Zealand",
+    currency: { code: "NZD", symbol: "$", name: "New Zealand Dollar" },
    primaryColour: "#00247d",
    accentColour: "#cc142b",
    flag: "flag_aotearoa.png",
@@ -107,6 +118,7 @@ export const CIVILISATIONS = [
    name: "New Hampshire",
    demonym: "New Hampshirite",
    adjective: "New Hampshire",
+    currency: { code: "NHD", symbol: "$", name: "New Hampshire Dollar" },
    primaryColour: "#12355b",
    accentColour: "#f2b705",
    flag: "flag_new_hampshire.png",
@@ -116,6 +128,7 @@ export const CIVILISATIONS = [
    id: "florida",
    name: "Florida",
    demonym: "Floridian",
+    currency: { code: "FLD", symbol: "$", name: "Floridian Dollar" },
    primaryColour: "#782f40",
    accentColour: "#ceb888",
    flag: "flag_florida.png",
@@ -125,6 +138,7 @@ export const CIVILISATIONS = [
    id: "australia",
    name: "Australia",
    demonym: "Australian",
+    currency: { code: "AUD", symbol: "$", name: "Australian Dollar" },
    primaryColour: "#00843d",
    accentColour: "#ffcd00",
    flag: "flag_australia.png",
@@ -134,6 +148,7 @@ export const CIVILISATIONS = [
    id: "uruguay",
    name: "Uruguay",
    demonym: "Uruguayan",
+    currency: { code: "UYU", symbol: "$U", name: "Uruguayan Peso" },
    primaryColour: "#0038a8",
    accentColour: "#fcd116",
    flag: "flag_uruguay.png",
@@ -143,6 +158,7 @@ export const CIVILISATIONS = [
    id: "vietnam",
    name: "Vietnam",
    demonym: "Vietnamese",
+    currency: { code: "VND", symbol: "₫", name: "Vietnamese Đồng" },
    primaryColour: "#da251d",
    accentColour: "#ffff00",
    flag: "flag_vietnam.png",
@@ -152,6 +168,7 @@ export const CIVILISATIONS = [
    id: "texas",
    name: "Texas",
    demonym: "Texan",
+    currency: { code: "TXD", symbol: "$", name: "Texan Dollar" },
    primaryColour: "#bf0a30",
    accentColour: "#002868",
    flag: "flag_texas.png",
@@ -161,6 +178,7 @@ export const CIVILISATIONS = [
    id: "alabama",
    name: "Alabama",
    demonym: "Alabamian",
+    currency: { code: "ALD", symbol: "$", name: "Alabaman Dollar" },
    primaryColour: "#9e1b32",
    accentColour: "#ffffff",
    flag: "flag_alabama.png",
@@ -7,11 +7,11 @@ export const CITY_GARRISON_HEAL_PER_HOUR = 1;
 // Combat is fought on a single tile: the attacking stack charges onto the
 // defending stack's tile and the two share it until one side is wiped out.
 // Every day a battle lasts the tile loses this fraction of its population and
-// of its GDP per capita. Once the fighting stops, GDP per capita recovers by
+// of its production per head. Once the fighting stops, production recovers by
 // `recoveryPerDay` each day, starting `recoveryDelayDays` after the last battle.
 export const BATTLE = {
  populationLossPerDay: 0.3,
-  gdpPerCapitaLossPerDay: 0.3,
+  productionLossPerDay: 0.3,
  recoveryDelayDays: 30,
  recoveryPerDay: 100,
  // Structures on a battlefield take this much damage each day of fighting.
@@ -19,19 +19,19 @@ export const BATTLE = {
 };

 // Pillaging: each unit removes this fraction of the tile's remaining
-// population, cuts its GDP per capita by this multiplier, and heals one hit
-// point per this many people driven off.
+// population, cuts its production per head by this multiplier, and heals one
+// hit point per this many people driven off.
 export const PILLAGE = {
  populationLoss: 0.1,
-  gdpPenalty: 0.7,
+  productionPenalty: 0.7,
  healPerPeople: 1000,
 };

 // Trenches: infantry dug into a tile are much harder to dislodge, at the cost
-// of the local economy. The defense figures are multipliers on a unit's base
+// of the local production. The defense figures are multipliers on a unit's base
 // defense; melee attackers get no bonus, artillery is heavily blunted.
 export const TRENCH = {
-  gdpMultiplier: 0.8,
+  productionMultiplier: 0.8,
  meleeDefenseMultiplier: 2.0,
  artilleryDefenseMultiplier: 3.0,
 };
@@ -71,7 +71,7 @@ export const AIR_DEFENSE = {

 // The result of pillaging a tile with `count` units in sequence, starting from
 // its current population. Each step removes a tenth of what is left and heals
-// for the people it removed; the GDP-per-capita multiplier compounds. Shared so
+// for the people it removed; the production multiplier compounds. Shared so
 // the server and the forecast tooltip compute the same numbers.
 export function pillageSteps(population, count) {
  const steps = [];
@@ -81,5 +81,5 @@ export function pillageSteps(population, count) {
    remaining -= removed;
    steps.push({ removed, remaining, heal: removed / PILLAGE.healPerPeople });
  }
-  return { steps, gdpMultiplier: Math.pow(PILLAGE.gdpPenalty, count) };
+  return { steps, productionMultiplier: Math.pow(PILLAGE.productionPenalty, count) };
 }
@@ -8,12 +8,55 @@ import { HOURS_PER_YEAR } from "../game_clock.js";
 // rate below is what the per-tick economy actually uses.
 export const ANNUAL_TAX_RATE = 0.25;

+// The buckets the monthly budget report groups a nation's spending into. Each
+// row carries a signed cash movement (positive is money into the treasury) and,
+// for the upkeep rows, the market value of the materials consumed whether they
+// were drawn from stores or bought. `group` is the heading the table files the
+// row under.
+export const BUDGET_EXPENSE_CATEGORIES = [
+  { id: "buildings", label: "Building upkeep", group: "Upkeep" },
+  { id: "units", label: "Unit upkeep", group: "Upkeep" },
+  { id: "works", label: "Tile works", group: "Upkeep" },
+  { id: "transport", label: "Transport", group: "Upkeep" },
+  { id: "campaign", label: "Campaign", group: "Government" },
+  { id: "construction", label: "Construction", group: "Investment" },
+  { id: "training", label: "Training", group: "Investment" },
+  { id: "tilebuild", label: "Tile improvements", group: "Investment" },
+  { id: "provisioning", label: "Provisioning", group: "Resources" },
+  { id: "energy", label: "Power", group: "Resources" },
+  { id: "military", label: "Military supplies", group: "Resources" },
+];
+
+// The monetary system: each nation issues its own currency and runs a central
+// bank. Regions are the private sector, each holding a basket of currencies.
+// When their cash runs out they borrow from the central bank, and the same bank
+// lets the government run an overdraft. The interest rate is the cost of that
+// borrowing, not a direct lever on inflation.
+export const MONEY = {
+  // The central bank's opening lending rate, charged on every debt each year,
+  // and the ceiling a player may set.
+  defaultInterestRate: 0.02,
+  maxInterestRate: 0.5,
+  // Private-sector cash a region opens with, as a share of its yearly GDP.
+  privateCashFraction: 0.5,
+  // Each day a region converts this share of every foreign holding back into its
+  // own currency.
+  repatriationPerDay: 0.05,
+  // How much a currency's value may move from par, either way.
+  maxRateDrift: 0.9,
+  // How hard a day's net foreign demand pushes a currency's value.
+  demandSensitivity: 0.5,
+  // When several regions chase the same scarce surplus, each further buyer
+  // raises the price it pays by this share, capped at `maxBidMultiplier`.
+  bidPremium: 0.3,
+  maxBidMultiplier: 2,
+};
+
 export const ECONOMY = {
-  baseGdpPerCapita: 10_000,
  basePopulation: 100_000,
-  cityTileGdpMultiplier: 2.0,
-  capitalTileGdpMultiplier: 2.5,
-  citySurroundingGdpBonus: 0.3,
+  cityTileProductionMultiplier: 2.0,
+  capitalTileProductionMultiplier: 2.5,
+  citySurroundingProductionBonus: 0.3,
  gdpPerProductionPoint: 100_000,
  // 25% of GDP per year, spread evenly over the hours of the year.
  taxRatePerYear: ANNUAL_TAX_RATE,
@@ -22,10 +65,10 @@ export const ECONOMY = {
  startingBudgetFraction: 0.1,
  startingBudget: 1_000_000_000,
  basePopulationGrowthRate: 0.005,
-  // Natural growth of GDP per capita: every day a tile gains this share of the
-  // GDP per capita it opened the game with. The amount is constant, so the
-  // relative growth rate naturally tapers off as the years pass.
-  naturalGdpGrowthPerDay: 0.0001,
+  // Natural growth of production: every day a tile gains this share of the
+  // production it opened the game with. The amount is constant, so the relative
+  // growth rate naturally tapers off as the years pass.
+  naturalProductionGrowthPerDay: 0.0001,

  productionCapacity(gdp) {
    if (this.gdpPerProductionPoint <= 0) return 0;
@@ -2,7 +2,8 @@
 // technologies). An effect scales with a level so a building's benefit grows
 // with each upgrade.

-export const EFFECT_GDP = "gdp";
+// Every stat that modifies a tile's or a nation's production, in display order.
+export const EFFECT_PRODUCTION = "production";
 export const EFFECT_RESEARCH = "research";
 export const EFFECT_CULTURE = "culture";
 export const EFFECT_BUDGET_INCOME = "budget_income";
@@ -1,7 +1,7 @@
 // Forms of government a civilisation may adopt. Each grants a flat modifier to
 // the stats it favours.

-import { EFFECT_GDP, EFFECT_BUDGET_INCOME, EFFECT_RESEARCH, EFFECT_CULTURE, effect } from "./effects.js";
+import { EFFECT_PRODUCTION, EFFECT_BUDGET_INCOME, EFFECT_RESEARCH, EFFECT_CULTURE, effect } from "./effects.js";

 export const GOVERNMENTS = [
  {
@@ -10,7 +10,7 @@ export const GOVERNMENTS = [
    description: "Rule by elected representatives. A balanced government that spreads its support across the economy, the treasury and the sciences.",
    baseCost: 0,
    costGdpFraction: 0.02,
-    effects: [effect(EFFECT_GDP, 0.05, 1.0), effect(EFFECT_BUDGET_INCOME, 0.1, 1.0), effect(EFFECT_RESEARCH, 1.0, 1.0)],
+    effects: [effect(EFFECT_PRODUCTION, 0.05, 1.0), effect(EFFECT_BUDGET_INCOME, 0.1, 1.0), effect(EFFECT_RESEARCH, 1.0, 1.0)],
  },
  {
    id: "monarchy",
@@ -18,7 +18,7 @@ export const GOVERNMENTS = [
    description: "Rule by a hereditary sovereign. The crown favours commerce and tradition, lifting the economy and the nation's cultural output.",
    baseCost: 0,
    costGdpFraction: 0.03,
-    effects: [effect(EFFECT_GDP, 0.1, 1.0), effect(EFFECT_CULTURE, 1.0, 1.0)],
+    effects: [effect(EFFECT_PRODUCTION, 0.1, 1.0), effect(EFFECT_CULTURE, 1.0, 1.0)],
  },
  {
    id: "technocracy",
@@ -26,7 +26,7 @@ export const GOVERNMENTS = [
    description: "Rule by technical experts. A single-minded drive for progress pours resources into research while economic growth takes second place.",
    baseCost: 0,
    costGdpFraction: 0.04,
-    effects: [effect(EFFECT_RESEARCH, 3.0, 1.0), effect(EFFECT_GDP, 0.03, 1.0)],
+    effects: [effect(EFFECT_RESEARCH, 3.0, 1.0), effect(EFFECT_PRODUCTION, 0.03, 1.0)],
  },
 ];

@@ -3,6 +3,8 @@
 // again as a road. Both are bought outright and then cost an hourly maintenance
 // for every tile of the network a nation holds.

+import { resourceBuildingById } from "./resources.js";
+
 export const TRANSPORT_IMPROVEMENTS = [
  {
    id: "road",
@@ -57,6 +59,7 @@ export const TILE_IMPROVEMENTS = [
  },
  {
    id: "radar_tower",
+    advanced: true,
    name: "Radar tower",
    description:
      "Watches five tiles out. A ranged hit damages it and an enemy walking onto it captures it.",
@@ -69,6 +72,7 @@ export const TILE_IMPROVEMENTS = [
  },
  {
    id: "coastal_cannon",
+    advanced: true,
    name: "Coastal cannon",
    description:
      "Automatically fires on hostile warships within two tiles. Only a coastal tile can carry one.",
@@ -86,6 +90,13 @@ export const TILE_IMPROVEMENT_BY_ID = Object.fromEntries(
  TILE_IMPROVEMENTS.map((improvement) => [improvement.id, improvement])
 );

+// A tile-owned building is either a military improvement or a resource
+// producer. Both share the tile-improvement maps, the tile-works construction
+// queue and the hourly upkeep, so the lookup folds the two catalogues together.
 export function tileImprovementById(id) {
-  return TILE_IMPROVEMENT_BY_ID[id] || null;
+  return TILE_IMPROVEMENT_BY_ID[id] || resourceBuildingById(id) || null;
+}
+
+export function isResourceTileBuilding(proto) {
+  return !!(proto && proto.resource && proto.outputPerDay !== undefined);
 }
@@ -16,4 +16,5 @@ export * from "./politics.js";
 export * from "./map_config.js";
 export * from "./terrain.js";
 export * from "./roads.js";
+export * from "./resources.js";
 export * from "./improvements.js";
@@ -160,6 +160,38 @@ export const MIGRATION = {
  airportSharePerDay: 0.0005,
  // The approval at or above which nobody is inclined to leave.
  comfortableApproval: 0.9,
+
+  // People move only to a region at least this much richer per head, and the
+  // bar rises with the travel time: a destination `time` hours away must be
+  // `incomeRatioBase * (1 + time * incomeTimePenalty)` times as rich. So the
+  // closer and richer a place is, the more attractive.
+  incomeRatioBase: 2,
+  incomeTimePenalty: 0.02,
+  // People travel the transport network; a tile of open terrain costs this many
+  // hours at walking pace, a road or railway less, open water a flat sea rate.
+  peopleSpeed: 1,
+  seaHoursPerTile: 1.5,
+  // Land routes are only traced this far; beyond it a destination is reachable
+  // only by air.
+  maxTravelHours: 120,
+  // Of the people who qualify, this share of the poorer region moves per day,
+  // scaled by how far the ratio clears the bar and capped.
+  incomeSharePerDay: 0.0015,
+  incomeGapCap: 1,
+  // No single day moves more than this share of a region's people by land.
+  incomeMaxSharePerDay: 0.005,
+  // An airport flies people over the distance at a flat time cost, but moves at
+  // most this many people per day for each airport level on the route.
+  airHours: 6,
+  airPeoplePerDayPerLevel: 1000,
+
+  // At generation, regions of a nation trade people until their production per
+  // head is level. `equalizeTolerance` is the residual spread accepted and
+  // `equalizePasses` bounds the refinement; no region is emptied below
+  // `minRegionPopulation`.
+  equalizeTolerance: 0.005,
+  equalizePasses: 30,
+  minRegionPopulation: 20000,
 };

 // A pillaged tile is a war crime. The people of the tile loathe the aggressor
@@ -0,0 +1,414 @@
+// Resources: the five material groups nations produce, store, trade and
+// consume. Everything is expressed in one canonical unit per resource so the
+// simulation never has to convert: energy in kWh, steel and food in tonnes,
+// luxury in carats and high-tech in whole units. Display formatting converts to
+// the friendly unit (MWh, Mt, kt, ...). The market prices and conversion ratios
+// here are the main tuning knobs for the whole resource economy; the per-person
+// needs and the energy-per-material figures come straight from the roadmap.
+
+// Energy is stored and moved as kWh. These keep the catalogue readable.
+export const KWH_PER_MWH = 1_000;
+export const KWH_PER_GWH = 1_000_000;
+export const KWH_PER_TWH = 1_000_000_000;
+
+// One tonne of any material counts as this much energy on the wire, so material
+// deliveries and energy deliveries share one transport-cost formula.
+export const ENERGY_PER_MATERIAL_TONNE = 10 * KWH_PER_GWH; // 10 GWh/t
+
+export const RESOURCES = [
+  {
+    id: "energy",
+    name: "Energy",
+    unit: "kWh",
+    icon: "icon_electricity.svg",
+    colour: "#ffd633",
+    // Mass of one canonical unit, so a delivery leg can charge transport per
+    // tonne whatever the good is: 10 GWh of energy weighs a tonne.
+    tonnesPerUnit: 1 / ENERGY_PER_MATERIAL_TONNE,
+    // Energy is a flow, not a stock: it comes from the grid and is spent the
+    // same day. Only cities and resource buildings can hold the other four.
+    storable: false,
+  },
+  {
+    id: "steel",
+    colour: "#9aa7b8",
+    name: "Steel",
+    unit: "t",
+    icon: "icon_steel.svg",
+    tonnesPerUnit: 1,
+    storable: true,
+  },
+  {
+    id: "food",
+    colour: "#7ed957",
+    name: "Food",
+    unit: "t",
+    icon: "icon_food.svg",
+    tonnesPerUnit: 1,
+    storable: true,
+  },
+  {
+    id: "luxury",
+    colour: "#d98cff",
+    name: "Luxury",
+    unit: "ct",
+    icon: "icon_luxury.svg",
+    // A carat is 0.2 g, so 200,000 ct weigh a tonne.
+    tonnesPerUnit: 0.0002 / 1000,
+    storable: true,
+  },
+  {
+    id: "hightech",
+    colour: "#5cc8ff",
+    name: "High-tech",
+    unit: "u",
+    icon: "icon_hightech.svg",
+    // A high-tech unit is a crate of components, about a kilogram.
+    tonnesPerUnit: 0.001,
+    storable: true,
+  },
+];
+
+export const RESOURCE_IDS = RESOURCES.map((r) => r.id);
+export const RESOURCE_INDEX = Object.fromEntries(RESOURCES.map((r, i) => [r.id, i]));
+// The four stockable resources, in catalogue order. Energy is handled as a flow.
+export const STORABLE_RESOURCE_IDS = RESOURCES.filter((r) => r.storable).map((r) => r.id);
+
+export function resourceById(id) {
+  return RESOURCES[RESOURCE_INDEX[id]] || null;
+}
+
+// Global market prices, in euro per canonical unit. These are what a city pays
+// when it cannot meet a need from its own store or a neighbour. Energy is
+// deliberately cheap: the roadmap's energy-per-material ratios are large, so a
+// high electric price would make every material's energy bill dwarf its value.
+//
+// The five figures are the old nominal prices raised roughly seventeen-fold so
+// the production-based GDP (what a nation makes times these prices) lands in
+// the same range as the money economy it replaced. The scaling is what makes a
+// fresh nation's food output alone read as a plausible per-capita GDP rather
+// than a few hundred euro; construction, upkeep and imports are priced off the
+// same figures.
+export const RESOURCE_MARKET_BASE = {
+  energy: 0.051, // per kWh
+  steel: 10_200, // per tonne
+  food: 5_100, // per tonne
+  luxury: 1_020, // per carat
+  hightech: 13_600, // per unit
+};
+
+// How strongly a day's world-wide imbalance moves the price, and how far it may
+// drift from the base. The market is a smoothing device, not a real auction:
+// it lets a shortage raise the cost of imports and a glut cheapen them.
+export const RESOURCE_MARKET = {
+  base: RESOURCE_MARKET_BASE,
+  adjustment: 0.2,
+  minMultiplier: 0.5,
+  maxMultiplier: 1.8,
+};
+
+// The physical rules of the resource economy. Every per-person figure and every
+// energy-per-material ratio below is fixed by the design; the prices above are
+// what we tune against them.
+export const RESOURCE_RULES = {
+  // Each person eats 1 kg of food and consumes 1 kg of steel a day. Both are
+  // canonical tonnes, so 1 kg is 0.001 t.
+  foodPerPersonPerDay: 0.001,
+  steelPerPersonPerDay: 0.001,
+  // Luxuries are rarer: 0.01 carat a person a day.
+  luxuryPerPersonPerDay: 0.01,
+  // Cities aim to hold 130% of a month's food before the month begins.
+  foodMonthlyBuffer: 1.3,
+  daysPerMonth: 30,
+
+  // A city's baseline electric appetite, in kWh per euro of yearly GDP. This is
+  // the "kWh per euro of GDP" economic metric; the top bar does not show it.
+  gdpEnergyIntensity: 0.15,
+
+  // Energy the material producers consume to make one canonical unit.
+  energyPerFoodTonne: 1 * KWH_PER_MWH, // 1 MWh per tonne
+  energyPerSteelTonne: 20 * KWH_PER_MWH, // 20 MWh per tonne
+  energyPerLuxuryCarat: {
+    gold_mine: 10 * KWH_PER_MWH, // 10 MWh per carat
+    diamond_mine: 5 * KWH_PER_MWH, // 5 MWh per carat
+  },
+  energyPerHighTechUnit: 100 * KWH_PER_MWH, // 100 MWh per unit
+  // Science buildings spend one high-tech unit for every research point.
+  highTechPerResearchPoint: 1,
+
+  // Delivering one tonne of material one tile, in kWh of transport energy.
+  // Roads use trucks, railways trains; without a road a truck burns the
+  // off-road figure times the tile's movement cost, and sea legs go by ship.
+  deliveryEnergy: {
+    truckRoad: 10 * KWH_PER_MWH, // 10 MWh per tonne per tile
+    truckOffRoad: 50 * KWH_PER_MWH, // 50 MWh per tonne per tile, times cost
+    train: 1 * KWH_PER_MWH, // 1 MWh per tonne per tile
+    ship: 50, // 50 kWh per tonne per tile
+  },
+
+  // Steel every construction spends per euro of its money cost. At 1/10000 a
+  // 100 M building needs 10,000 t of steel.
+  steelPerBudgetEuro: 1 / 10_000,
+  // The electricity a tile work draws as it is built, per euro of its money
+  // cost. It is roughly the power embodied in the steel it spends: steel costs
+  // 20 MWh a tonne and 1 t per 10,000 euro, so building is powered as well as
+  // supplied. Tile improvements pay this up front.
+  constructionEnergyPerBudgetEuro: 2, // kWh per euro
+  // High-tech a science or advanced building needs to be raised, per level.
+  constructionHighTechPerLevel: 100,
+
+  // Upkeep is materials, not money: every building, unit and improvement wears
+  // out and the state buys what it needs. Each figure scales with the thing's
+  // money value -- a building level's cost, a unit's training cost -- so one set
+  // of coefficients tunes the whole load. `advanced` things (science, air,
+  // radar, chips, fusion) also need high-tech.
+  upkeepSteelPerEuro: 5e-7, // t per euro of value per day
+  upkeepEnergyPerEuro: 1e-3, // kWh per euro of value per day
+  upkeepHighTechPerEuro: 2e-6, // u per euro of value per day (advanced only)
+
+  // Transport is the exception: its build cost is enormous but its upkeep is a
+  // per-tile wear figure, not a share of that cost.
+  transportUpkeepSteel: { road: 0.02, railway: 0.1 },
+
+  // Combat is the other exception: guns and aircraft are cheap to keep parked
+  // and expensive to fire. These are the materials one use spends. Air defense
+  // fires per hostile aircraft pass, artillery per hourly shelling, an aircraft
+  // per sortie.
+  combatConsumption: {
+    airDefenseVolley: { steel: 20, hightech: 5 },
+    artilleryVolley: { steel: 1, hightech: 0 },
+    airStrike: { steel: 100, hightech: 20 },
+  },
+
+  // Infantry eat. A unit carries this many soldiers, and each is fed like a
+  // civilian: double rations in combat, triple while wounded and resting.
+  // Training or healing a unit draws its soldiers out of the region's people.
+  unitPopulation: 1_000,
+  infantryCombatFoodMultiplier: 2,
+  infantryRestingFoodMultiplier: 3,
+
+  // Supply. A unit carries this many days of its own food. At home, or in
+  // foreign territory with a clear route to an allied city, it tops up from
+  // that city; cut off, the days run down and the unit starts to starve.
+  unitSupplyDays: 50,
+  starvationHpFractionPerDay: 0.1,
+
+  // Repairs: damage leaves a materials debt the owner pays down, and only then
+  // does the structure recover. A razed city level costs what it cost to build.
+  repair: {
+    steelPerTileHp: 0.05, // t to restore one hit point of a tile work
+    tileHpPerDay: 60, // hit points a funded repair restores each day
+    steelPerDamage: 0.5, // t of debt per point of structure damage
+    unitSteelPerHp: 0.01, // t to heal one hit point of a ground or naval unit
+    unitHighTechPerHp: 0.002, // u to heal one hit point of an advanced unit
+  },
+
+  // Fraction of a missing need that turns into a popularity penalty per day,
+  // and the same for a GDP-per-capita shortfall, so shortages are felt.
+  shortagePopularityPenalty: 2,
+  shortageGdpPenalty: 0.05,
+
+  // Food comes from the land, not from the number of people standing on it:
+  // every worked tile grows `foodPerTilePerDay` tonnes a day scaled by its
+  // terrain, so moving people between regions changes only income per head.
+  foodPerTilePerDay: 100,
+  // How fertile each terrain is. A worked tile grows its base output scaled by
+  // this, so forests and plains feed cities while deserts and ice do not.
+  tileFoodFactor: {
+    Forest: 1.4,
+    Hills: 0.7,
+    Land: 1.2,
+    Desert: 0.1,
+    Mountain: 0.2,
+    Tundra: 0.2,
+    Ice: 0,
+  },
+};
+
+// How far a city will look for a neighbour's surplus before falling back to the
+// global market.
+export const RESOURCE_TRADE_RADIUS = 8;
+
+// Resource-producing buildings. Built only outside cities, they occupy a land
+// tile like a military improvement and are managed through the same tile-works
+// queue. A power plant produces energy; every other building consumes energy
+// and produces its material. `outputPerDay` is in the resource's canonical
+// unit, `energyPerDay` in kWh (positive means consumed, negative produced).
+export const RESOURCE_BUILDINGS = [
+  {
+    id: "coal_power_plant",
+    name: "Coal power plant",
+    description:
+      "Burns coal to make 250 GWh of electricity a day. Cheap to raise, but the fuel bill never stops.",
+    resource: "energy",
+    outputPerDay: 250 * KWH_PER_GWH,
+    fuelEnergyPerDay: 250 * KWH_PER_GWH * 0.25,
+    energyPerDay: 0,
+    buildCost: 500_000_000,
+    maintenance: 20_000,
+    icon: "icon_coal_power_plant.svg",
+  },
+  {
+    id: "natural_gas_power_plant",
+    name: "Natural gas power plant",
+    description:
+      "The cleanest fossil plant: 300 GWh a day for a higher fuel bill.",
+    resource: "energy",
+    outputPerDay: 300 * KWH_PER_GWH,
+    fuelEnergyPerDay: 300 * KWH_PER_GWH * 0.25,
+    energyPerDay: 0,
+    buildCost: 700_000_000,
+    maintenance: 25_000,
+    icon: "icon_gas_power_plant.svg",
+  },
+  {
+    id: "oil_power_plant",
+    name: "Oil power plant",
+    description: "Burns oil for 270 GWh of electricity a day.",
+    resource: "energy",
+    outputPerDay: 270 * KWH_PER_GWH,
+    fuelEnergyPerDay: 270 * KWH_PER_GWH * 0.25,
+    energyPerDay: 0,
+    buildCost: 600_000_000,
+    maintenance: 22_000,
+    icon: "icon_oil_power_plant.svg",
+  },
+  {
+    id: "solar_power_plant",
+    name: "Solar power plant",
+    description:
+      "A field of panels producing a steady 30 GWh a day with no fuel and no upkeep.",
+    resource: "energy",
+    outputPerDay: 30 * KWH_PER_GWH,
+    energyPerDay: 0,
+    renewable: true,
+    buildCost: 300_000_000,
+    maintenance: 0,
+    icon: "icon_solar_power_plant.svg",
+  },
+  {
+    id: "geothermal_plant",
+    name: "Geothermal plant",
+    description: "Taps the earth's heat for 60 GWh a day of free electricity.",
+    resource: "energy",
+    outputPerDay: 60 * KWH_PER_GWH,
+    energyPerDay: 0,
+    renewable: true,
+    buildCost: 800_000_000,
+    maintenance: 0,
+    icon: "icon_geothermal_plant.svg",
+  },
+  {
+    id: "wind_turbines",
+    name: "Wind turbines",
+    description: "A hilltop wind farm making 25 GWh a day for free.",
+    resource: "energy",
+    outputPerDay: 25 * KWH_PER_GWH,
+    energyPerDay: 0,
+    renewable: true,
+    buildCost: 200_000_000,
+    maintenance: 0,
+    icon: "icon_wind_turbines.svg",
+  },
+  {
+    id: "offshore_wind_turbines",
+    name: "Offshore wind turbines",
+    description: "Turbines out at sea making 50 GWh a day. Needs a coastal tile.",
+    resource: "energy",
+    outputPerDay: 50 * KWH_PER_GWH,
+    energyPerDay: 0,
+    renewable: true,
+    coastal: true,
+    buildCost: 500_000_000,
+    maintenance: 0,
+    icon: "icon_offshore_wind_turbines.svg",
+  },
+  {
+    id: "fusion_power_plant",
+    advanced: true,
+    name: "Fusion power plant",
+    description: "A late-game reactor producing 4 TWh of electricity a day.",
+    resource: "energy",
+    outputPerDay: 4_000 * KWH_PER_GWH,
+    energyPerDay: 0,
+    renewable: true,
+    buildCost: 50_000_000_000,
+    maintenance: 50_000,
+    // A wonder of the endgame: only a nation that has mastered fusion may raise
+    // one. Its upkeep is deliberately high but not the raw share of its enormous
+    // build cost.
+    requiresTechnology: "fusion_power",
+    materialUpkeep: { steel: 1_000, energy: 0, hightech: 500 },
+    icon: "icon_fusion_power_plant.svg",
+  },
+  {
+    id: "steel_mill",
+    name: "Steel mill",
+    description:
+      "Smelts iron into 2000 t of steel a day, spending 20 MWh of energy per tonne.",
+    resource: "steel",
+    outputPerDay: 2_000,
+    energyPerDay: 2_000 * RESOURCE_RULES.energyPerSteelTonne,
+    buildCost: 800_000_000,
+    maintenance: 10_000,
+    icon: "icon_steel_mill.svg",
+  },
+  {
+    id: "gold_mine",
+    name: "Gold mine",
+    description: "Produces 20,000 carats of luxury a day, at 10 MWh a carat.",
+    resource: "luxury",
+    outputPerDay: 20_000,
+    energyPerDay: 20_000 * RESOURCE_RULES.energyPerLuxuryCarat.gold_mine,
+    buildCost: 400_000_000,
+    maintenance: 5_000,
+    icon: "icon_gold_mine.svg",
+  },
+  {
+    id: "diamond_mine",
+    name: "Diamond mine",
+    description: "Produces 20,000 carats of luxury a day, at 5 MWh a carat.",
+    resource: "luxury",
+    outputPerDay: 20_000,
+    energyPerDay: 20_000 * RESOURCE_RULES.energyPerLuxuryCarat.diamond_mine,
+    buildCost: 500_000_000,
+    maintenance: 5_000,
+    icon: "icon_diamond_mine.svg",
+  },
+  {
+    id: "chip_foundry",
+    advanced: true,
+    name: "Chip foundry",
+    description:
+      "Fabricates 5000 units of high-tech a day, spending 100 MWh of energy per unit.",
+    resource: "hightech",
+    outputPerDay: 5_000,
+    energyPerDay: 5_000 * RESOURCE_RULES.energyPerHighTechUnit,
+    buildCost: 2_000_000_000,
+    maintenance: 10_000,
+    icon: "icon_chip_foundry.svg",
+  },
+];
+
+// One work stands for a whole industry: its output is scaled up so a nation
+// needs far fewer of them on the map. The energy and fuel it draws scale with
+// the output too, so a converter stays exactly as efficient as it was authored.
+export const RESOURCE_BUILDING_OUTPUT_SCALE = 10;
+for (const building of RESOURCE_BUILDINGS) {
+  building.outputPerDay = (building.outputPerDay || 0) * RESOURCE_BUILDING_OUTPUT_SCALE;
+  building.energyPerDay = (building.energyPerDay || 0) * RESOURCE_BUILDING_OUTPUT_SCALE;
+  building.fuelEnergyPerDay = (building.fuelEnergyPerDay || 0) * RESOURCE_BUILDING_OUTPUT_SCALE;
+}
+
+// The resource buildings decay in battle like the military improvements do.
+for (const building of RESOURCE_BUILDINGS) {
+  if (building.takesCombatDamage === undefined) building.takesCombatDamage = true;
+}
+
+export const RESOURCE_BUILDING_BY_ID = Object.fromEntries(
+  RESOURCE_BUILDINGS.map((building) => [building.id, building])
+);
+
+export function resourceBuildingById(id) {
+  return RESOURCE_BUILDING_BY_ID[id] || null;
+}
@@ -8,7 +8,7 @@
 // news event (it only notifies the player).

 import {
-  EFFECT_GDP,
+  EFFECT_PRODUCTION,
  EFFECT_BUDGET_INCOME,
  EFFECT_RESEARCH,
  EFFECT_CULTURE,
@@ -36,17 +36,17 @@ export const TECHNOLOGIES = [
    theme: "science",
    cost: 20,
    prerequisites: [],
-    effects: [effect(EFFECT_RESEARCH, 1.0, 1.0), effect(EFFECT_GDP, 0.02, 1.0)],
+    effects: [effect(EFFECT_RESEARCH, 1.0, 1.0), effect(EFFECT_PRODUCTION, 0.02, 1.0)],
  },
  {
    id: "industrial_automation",
    name: "Industrial Automation",
-    description: "Robotics and control systems take over the factory floor, lifting national output.",
+    description: "Robotics and control systems take over the factory floor, lifting national production.",
    theme: "economy",
    repeatable: true,
    cost: 60,
    prerequisites: ["scientific_method"],
-    effects: [effect(EFFECT_GDP, 0.08, 1.0)],
+    effects: [effect(EFFECT_PRODUCTION, 0.08, 1.0)],
  },
  {
    id: "renewable_energy",
@@ -55,7 +55,7 @@ export const TECHNOLOGIES = [
    theme: "economy",
    cost: 80,
    prerequisites: ["scientific_method"],
-    effects: [effect(EFFECT_GDP, 0.03, 1.0), effect(EFFECT_BUDGET_INCOME, 0.05, 1.0)],
+    effects: [effect(EFFECT_PRODUCTION, 0.03, 1.0), effect(EFFECT_BUDGET_INCOME, 0.05, 1.0)],
  },
  {
    id: "quantum_computing",
@@ -73,7 +73,17 @@ export const TECHNOLOGIES = [
    theme: "science",
    cost: 300,
    prerequisites: ["industrial_automation", "quantum_computing"],
-    effects: [effect(EFFECT_CULTURE, 3.0, 1.0), effect(EFFECT_GDP, 0.05, 1.0)],
+    effects: [effect(EFFECT_CULTURE, 3.0, 1.0), effect(EFFECT_PRODUCTION, 0.05, 1.0)],
+  },
+  {
+    id: "fusion_power",
+    name: "Fusion Power",
+    description: "Controlled fusion. The key to the fusion power plant, and the most expensive research a nation can undertake.",
+    theme: "science",
+    // 500,000 research points, a lifetime's work for a mature nation.
+    cost: 5_000,
+    prerequisites: ["space_program", "quantum_computing"],
+    effects: [effect(EFFECT_RESEARCH, 8.0, 1.0)],
  },

  // Repeatable levels. Each raises a single stat by 1% of its base value.
@@ -138,11 +148,17 @@ export function technologyById(id) {
  return TECHNOLOGIES.find((t) => t.id === id) || null;
 }

+// Research is deliberately expensive: the catalogue lists the thematic base
+// price, and every effective cost is scaled by this factor. Keeping the scale
+// in one place lets the whole tree be retuned without touching each entry.
+export const RESEARCH_COST_MULTIPLIER = 100;
+
 // The cost of the next level of a technology given how many times it has been
 // researched already. Non-repeatable technologies cost the same either way.
 export function technologyCost(proto, repeatCount = 0) {
  if (!proto) return 0;
-  if (!proto.repeatable) return proto.cost;
+  const base = proto.cost * RESEARCH_COST_MULTIPLIER;
+  if (!proto.repeatable) return base;
  const growth = proto.repeatCostGrowth || 0;
-  return proto.cost * Math.pow(1 + growth, Math.max(0, repeatCount));
+  return base * Math.pow(1 + growth, Math.max(0, repeatCount));
 }
@@ -5,14 +5,14 @@
 // the fraction added to a unit's defense while it stands on the tile.

 export const TERRAIN_TILES = [
-  { col: 0, terrainType: "Forest", terrainClass: "Land", populationMultiplier: 0.3, gdpMultiplier: 0.5, movementCostMultiplier: 1.5, defenseBonus: 0.33, minElevation: 0.06 },
-  { col: 1, terrainType: "Hills", terrainClass: "Land", populationMultiplier: 0.7, gdpMultiplier: 0.8, movementCostMultiplier: 1.8, defenseBonus: 0.33, minElevation: 0.2 },
-  { col: 2, terrainType: "Ice", terrainClass: "Ice", populationMultiplier: 0, gdpMultiplier: 0, movementCostMultiplier: 4.0, defenseBonus: 0, minElevation: 0 },
-  { col: 3, terrainType: "Land", terrainClass: "Land", populationMultiplier: 1.0, gdpMultiplier: 1.0, movementCostMultiplier: 1.0, defenseBonus: 0, minElevation: -0.08 },
-  { col: 4, terrainType: "Desert", terrainClass: "Land", populationMultiplier: 0.05, gdpMultiplier: 0.2, movementCostMultiplier: 3.0, defenseBonus: 0, minElevation: -0.2 },
-  { col: 5, terrainType: "Sea", terrainClass: "Sea", populationMultiplier: 0, gdpMultiplier: 0, movementCostMultiplier: 0, defenseBonus: 0, minElevation: 0 },
-  { col: 6, terrainType: "Mountain", terrainClass: "Land", populationMultiplier: 0.1, gdpMultiplier: 0.8, movementCostMultiplier: 5.0, defenseBonus: 1.0, minElevation: 0.34 },
-  { col: 6, terrainType: "Tundra", terrainClass: "Land", populationMultiplier: 0.05, gdpMultiplier: 0.2, movementCostMultiplier: 2.0, defenseBonus: 0, minElevation: 0 },
+  { col: 0, terrainType: "Forest", terrainClass: "Land", populationMultiplier: 0.3, productionMultiplier: 0.5, movementCostMultiplier: 1.5, defenseBonus: 0.33, minElevation: 0.06 },
+  { col: 1, terrainType: "Hills", terrainClass: "Land", populationMultiplier: 0.7, productionMultiplier: 0.8, movementCostMultiplier: 1.8, defenseBonus: 0.33, minElevation: 0.2 },
+  { col: 2, terrainType: "Ice", terrainClass: "Ice", populationMultiplier: 0, productionMultiplier: 0, movementCostMultiplier: 4.0, defenseBonus: 0, minElevation: 0 },
+  { col: 3, terrainType: "Land", terrainClass: "Land", populationMultiplier: 1.0, productionMultiplier: 1.0, movementCostMultiplier: 1.0, defenseBonus: 0, minElevation: -0.08 },
+  { col: 4, terrainType: "Desert", terrainClass: "Land", populationMultiplier: 0.05, productionMultiplier: 0.2, movementCostMultiplier: 3.0, defenseBonus: 0, minElevation: -0.2 },
+  { col: 5, terrainType: "Sea", terrainClass: "Sea", populationMultiplier: 0, productionMultiplier: 0, movementCostMultiplier: 0, defenseBonus: 0, minElevation: 0 },
+  { col: 6, terrainType: "Mountain", terrainClass: "Land", populationMultiplier: 0.1, productionMultiplier: 0.8, movementCostMultiplier: 5.0, defenseBonus: 1.0, minElevation: 0.34 },
+  { col: 6, terrainType: "Tundra", terrainClass: "Land", populationMultiplier: 0.05, productionMultiplier: 0.2, movementCostMultiplier: 2.0, defenseBonus: 0, minElevation: 0 },
 ];

 // A city standing on a tile adds this fraction on top of the terrain's own
@@ -7,6 +7,7 @@
 export const PROTO_UNITS = [
  {
    id: "modern_infantry",
+    population: 1_000,
    name: "Modern infantry",
    maxHp: 500,
    cost: 100_000_000,
@@ -40,6 +41,7 @@ export const PROTO_UNITS = [
  },
  {
    id: "artillery",
+    materialUpkeep: { steel: 2, energy: 2000, hightech: 0 },
    name: "Artillery",
    maxHp: 400,
    cost: 300_000_000,
@@ -59,6 +61,8 @@ export const PROTO_UNITS = [
  },
  {
    id: "jet_fighter",
+    materialUpkeep: { steel: 5, energy: 5000, hightech: 1 },
+    advanced: true,
    name: "Jet fighter",
    maxHp: 300,
    cost: 400_000_000,
@@ -83,6 +87,8 @@ export const PROTO_UNITS = [
  },
  {
    id: "bomber",
+    materialUpkeep: { steel: 8, energy: 8000, hightech: 2 },
+    advanced: true,
    name: "Bomber",
    maxHp: 350,
    cost: 500_000_000,
@@ -106,6 +112,7 @@ export const PROTO_UNITS = [
  },
  {
    id: "battleship",
+    advanced: true,
    name: "Battleship",
    maxHp: 800,
    cost: 600_000_000,
@@ -123,6 +130,7 @@ export const PROTO_UNITS = [
  },
  {
    id: "mobile_radar",
+    advanced: true,
    name: "Mobile radar",
    maxHp: 200,
    cost: 50_000_000,
@@ -46,6 +46,9 @@ import { visibilityMethods } from "./game_state/visibility.js";
 import { serializationMethods } from "./game_state/serialization.js";
 import { monthlyMethods } from "./game_state/monthly.js";
 import { warfareMethods } from "./game_state/warfare.js";
+import { resourceMethods } from "./game_state/resources.js";
+import { budgetMethods } from "./game_state/budget.js";
+import { moneyMethods } from "./game_state/money.js";

 export {
  MAX_NEWS,
@@ -119,11 +122,11 @@ export class GameState {
    // railway lists are rebuilt only when something actually moved.
    this._improvementVersion = 0;
    this.tilePopulation = new Map();
-    // Per-tile GDP-per-capita multiplier, lowered by pillaging (default 1).
-    this.tileGdpPenalty = new Map();
-    // Absolute GDP-per-capita lost to fighting on a tile, and the hour its
+    // Per-tile production-per-head multiplier, lowered by pillaging (default 1).
+    this.tileProductionPenalty = new Map();
+    // Absolute production per head lost to fighting on a tile, and the hour its
    // recovery may begin. A tile leaves both maps once it has recovered.
-    this.tileBattleGdpDeficit = new Map();
+    this.tileBattleProductionDeficit = new Map();
    this.tileBattleRecoveryStart = new Map();
    this.budgets = new Map();
    this.training = new Map();
@@ -177,11 +180,11 @@ export class GameState {
    this._populationVersion = 0;
    this._ethnicityVersion = 0;
    this._visibleVersion = 0;
-    // Each land tile's opening GDP per capita, the constant natural growth is
-    // measured from. Static once the world exists.
-    this._gdpBaselineVersion = 0;
-    this._serializedGdpBaselineCache = null;
-    this.tileGdpBaseline = new Map();
+    // Each land tile's opening production per head, the constant natural growth
+    // is measured from. Static once the world exists.
+    this._productionBaselineVersion = 0;
+    this._serializedProductionBaselineCache = null;
+    this.tileProductionBaseline = new Map();
    // Approval is expensive to weight over every tile and is read far more
    // often than politics changes, so both the per-city and per-nation results
    // are memoised against the politics version (and cleared on territory
@@ -210,9 +213,9 @@ export class GameState {
    this._cityEconomyCache = new Map();
    this._cityEconomyCacheActive = false;
    // Per-civ factors that map generation picked so every nation starts with
-    // the same population and GDP per capita (see _balanceStartingEconomy).
+    // the same population and production per head (see _balanceStartingEconomy).
    this._populationBalance = new Map();
-    this._perCapitaBalance = new Map();
+    this._productionBalance = new Map();
    this._serializedTerritory = [];
    this._serializedExplored = new Map();
    this._serializedTileEthnicityCache = null;
@@ -259,6 +262,12 @@ export class GameState {
    // the browser rebuilds the very same islands.
    this.mapConfig = { ...this.mapConfig, nationCount: this.civilisations.length };
    this.seed = worldSeed !== 0 ? worldSeed | 0 : randomSeed();
+    // The small islands become the first capitals, so a nation's position in
+    // this list decides whether it starts island-bound. Shuffle the countries
+    // from the world seed so the same few nations are not always the ones
+    // seeded onto the islands. Players pick their nation from this same order,
+    // and the snapshot ships it, so client and server stay in step.
+    new Random((this.seed ^ 0x1b873593) >>> 0).shuffle(this.civilisations);
    // Combat rolls (a city losing a building level to a bombardment) draw from
    // their own generator, seeded from the world so a game is reproducible.
    this._combatRng = new Random((this.seed ^ 0x5bd1e995) >>> 0);
@@ -277,11 +286,13 @@ export class GameState {
    this._configured = true;

    this._placeSettlements();
+    this._initResources();
+    this._initMoney();
    this._refreshStatuses();
    this._revealAll();
    this._refreshVisibility();
    this._initMonthly();
-    this._initNaturalGdpGrowth();
+    this._initNaturalProductionGrowth();
    this._visibilityDirty = false;
    this._emitChanged();
  }
@@ -339,7 +350,7 @@ export class GameState {

  tickHour() {
    this.totalHours += 1;
-    // Natural growth is a whole number of days, so the cached per-capita figures
+    // Natural growth is a whole number of days, so the cached production figures
    // only go stale when a new day begins.
    if (this.totalHours % HOURS_PER_DAY === 0) this._gdpPerCapitaCache.clear();
    this._tickMonthly();
@@ -357,8 +368,12 @@ export class GameState {
      this._tickPopulation();
      this._tickPolitics();
      this._tickBattleTiles();
-      this._tickGdpRecovery();
+      this._tickProductionRecovery();
+      this._tickMoney();
      this._tickEconomy();
+      this._tickResources();
+      this._tickRepairs();
+      this._tickUnitSupply();
      this._refreshStatuses();
      this._applyDailyStatusEffects();
      this._resolveCombatRound();
@@ -392,5 +407,8 @@ Object.assign(
  visibilityMethods,
  serializationMethods,
  monthlyMethods,
-  warfareMethods
+  warfareMethods,
+  resourceMethods,
+  budgetMethods,
+  moneyMethods
 );
@@ -5,6 +5,7 @@
 import { key } from "../hex.js";
 import { AIR_DEFENSE, AIR_STRIKE, BOMBARD, CITY_BOMBARD } from "../data/combat.js";
 import { BUILDING_MECHANIC } from "../data/buildings.js";
+import { RESOURCE_RULES } from "../data/resources.js";

 export const airMethods = {
  // ----------------------------------------------------- building rules --
@@ -210,13 +211,15 @@ export const airMethods = {
    }
    const perCapita = this.getTileGdpPerCapita(city.coords);
    if (perCapita > 0) {
-      const deficit = (this.tileBattleGdpDeficit.get(k) || 0) + perCapita * 0.1;
-      this.tileBattleGdpDeficit.set(k, deficit);
+      const deficit = (this.tileBattleProductionDeficit.get(k) || 0) + perCapita * 0.1;
+      this.tileBattleProductionDeficit.set(k, deficit);
      this.tileBattleRecoveryStart.set(k, this.totalHours + 30 * 24);
      this._gdpPerCapitaCache.delete(k);
    }
    this._damageTileImprovement(city.coords, Math.max(1, Math.round(amount * 0.1)));
    this._razeCityBuildings(city, amount);
+    // The people and their city need materials to put themselves right again.
+    this._recordRepairDebt(city.coords, amount);
    this._emitChanged();
  },

@@ -248,6 +251,9 @@ export const airMethods = {
      if (chance > 0 && this._random() < chance) {
        if (level <= 1) delete city.buildings[index];
        else city.buildings[index] = level - 1;
+        // The level is not lost for good: it waits to be rebuilt once its
+        // materials are paid for.
+        this._queueCityRepair(city, Number(index), level);
        razed = true;
      }
    }
@@ -266,6 +272,9 @@ export const airMethods = {
    if (!city || city.civ === unit.civ) return false;
    const level = this._cityMechanicLevel(city, BUILDING_MECHANIC.AIR_DEFENSE);
    if (level <= 0) return false;
+    // Air defense is cheap to keep ready and costly to fire: no ammunition,
+    // no volley.
+    if (!this.payCombatResources(city.civ, "airDefenseVolley", level)) return false;
    const damage = Math.max(1, Math.round(AIR_DEFENSE.damagePerLevel * level));
    unit.hp -= damage;
    if (unit.hp > 0) return false;
@@ -384,8 +393,8 @@ export const airMethods = {
      if (path.length < 2) return false;
      paths.push(path);
    }
-    const cost = (AIR_STRIKE.cost || 0) * units.length;
-    if (cost > 0 && !this._spendBudget(civ, cost)) return false;
+    // A sortie is paid for in munitions, not money: no materials, no strike.
+    if (!this.payCombatResources(civ, "airStrike", units.length)) return false;
    this._declareWar(civ, target ? target.civ : city.civ);
    units.forEach((unit, index) => {
      unit.path = paths[index];
@@ -436,7 +445,11 @@ export const airMethods = {
        // No garrison left: the battery shells the city itself.
        const city = this._strikeCityAt(goal, unit.civ);
        if (city && this._strikeReady(unit, goal)) {
-          this._bombardCity(city, Math.max(1, Math.round(this._unitAttack(unit) * (BOMBARD.hourlyDamageFraction || 0) * 10)));
+          if (!this.payCombatResources(unit.civ, "artilleryVolley", 1)) {
+            unit.strikeTarget = null;
+          } else {
+            this._bombardCity(city, Math.max(1, Math.round(this._unitAttack(unit) * (BOMBARD.hourlyDamageFraction || 0) * 10)));
+          }
        } else {
          unit.strikeTarget = null;
        }
@@ -446,6 +459,11 @@ export const airMethods = {
        unit.strikeTarget = null;
        continue;
      }
+      // Each hourly volley is a shell spent.
+      if (!this.payCombatResources(unit.civ, "artilleryVolley", 1)) {
+        unit.strikeTarget = null;
+        continue;
+      }
      const full = this._unitAttack(unit) - this._effectiveDefense(target, true, this.unitProto(unit));
      const amount = Math.max(1, Math.round(full * (BOMBARD.hourlyDamageFraction || 0)));
      damage.set(target, (damage.get(target) || 0) + amount);
@@ -461,9 +479,13 @@ export const airMethods = {
  // ---------------------------------------------------------- training --

  // Places a freshly trained unit: aircraft and land units appear in the city,
-  // while a warship is launched onto the least crowded adjacent sea tile.
+  // while a warship is launched onto the least crowded adjacent sea tile. The
+  // unit's soldiers are drawn at random from the region's people.
  _spawnTrainedUnit(city, proto) {
-    return this._spawnUnit(this._spawnCoordsFor(city, proto), city.civ, proto, city.id);
+    const unit = this._spawnUnit(this._spawnCoordsFor(city, proto), city.civ, proto, city.id);
+    const soldiers = proto.population || RESOURCE_RULES.unitPopulation;
+    if (soldiers > 0) this.drawRegionPopulation(city, soldiers);
+    return unit;
  },

  _spawnCoordsFor(city, proto) {
@@ -0,0 +1,176 @@
+// The monthly budget ledger. Money moves in and out of a nation's treasury all
+// day; this keeps a running total for the calendar month, filed under the
+// expense categories the budget screen shows, so the panel can report what the
+// current month has cost so far and what each past month cost.
+//
+// Two figures are kept per category. `cash` is the money that actually left the
+// treasury; `economic` is the market value of the materials the category
+// consumed, whether they were drawn from the nation's stores or bought -- the
+// upkeep rows consume stock for free, so their economic cost is the truer
+// measure of what they took. Income and resource sales are the positive side.
+//
+// On every calendar-month rollover the live ledger is frozen into the history
+// and a fresh one begins, so the panel can page back through the last two years.
+
+import { BUDGET_EXPENSE_CATEGORIES } from "../data/economy.js";
+import { MONTH_NAMES } from "../game_clock.js";
+
+// How many completed months the history keeps. Two years is enough to compare a
+// season with the one before it without growing the snapshot without bound.
+export const BUDGET_HISTORY_MONTHS = 24;
+
+function emptyBudgetLedger() {
+  const cash = { income: 0, sell: 0 };
+  const economic = {};
+  for (const category of BUDGET_EXPENSE_CATEGORIES) {
+    cash[category.id] = 0;
+    economic[category.id] = 0;
+  }
+  // Money spent per category, broken down by the resource it bought, so an
+  // expense row can expand to show what it consumed and what it paid.
+  const resourceByCategory = {};
+  for (const category of BUDGET_EXPENSE_CATEGORIES) resourceByCategory[category.id] = {};
+  return { cash, economic, resourceBuy: {}, resourceSell: {}, resourceByCategory };
+}
+
+export const budgetMethods = {
+  _initBudgetHistory() {
+    this.budgetLedger = new Map();
+    for (let civ = 0; civ < this.civilisations.length; civ++) {
+      this.budgetLedger.set(civ, emptyBudgetLedger());
+    }
+    // Frozen months, oldest first: [{ monthIndex, records: [ledger, ...] }].
+    this.budgetHistory = [];
+  },
+
+  _budgetRecord(civ) {
+    if (!this.budgetLedger) this._initBudgetHistory();
+    let record = this.budgetLedger.get(civ);
+    if (!record) {
+      record = emptyBudgetLedger();
+      this.budgetLedger.set(civ, record);
+    }
+    return record;
+  },
+
+  // A signed cash movement for the month: positive is money into the treasury
+  // (tax, a resource sale, a refund), negative is money spent. Recorded once per
+  // category so the report can total them.
+  _recordBudgetCash(civ, category, amount) {
+    if (civ < 0 || !(amount !== 0)) return;
+    const record = this._budgetRecord(civ);
+    record.cash[category] = (record.cash[category] || 0) + amount;
+  },
+
+  // The market value of the materials one category consumed, whatever their
+  // source, so an upkeep row can show what it cost even when the stores paid.
+  _recordBudgetEconomic(civ, category, amount) {
+    if (civ < 0 || !(amount > 0)) return;
+    const record = this._budgetRecord(civ);
+    record.economic[category] = (record.economic[category] || 0) + amount;
+  },
+
+  // The money one expense category spent on one resource, so the row can be
+  // expanded to show what it bought.
+  _recordBudgetCategoryResource(civ, category, resource, amount) {
+    if (civ < 0 || !(amount > 0)) return;
+    const record = this._budgetRecord(civ);
+    const byResource = record.resourceByCategory[category]
+      || (record.resourceByCategory[category] = {});
+    byResource[resource] = (byResource[resource] || 0) + amount;
+  },
+
+  // The money a nation spent buying and earned selling one resource to the
+  // world market or another country, for the month's resource-trade memo.
+  _recordBudgetResource(civ, resource, bought, sold) {
+    if (civ < 0) return;
+    const record = this._budgetRecord(civ);
+    if (bought > 0) record.resourceBuy[resource] = (record.resourceBuy[resource] || 0) + bought;
+    if (sold > 0) record.resourceSell[resource] = (record.resourceSell[resource] || 0) + sold;
+  },
+
+  // Freezes the month that just ended and starts a new ledger. Called from the
+  // monthly rollover with the month index that is being closed.
+  _rolloverBudget(previousIndex) {
+    if (!this.budgetLedger) return;
+    const records = [];
+    for (let civ = 0; civ < this.civilisations.length; civ++) {
+      records.push(this.budgetLedger.get(civ) || emptyBudgetLedger());
+    }
+    this.budgetHistory.push({ monthIndex: previousIndex, records });
+    while (this.budgetHistory.length > BUDGET_HISTORY_MONTHS) this.budgetHistory.shift();
+    this.budgetLedger = new Map();
+    for (let civ = 0; civ < this.civilisations.length; civ++) {
+      this.budgetLedger.set(civ, emptyBudgetLedger());
+    }
+  },
+
+  // Every month the panel may show, oldest first, with the live month last.
+  budgetMonthReports(civ) {
+    const reports = [];
+    for (const entry of this.budgetHistory || []) {
+      reports.push(this._budgetReport(civ, entry.monthIndex, entry.records[civ], false));
+    }
+    const currentIndex = this._monthIndexOf(this.totalHours);
+    reports.push(this._budgetReport(
+      civ,
+      currentIndex,
+      this.budgetLedger ? this.budgetLedger.get(civ) : null,
+      true
+    ));
+    return reports;
+  },
+
+  _budgetReport(civ, monthIndex, record, isCurrent) {
+    const cash = (record && record.cash) || {};
+    const economic = (record && record.economic) || {};
+    const expenses = [];
+    let totalCash = 0;
+    let totalEconomic = 0;
+    const resourceByCategory = (record && record.resourceByCategory) || {};
+    for (const category of BUDGET_EXPENSE_CATEGORIES) {
+      const spent = Math.max(0, -(cash[category.id] || 0));
+      const cost = Math.max(0, economic[category.id] || 0, spent);
+      if (spent === 0 && cost === 0) continue;
+      const buys = Object.entries(resourceByCategory[category.id] || {})
+        .filter(([, amount]) => amount > 0)
+        .sort((a, b) => b[1] - a[1]);
+      expenses.push({
+        id: category.id,
+        label: category.label,
+        group: category.group,
+        cash: spent,
+        economic: cost,
+        buys,
+      });
+      totalCash += spent;
+      totalEconomic += cost;
+    }
+    const resourceBuy = (record && record.resourceBuy) || {};
+    const resourceSell = (record && record.resourceSell) || {};
+    const resourceIds = new Set([...Object.keys(resourceBuy), ...Object.keys(resourceSell)]);
+    const resourceTrade = Array.from(resourceIds)
+      .map((id) => ({
+        id,
+        bought: Math.max(0, resourceBuy[id] || 0),
+        sold: Math.max(0, resourceSell[id] || 0),
+      }))
+      .filter((entry) => entry.bought > 0 || entry.sold > 0);
+    const income = cash.income || 0;
+    const sales = cash.sell || 0;
+    const year = Math.floor(monthIndex / 12);
+    const month = monthIndex % 12;
+    return {
+      monthIndex,
+      isCurrent,
+      label: `${MONTH_NAMES[month]} ${year}`,
+      income,
+      sales,
+      expenses,
+      resourceTrade,
+      totalCash,
+      totalEconomic,
+      net: income + sales - totalCash,
+    };
+  },
+};
@@ -359,8 +359,8 @@ export const combatMethods = {
  },

  // Every tile where a battle is raging loses a share of its population and its
-  // GDP per capita each day, and its recovery clock is pushed back to 30 days
-  // after the last day of fighting.
+  // production per head each day, and its recovery clock is pushed back to 30
+  // days after the last day of fighting.
  _tickBattleTiles() {
    this._populationVersion += 1;
    for (const battle of this._battleTiles()) {
@@ -372,11 +372,11 @@ export const combatMethods = {
        this._recordBattleCivilianCasualties(battle, removed);
      }
      const perCapita = this.getTileGdpPerCapita(battle.coords);
-      let scarred = this.tileBattleGdpDeficit.has(k);
+      let scarred = this.tileBattleProductionDeficit.has(k);
      if (perCapita > 0) {
-        const deficit = (this.tileBattleGdpDeficit.get(k) || 0) +
-          perCapita * BATTLE.gdpPerCapitaLossPerDay;
-        this.tileBattleGdpDeficit.set(k, deficit);
+        const deficit = (this.tileBattleProductionDeficit.get(k) || 0) +
+          perCapita * BATTLE.productionLossPerDay;
+        this.tileBattleProductionDeficit.set(k, deficit);
        this._gdpPerCapitaCache.delete(k);
        scarred = true;
      }
@@ -391,18 +391,21 @@ export const combatMethods = {
    }
  },

-  // Once a battlefield has been quiet for `recoveryDelayDays`, its GDP per
-  // capita climbs back by `recoveryPerDay` a day until the scar is gone.
-  _tickGdpRecovery() {
-    for (const [k, deficit] of Array.from(this.tileBattleGdpDeficit)) {
+  // Once a battlefield has been quiet for `recoveryDelayDays`, its production
+  // per head climbs back by `recoveryPerDay` a day until the scar is gone.
+  _tickProductionRecovery() {
+    for (const [k, deficit] of Array.from(this.tileBattleProductionDeficit)) {
      const start = this.tileBattleRecoveryStart.get(k);
      if (start === undefined || this.totalHours < start) continue;
+      // A tile still carrying battle damage it has not paid to repair does not
+      // recover: the materials come first.
+      if ((this.tileRepairDebt.get(k) || 0) > 0.0001) continue;
      const remaining = deficit - BATTLE.recoveryPerDay;
      if (remaining <= 0) {
-        this.tileBattleGdpDeficit.delete(k);
+        this.tileBattleProductionDeficit.delete(k);
        this.tileBattleRecoveryStart.delete(k);
      } else {
-        this.tileBattleGdpDeficit.set(k, remaining);
+        this.tileBattleProductionDeficit.set(k, remaining);
      }
      this._gdpPerCapitaCache.delete(k);
    }
@@ -2,8 +2,9 @@
 // research/culture accrual and the daily economic ticks.

 import { ECONOMY } from "../data/economy.js";
+import { RESOURCE_RULES, RESOURCE_IDS } from "../data/resources.js";
 import {
-  EFFECT_GDP,
+  EFFECT_PRODUCTION,
  EFFECT_BUDGET_INCOME,
  EFFECT_RESEARCH,
  EFFECT_CULTURE,
@@ -16,15 +17,20 @@ import { technologyCost, technologyById } from "../data/technologies.js";
 import { NEWS_TECHNOLOGY } from "../data/relations.js";
 import {
  buildingUpkeep,
-  gdpPerCapitaFactors,
-  gdpPerCapitaFromFactors,
+  productionFactors,
+  productionFromFactors,
  governmentEffects,
  prerequisitesMet,
  technologyEffects,
 } from "../rules.js";
 import { key, parseKey } from "../hex.js";
-import { TRANSPORT_BY_ID } from "../data/improvements.js";
-import { HOURS_PER_DAY, HOURS_PER_YEAR } from "./constants.js";
+import {
+  TRANSPORT_BY_ID,
+  tileImprovementById,
+  isResourceTileBuilding,
+} from "../data/improvements.js";
+import { tileFoodOutput } from "../resources.js";
+import { HOURS_PER_DAY, HOURS_PER_YEAR, DAYS_PER_YEAR } from "./constants.js";
 import { effectAt, mergeModifiers } from "./helpers.js";

 export const economyMethods = {
@@ -36,22 +42,22 @@ export const economyMethods = {

  // The live economy: the raw sums over the civ's territory, adjusted by the
  // balancing factors map generation assigned so every civilisation starts with
-  // the same population and GDP per capita. The factors stay applied as the raw
-  // figures grow, so terrain and war keep shaping the economy without ever
-  // recreating the arbitrary starting gap.
+  // the same population and production per head. The factors stay applied as
+  // the raw figures grow, so terrain and war keep shaping the economy without
+  // ever recreating the arbitrary starting gap.
  _playerAggregates(civ) {
    const base = this._basePlayerAggregates(civ);
    const populationScale = this._populationBalance.get(civ) || 1;
-    const perCapitaScale = this._perCapitaBalance.get(civ) || 1;
+    const productionScale = this._productionBalance.get(civ) || 1;
    return {
      population: base.population * populationScale,
-      gdp: base.gdp * populationScale * perCapitaScale,
+      gdp: base.gdp * populationScale * productionScale,
    };
  },

  // The economy exactly as the tiles describe it, before balancing. Every
  // tile's per-capita figure already carries its region's and its nation's
-  // modifiers, so the sum needs no further adjustment.
+  // production modifiers, so the sum needs no further adjustment.
  _basePlayerAggregates(civ) {
    let population = 0;
    let baseGdp = 0;
@@ -73,60 +79,103 @@ export const economyMethods = {
    const region = city || this.regionCityAt(coords);
    const regional = region ? this.getCityBuildingModifiers(region) : null;
    const national = this.getNationalModifiers(owner);
-    const factors = gdpPerCapitaFactors(this.tiles[k], {
+    const factors = productionFactors(this.tiles[k], {
      cityKind: city ? (city.isCapital ? "capital" : "city") : null,
      nextToCity: !city && this._isNextToCity(coords, owner),
-      pillagePenalty: this.tileGdpPenalty.get(k) !== undefined ? this.tileGdpPenalty.get(k) : 1,
+      pillagePenalty: this.tileProductionPenalty.get(k) !== undefined
+        ? this.tileProductionPenalty.get(k)
+        : 1,
      // Fighting scars the tile too, but that loss recovers over time.
-      battleDeficit: this.tileBattleGdpDeficit.get(k) || 0,
+      battleDeficit: this.tileBattleProductionDeficit.get(k) || 0,
      trench: this.trenches.has(k),
-      regionalMultiplier: 1 + ((regional && regional[EFFECT_GDP]) || 0),
+      regionalMultiplier: 1 + ((regional && regional[EFFECT_PRODUCTION]) || 0),
      regionalLabel: region ? region.name : null,
-      nationalMultiplier: 1 + (national[EFFECT_GDP] || 0),
-      portGdp: this._regionPortGdp(region),
-      naturalGrowth: this._naturalTileGdpGrowth(k),
+      nationalMultiplier: 1 + (national[EFFECT_PRODUCTION] || 0),
+      portProduction: this._regionPortProduction(region),
+      naturalGrowth: this._naturalTileProductionGrowth(k),
    });
-    const perCapita = gdpPerCapitaFromFactors(ECONOMY.baseGdpPerCapita, factors);
+    const perCapita = productionFromFactors(this._regionProductionPerCapita(region), factors);
    this._gdpPerCapitaCache.set(k, perCapita);
    return perCapita;
  },

-  // Snapshots every land tile's opening GDP per capita, so natural growth has a
+  // GDP does not start from an abstract base figure: the ground a region covers
+  // produces resources, and their value on the market is what its people make.
+  // The base the production modifiers scale is that regional production, in
+  // euro a year, per head. It carries no city, port or terrain bonus of its own
+  // -- those stay in `productionFactors`, applied on top.
+  _regionProductionPerCapita(region) {
+    if (!region) return 0;
+    const cachedKey = `regionbase:${region.id}`;
+    if (this._gdpPerCapitaCache.has(cachedKey)) return this._gdpPerCapitaCache.get(cachedKey);
+    let population = 0;
+    for (const coords of this.regionTiles(region)) {
+      population += this.tilePopulation.get(key(coords.x, coords.y)) || 0;
+    }
+    const base = population > 0 ? this._regionProductionValue(region) / population : 0;
+    this._gdpPerCapitaCache.set(cachedKey, base);
+    return base;
+  },
+
+  // The market value of everything made across a region in a year: the food its
+  // worked land grows (from the land, not the headcount) plus the output of
+  // every resource building on it, each at the current world price.
+  _regionProductionValue(region) {
+    let daily = 0;
+    const foodMultiplier = this._regionFoodMultiplier(region);
+    for (const coords of this.regionTiles(region)) {
+      const k = key(coords.x, coords.y);
+      const tile = this.tiles[k];
+      if (!tile) continue;
+      const population = this.tilePopulation.get(k) || 0;
+      if (population > 0) {
+        daily += tileFoodOutput(tile) * foodMultiplier * this.getResourcePrice("food");
+      }
+      const id = this.tileImprovements.get(k);
+      const proto = id ? tileImprovementById(id) : null;
+      if (isResourceTileBuilding(proto)) {
+        daily += (proto.outputPerDay || 0) * this.getResourcePrice(proto.resource);
+      }
+    }
+    return daily * DAYS_PER_YEAR;
+  },
+
+  // Snapshots every land tile's opening production, so natural growth has a
  // constant to build on. The world and its economy must exist by now.
-  _initNaturalGdpGrowth() {
-    this.tileGdpBaseline = new Map();
-    if (ECONOMY.naturalGdpGrowthPerDay <= 0) return;
+  _initNaturalProductionGrowth() {
+    this.tileProductionBaseline = new Map();
+    if (ECONOMY.naturalProductionGrowthPerDay <= 0) return;
    for (const k in this.tiles) {
      const coords = parseKey(k);
      if (!this._isLand(coords)) continue;
      const perCapita = this.getTileGdpPerCapita(coords);
-      if (perCapita > 0) this.tileGdpBaseline.set(k, perCapita);
+      if (perCapita > 0) this.tileProductionBaseline.set(k, perCapita);
    }
    this._gdpPerCapitaCache.clear();
  },

-  // The flat amount a tile's GDP per capita has gained since January 2000: its
-  // opening figure times the daily rate, once per day elapsed. A constant, so
-  // the relative growth rate falls as the tile grows richer.
-  _naturalTileGdpGrowth(k) {
-    const baseline = this.tileGdpBaseline ? this.tileGdpBaseline.get(k) : 0;
+  // The flat amount a tile's production per head has gained since January 2000:
+  // its opening figure times the daily rate, once per day elapsed. A constant,
+  // so the relative growth rate falls as the tile grows richer.
+  _naturalTileProductionGrowth(k) {
+    const baseline = this.tileProductionBaseline ? this.tileProductionBaseline.get(k) : 0;
    if (!baseline) return 0;
-    return baseline * ECONOMY.naturalGdpGrowthPerDay * this._gdpGrowthDays();
+    return baseline * ECONOMY.naturalProductionGrowthPerDay * this._productionGrowthDays();
  },

-  _gdpGrowthDays() {
+  _productionGrowthDays() {
    return Math.floor(Math.max(0, this.totalHours) / HOURS_PER_DAY);
  },

-  // The flat GDP per capita a region's ports add to every tile it covers:
+  // The flat production per head a region's ports add to every tile it covers:
  // 1000 per level for each sea tile beside the city, summed over its ports.
-  _regionPortGdp(region) {
+  _regionPortProduction(region) {
    if (!region) return 0;
    let bonus = 0;
    for (const [index, level] of Object.entries(region.buildings || {})) {
      const proto = this.protoBuildings[index];
-      if (proto && proto.mechanic === BUILDING_MECHANIC.PORT_GDP) {
-        bonus += (proto.gdpPerCapitaPerSeaTilePerLevel || 0) * level;
+      if (proto && proto.mechanic === BUILDING_MECHANIC.PORT_PRODUCTION) {
+        bonus += (proto.productionPerSeaTilePerLevel || 0) * level;
      }
    }
    if (bonus === 0) return 0;
@@ -138,8 +187,32 @@ export const economyMethods = {
    return bonus * sea;
  },

+  // The extra food a region's ports bring in, as a multiplier on its tiles'
+  // output: each port level adds `foodPerSeaTilePerLevel` for every sea tile
+  // beside the port city. Returns 1 when the region has no port, so the common
+  // inland case is free.
+  _regionFoodMultiplier(region) {
+    if (!region) return 1;
+    let bonus = 0;
+    for (const [index, level] of Object.entries(region.buildings || {})) {
+      const proto = this.protoBuildings[index];
+      if (proto && proto.mechanic === BUILDING_MECHANIC.PORT_PRODUCTION) {
+        bonus += (proto.foodPerSeaTilePerLevel || 0) * level;
+      }
+    }
+    if (bonus === 0) return 1;
+    let sea = 0;
+    for (const neighbour of this._neighbours(region.coords)) {
+      const tile = this.tiles[key(neighbour.x, neighbour.y)];
+      if (tile && tile.terrainClass === "Sea") sea += 1;
+    }
+    return 1 + bonus * sea;
+  },
+
  getTileGdp(coords) {
-    return (this.tilePopulation.get(key(coords.x, coords.y)) || 0) * this.getTileGdpPerCapita(coords);
+    // The population is rounded, as everywhere it is shown, so a tile's GDP is
+    // exactly its shown people times its shown production per head.
+    return this.getTilePopulation(coords) * this.getTileGdpPerCapita(coords);
  },

  getPlayerGdp(civ) {
@@ -147,21 +220,28 @@ export const economyMethods = {
  },

  getPlayerUpkeep(civ) {
-    let total = this.getBuildingUpkeep(civ);
-    const battle = this._battleUnitIds();
-    for (const unit of this.units) {
-      if (unit.civ !== civ) continue;
-      const proto = this.unitProto(unit);
-      if (!proto) continue;
-      const statuses = this._effectiveStatuses(unit, battle.has(unit.id));
-      total += proto.upkeep * this._statusUpkeepMultiplier(statuses);
+    // Money upkeep is now only propaganda. Everything physical -- buildings,
+    // units, works, transport -- is maintained in materials and settled by the
+    // daily resource tick, so it never appears as a direct money bill.
+    return this.getCampaignUpkeep(civ);
+  },
+
+  // The maintenance materials one nation's buildings wear out in a day, for the
+  // budget forecast and the resources panel.
+  getBuildingUpkeep(civ) {
+    const total = { steel: 0, energy: 0, hightech: 0 };
+    for (const city of this.cities) {
+      if (city.civ !== civ) continue;
+      for (const [indexStr, level] of Object.entries(city.buildings || {})) {
+        if (level <= 0) continue;
+        const proto = this.protoBuildings[Number(indexStr)];
+        if (!proto) continue;
+        const costs = this.buildingUpkeepResources(proto, level);
+        total.steel += costs.steel;
+        total.energy += costs.energy;
+        total.hightech += costs.hightech;
+      }
    }
-    // Running propaganda campaigns are upkeep too, paid hour by hour.
-    total += this.getCampaignUpkeep(civ);
-    // The transport network and military tile improvements cost an hourly
-    // maintenance per tile and structure held.
-    total += this.getTransportUpkeep(civ);
-    total += this.getTileImprovementUpkeep(civ);
    return total;
  },

@@ -180,12 +260,12 @@ export const economyMethods = {
    return counts;
  },

-  // The hourly maintenance of a nation's transport network: every road tile it
-  // holds costs a flat fee, every railway tile three times as much.
+  // The daily steel a nation's transport network wears out: every road tile a
+  // little, every railway tile more.
  getTransportUpkeep(civ) {
    const counts = this._transportTiles(civ);
-    return counts.road * TRANSPORT_BY_ID.road.maintenance +
-      counts.railway * TRANSPORT_BY_ID.railway.maintenance;
+    return counts.road * RESOURCE_RULES.transportUpkeepSteel.road +
+      counts.railway * RESOURCE_RULES.transportUpkeepSteel.railway;
  },

  // The road and railway lines of the budget breakdown, dropping any empty kind.
@@ -193,34 +273,34 @@ export const economyMethods = {
    const counts = this._transportTiles(civ);
    const sources = [];
    if (counts.road > 0) {
+      const steel = counts.road * RESOURCE_RULES.transportUpkeepSteel.road;
      sources.push({
        label: TRANSPORT_BY_ID.road.name,
        kind: "transport",
        count: counts.road,
-        amount: counts.road * TRANSPORT_BY_ID.road.maintenance,
+        resources: { steel, energy: 0, hightech: 0 },
+        amount: this._upkeepCost({ steel }),
      });
    }
    if (counts.railway > 0) {
+      const steel = counts.railway * RESOURCE_RULES.transportUpkeepSteel.railway;
      sources.push({
        label: TRANSPORT_BY_ID.railway.name,
        kind: "transport",
        count: counts.railway,
-        amount: counts.railway * TRANSPORT_BY_ID.railway.maintenance,
+        resources: { steel, energy: 0, hightech: 0 },
+        amount: this._upkeepCost({ steel }),
      });
    }
    return sources;
  },

-  getBuildingUpkeep(civ) {
-    let total = 0;
-    for (const city of this.cities) {
-      if (city.civ !== civ) continue;
-      for (const indexStr of Object.keys(city.buildings)) {
-        const index = Number(indexStr);
-        total += buildingUpkeep(this.protoBuildings[index], city.buildings[indexStr]);
-      }
-    }
-    return total;
+  // The market value of a day's upkeep materials: what the state would pay to
+  // buy them, which is what the budget panel forecasts.
+  _upkeepCost(costs) {
+    return (costs.steel || 0) * this.getResourcePrice("steel") +
+      (costs.energy || 0) * this.getResourcePrice("energy") +
+      (costs.hightech || 0) * this.getResourcePrice("hightech");
  },

  getCityBuildingLevel(city, protoIndex) {
@@ -250,9 +330,9 @@ export const economyMethods = {
    // civilisation's start equal; they scale the region figures too, so the
    // regions of a nation always add up to its headline population and GDP.
    const populationScale = this._populationBalance.get(city.civ) || 1;
-    const perCapitaScale = this._perCapitaBalance.get(city.civ) || 1;
+    const productionScale = this._productionBalance.get(city.civ) || 1;
    population *= populationScale;
-    gdp *= populationScale * perCapitaScale;
+    gdp *= populationScale * productionScale;
    const rate = ECONOMY.budgetGdpRate;
    const base = gdp * rate;
    const cityMods = this.getCityBuildingModifiers(city);
@@ -327,6 +407,14 @@ export const economyMethods = {
    const tileImprovementSources = this._tileImprovementUpkeepSources(civ);
    const tileImprovementUpkeep =
      tileImprovementSources.reduce((sum, source) => sum + source.amount, 0);
+    // What the nation spent buying and earned selling each resource over the
+    // last day, for the budget panel's trade section.
+    const record = this.resourceSpend.get(civ) || {};
+    const buy = record.buy || {};
+    const sell = record.sell || {};
+    const resourceMoney = RESOURCE_IDS
+      .map((id) => ({ id, bought: buy[id] || 0, sold: sell[id] || 0 }))
+      .filter((entry) => entry.bought > 0 || entry.sold > 0);
    return {
      income: { rate, base, modifier, total: income, sources: incomeSources, regions },
      buildingUpkeep: { total: buildingUpkeep, sources: buildingSources, groups },
@@ -338,6 +426,7 @@ export const economyMethods = {
        sources: tileImprovementSources,
        groups: tileImprovementSources,
      },
+      resourceMoney,
      net: income - buildingUpkeep - unitUpkeep - campaignUpkeep - transportUpkeep - tileImprovementUpkeep,
    };
  },
@@ -392,13 +481,17 @@ export const economyMethods = {
    for (const indexStr of Object.keys(city.buildings)) {
      const index = Number(indexStr);
      const level = city.buildings[indexStr];
-      const amount = buildingUpkeep(this.protoBuildings[index], level);
+      const proto = this.protoBuildings[index];
+      if (!proto || level <= 0) continue;
+      const resources = this.buildingUpkeepResources(proto, level);
+      const amount = this._upkeepCost(resources);
      if (amount === 0) continue;
      groups.push({
        index,
-        label: this.protoBuildings[index].name,
+        label: proto.name,
        amount,
-        cities: [{ cityId: city.id, cityName: city.name, level, amount }],
+        resources,
+        cities: [{ cityId: city.id, cityName: city.name, level, amount, resources }],
      });
    }
    return groups.sort((a, b) => b.amount - a.amount);
@@ -465,16 +558,23 @@ export const economyMethods = {
      for (const indexStr of Object.keys(city.buildings)) {
        const index = Number(indexStr);
        const level = city.buildings[indexStr];
-        const amount = buildingUpkeep(this.protoBuildings[index], level);
+        const proto = this.protoBuildings[index];
+        if (!proto || level <= 0) continue;
+        const resources = this.buildingUpkeepResources(proto, level);
+        const amount = this._upkeepCost(resources);
        if (amount === 0) continue;
        const group = byType.get(index) || {
          index,
-          label: this.protoBuildings[index].name,
+          label: proto.name,
          amount: 0,
+          resources: { steel: 0, energy: 0, hightech: 0 },
          cities: [],
        };
        group.amount += amount;
-        group.cities.push({ cityId: city.id, cityName: city.name, level, amount });
+        group.resources.steel += resources.steel;
+        group.resources.energy += resources.energy;
+        group.resources.hightech += resources.hightech;
+        group.cities.push({ cityId: city.id, cityName: city.name, level, amount, resources });
        byType.set(index, group);
      }
    }
@@ -488,6 +588,7 @@ export const economyMethods = {
      label: group.label,
      kind: "building",
      amount: group.amount,
+      resources: group.resources,
    }));
  },

@@ -497,10 +598,27 @@ export const economyMethods = {
    for (const unit of this.units) {
      if (unit.civ !== civ) continue;
      const proto = this.unitProto(unit);
-      if (!proto || !proto.upkeep) continue;
+      if (!proto) continue;
      const statuses = this._effectiveStatuses(unit, battle.has(unit.id));
-      const entry = sources.get(unit.proto) || { label: proto.name, kind: "unit", amount: 0, count: 0 };
-      entry.amount += proto.upkeep * this._statusUpkeepMultiplier(statuses);
+      const multiplier = this._statusUpkeepMultiplier(statuses);
+      const costs = this.unitUpkeepResources(proto);
+      const resources = {
+        steel: costs.steel * multiplier,
+        energy: 0,
+        hightech: costs.hightech * multiplier,
+      };
+      const amount = this._upkeepCost(resources);
+      if (amount === 0) continue;
+      const entry = sources.get(unit.proto) || {
+        label: proto.name,
+        kind: "unit",
+        amount: 0,
+        resources: { steel: 0, energy: 0, hightech: 0 },
+        count: 0,
+      };
+      entry.amount += amount;
+      entry.resources.steel += resources.steel;
+      entry.resources.hightech += resources.hightech;
      entry.count += 1;
      sources.set(unit.proto, entry);
    }
@@ -604,6 +722,13 @@ export const economyMethods = {
    return set ? set.has(index) : false;
  },

+  // Whether a nation knows a technology, by its catalogue id. Used to gate the
+  // things only late research unlocks (the fusion plant).
+  hasTechnology(civ, id) {
+    const index = this.technologies.findIndex((tech) => tech.id === id);
+    return index >= 0 && this.isResearched(civ, index);
+  },
+
  getResearchedIndices(civ) {
    const set = this.researched.get(civ) || new Set();
    return Array.from(set);
@@ -740,13 +865,38 @@ export const economyMethods = {

  // Deducts `amount` from a nation's budget, returning false (and charging
  // nothing) when it cannot afford it. A non-positive amount is always free.
-  _spendBudget(civ, amount) {
+  // When a `category` is given the spend is filed into the month's budget
+  // ledger, so the panel can report what each kind of outlay cost.
+  // The government can always pay: a spend is never refused for want of money.
+  // A treasury driven below zero is an overdraft, a debt owed to the central
+  // bank, and carries interest until the budget recovers.
+  _spendBudget(civ, amount, category = null) {
    if (amount <= 0) return true;
-    if (this.getBudget(civ) < amount) return false;
    this.budgets.set(civ, this.getBudget(civ) - amount);
+    // The money does not vanish: it is paid into the nation's regions, the
+    // private sector that supplied the goods, labour or services.
+    this._creditRegions(civ, amount);
+    if (category) this._recordBudgetCash(civ, category, -amount);
    return true;
  },

+  // How far a nation's treasury has been driven into the red, owed to its
+  // central bank.
+  getGovernmentDebt(civ) {
+    return Math.max(0, -this.getBudget(civ));
+  },
+
+  // Puts money back into the treasury, reversing a spend. With a category it
+  // cancels part of that category's month total, so a refunded order does not
+  // linger as an expense.
+  _refundBudget(civ, amount, category = null) {
+    if (!(amount > 0)) return;
+    this.budgets.set(civ, this.getBudget(civ) + amount);
+    // A refund claws the money back from the regions it was paid to.
+    this._chargeRegions(civ, amount);
+    if (category) this._recordBudgetCash(civ, category, amount);
+  },
+
  getTraining(cityId) {
    return this.training.get(cityId) || null;
  },
@@ -762,12 +912,62 @@ export const economyMethods = {
    this._populationVersion += 1;
  },

+  // The people living in one city's region, summed over its tiles.
+  regionPopulation(city) {
+    let total = 0;
+    for (const coords of this.regionTiles(city)) {
+      total += this.tilePopulation.get(key(coords.x, coords.y)) || 0;
+    }
+    return total;
+  },
+
+  // Pulls `amount` people out of a city's region into a unit, choosing the
+  // tiles at random in proportion to how many people each holds. Returns how
+  // many were actually drawn (never more than the region had).
+  drawRegionPopulation(city, amount) {
+    if (!(amount > 0)) return 0;
+    const tiles = [];
+    let total = 0;
+    for (const coords of this.regionTiles(city)) {
+      const k = key(coords.x, coords.y);
+      const population = this.tilePopulation.get(k) || 0;
+      if (population <= 0) continue;
+      tiles.push({ k, population });
+      total += population;
+    }
+    if (total <= 0) return 0;
+    const wanted = Math.min(amount, total);
+    let remaining = wanted;
+    while (remaining > 0 && tiles.length > 0) {
+      let pick = this._random() * total;
+      let index = 0;
+      for (; index < tiles.length - 1; index++) {
+        pick -= tiles[index].population;
+        if (pick <= 0) break;
+      }
+      const tile = tiles[index];
+      const take = Math.min(tile.population, remaining);
+      tile.population -= take;
+      total -= take;
+      remaining -= take;
+      this.tilePopulation.set(tile.k, tile.population);
+      if (tile.population <= 0) tiles.splice(index, 1);
+    }
+    this._populationVersion += 1;
+    return wanted;
+  },
+
  _tickEconomy() {
    const hours = HOURS_PER_DAY;
    for (const civ of Array.from(this.budgets.keys())) {
      const income = this.getCivHourlyIncome(civ) * hours;
      const upkeep = this.getPlayerUpkeep(civ) * hours;
-      this.budgets.set(civ, this.getBudget(civ) + income - upkeep);
+      // Tax is collected from the private sector, not minted, then the day's
+      // propaganda spending is paid back out to it.
+      this._chargeRegions(civ, income);
+      this.budgets.set(civ, this.getBudget(civ) + income);
+      this._recordBudgetCash(civ, "income", income);
+      if (upkeep > 0) this._spendBudget(civ, upkeep, "campaign");
    }
  },

@@ -777,7 +977,12 @@ export const economyMethods = {
      const scienceRate = modifiers[EFFECT_RESEARCH] || 0;
      const cultureRate = modifiers[EFFECT_CULTURE] || 0;
      if (scienceRate === 0 && cultureRate === 0) continue;
-      this._addResearch(civ, scienceRate);
+      // Science buildings spend a unit of high-tech for each research point
+      // they make, so a nation short of chips researches only as far as its
+      // store reaches. Government research needs no high-tech.
+      const buildingRate = this.getCivBuildingModifiers(civ)[EFFECT_RESEARCH] || 0;
+      const effectiveBuilding = this._spendHighTechForResearch(civ, buildingRate);
+      this._addResearch(civ, scienceRate - buildingRate + effectiveBuilding);
      this.culture.set(civ, this.getCulture(civ) + cultureRate);
    }
  },
@@ -877,13 +1082,55 @@ export const economyMethods = {
  },

  // Units resting inside one of their own cities recover a little health each
-  // in-game hour.
+  // in-game hour, at a materials cost -- steel for a ground or naval unit, plus
+  // high-tech for an aircraft or radar -- and by drawing replacement soldiers
+  // out of the region's civilians. A nation that can find neither does not heal.
  _tickGarrisonHealing() {
    for (const unit of this.units) {
      if (unit.hp >= unit.maxHp) continue;
      const city = this.cityAt(unit.coords);
      if (!city || city.civ !== unit.civ) continue;
-      unit.hp = Math.min(unit.maxHp, unit.hp + CITY_GARRISON_HEAL_PER_HOUR);
+      const proto = this.unitProto(unit);
+      if (!proto) continue;
+      const heal = Math.min(unit.maxHp - unit.hp, CITY_GARRISON_HEAL_PER_HOUR);
+      if (heal <= 0) continue;
+      // Each hit point restored is a share of the unit's soldiers made good from
+      // the city's people; without enough people, only part of the heal happens.
+      const soldiers = proto.population || RESOURCE_RULES.unitPopulation;
+      const soldierNeed = soldiers > 0 ? (heal / unit.maxHp) * soldiers : 0;
+      const available = this.regionPopulation(city);
+      const popFraction = soldierNeed > 0 ? Math.min(1, available / soldierNeed) : 1;
+      const targetHeal = heal * popFraction;
+      if (targetHeal <= 0) continue;
+      const repair = RESOURCE_RULES.repair;
+      const wanted = {
+        steel: targetHeal * repair.unitSteelPerHp,
+        hightech: proto.advanced ? targetHeal * repair.unitHighTechPerHp : 0,
+      };
+      const fromStock = this._drawFromNearest(city.civ, city.coords, wanted);
+      const shortfall = {
+        steel: wanted.steel - fromStock.steel,
+        hightech: wanted.hightech - fromStock.hightech,
+      };
+      const cost = this._marketUnitCost("steel") * shortfall.steel +
+        this._marketUnitCost("hightech") * shortfall.hightech;
+      const steelCost = this._marketUnitCost("steel") * shortfall.steel;
+      const techCost = this._marketUnitCost("hightech") * shortfall.hightech;
+      const paid = 1;
+      if (cost > 0) {
+        // The government can always pay, borrowing if the treasury is dry.
+        this._spendBudget(city.civ, cost * paid, "units");
+        this._recordResourceSpend(city.civ, "upkeep", cost * paid, {
+          steel: steelCost * paid,
+          hightech: techCost * paid,
+        });
+      }
+      const gained = targetHeal * paid;
+      if (gained > 0) {
+        unit.hp = Math.min(unit.maxHp, unit.hp + gained);
+        const drawn = soldiers > 0 ? (gained / unit.maxHp) * soldiers : 0;
+        if (drawn > 0) this.drawRegionPopulation(city, drawn);
+      }
    }
  },
 };
@@ -0,0 +1,497 @@
+// Money and currencies. Each nation issues its own currency; a central bank
+// sets an interest rate and holds foreign reserves. The private sector is the
+// regions: every region keeps its own cash reserve, a basket of currencies, and
+// chases profit trading with its neighbours.
+//
+// Stage 1 keeps every currency at par (value 1 against the global unit) and
+// every region's cash in its own national currency. Later stages let the rates
+// float, fill the baskets with foreign money and move real trade onto private
+// cash; the shapes here (baskets, reserves, rates) are already the final ones.
+
+import { MONEY } from "../data/economy.js";
+import { DAYS_PER_YEAR } from "./constants.js";
+
+const FALLBACK_CURRENCY = { code: "XAU", symbol: "¤", name: "Credit" };
+
+function emptyBasket() {
+  return new Map();
+}
+
+export const moneyMethods = {
+  // ------------------------------------------------------- setup --
+
+  _initMoney() {
+    this.regionCash = new Map();
+    // What each region owes its national central bank, in the national currency.
+    this.regionDebt = new Map();
+    // What each nation's central bank owes foreign central banks, by currency:
+    // the offsetting side of the currency it issues when it settles trade in a
+    // foreign seller's money.
+    this.centralBankDebt = new Map();
+    this.centralBankRate = new Map();
+    this.centralBankReserves = new Map();
+    this.currencyValues = new Map();
+    this._currencyDemand = new Map();
+    this._currencyCivMap = null;
+    for (let civ = 0; civ < this.civilisations.length; civ++) {
+      this.centralBankRate.set(civ, MONEY.defaultInterestRate);
+      this.centralBankReserves.set(civ, emptyBasket());
+      this.centralBankDebt.set(civ, emptyBasket());
+      this.currencyValues.set(civ, 1);
+      this._currencyDemand.set(civ, 0);
+    }
+    for (const city of this.cities) {
+      this.regionCash.set(city.id, this._openingRegionBasket(city));
+    }
+  },
+
+  // A region opens with a private-sector cash reserve in its nation's currency,
+  // sized off its yearly GDP.
+  _openingRegionBasket(city) {
+    const economy = this.getCityEconomy(city);
+    const cash = Math.max(0, economy.gdp) * MONEY.privateCashFraction;
+    return new Map([[this.currencyOf(city.civ).code, cash]]);
+  },
+
+  // ---------------------------------------------------- currencies --
+
+  currencyOf(civ) {
+    const civEntry = this.civilisations[civ];
+    return (civEntry && civEntry.currency) || FALLBACK_CURRENCY;
+  },
+
+  // The price of one unit of a nation's currency in global units. Every
+  // currency starts at par and floats from there.
+  currencyValue(civ) {
+    if (!this.currencyValues) return 1;
+    return this.currencyValues.get(civ) || 1;
+  },
+
+  setCurrencyValue(civ, value) {
+    const floor = 1 - MONEY.maxRateDrift;
+    const ceiling = 1 + MONEY.maxRateDrift;
+    this.currencyValues.set(civ, Math.max(floor, Math.min(ceiling, value)));
+  },
+
+  _civByCurrencyCode() {
+    if (!this._currencyCivMap) {
+      this._currencyCivMap = new Map();
+      this.civilisations.forEach((entry, index) => {
+        if (entry.currency) this._currencyCivMap.set(entry.currency.code, index);
+      });
+    }
+    return this._currencyCivMap;
+  },
+
+  currencyValueOf(code) {
+    const civ = this._civByCurrencyCode().get(code);
+    return civ === undefined ? 1 : this.currencyValue(civ);
+  },
+
+  // How many units of `toCiv`'s currency one unit of `fromCiv`'s buys.
+  exchangeRate(fromCiv, toCiv) {
+    if (fromCiv === toCiv) return 1;
+    return this.currencyValue(fromCiv) / this.currencyValue(toCiv);
+  },
+
+  // --------------------------------------------------- region cash --
+
+  // Takes `amount` of one currency out of a region's basket. Returns false (and
+  // charges nothing) when the region does not hold enough.
+  _debitRegionCash(city, code, amount) {
+    if (!(amount > 0)) return true;
+    const basket = this.regionCash ? this.regionCash.get(city.id) : null;
+    if (!basket) return false;
+    const held = basket.get(code) || 0;
+    if (held + 1e-9 < amount) return false;
+    basket.set(code, held - amount);
+    return true;
+  },
+
+  _creditRegionCash(city, code, amount) {
+    if (!(amount > 0)) return;
+    const basket = this.regionCash ? this.regionCash.get(city.id) : null;
+    if (!basket) return;
+    basket.set(code, (basket.get(code) || 0) + amount);
+  },
+
+  // Charges a region, spending its cash and borrowing whatever is missing from
+  // its national central bank at the bank's rate. A region never fails to pay:
+  // it takes on debt instead.
+  _chargeRegionCash(city, code, amount) {
+    if (!(amount > 0)) return true;
+    const basket = this.regionCash ? this.regionCash.get(city.id) : null;
+    if (!basket) return false;
+    const held = basket.get(code) || 0;
+    if (held >= amount) {
+      basket.set(code, held - amount);
+      return true;
+    }
+    basket.set(code, 0);
+    const shortfall = amount - held;
+    this.regionDebt.set(city.id, (this.regionDebt.get(city.id) || 0) + shortfall);
+    return true;
+  },
+
+  // Pays money into a nation's regions, split by population: the private sector
+  // is what ultimately receives government spending, so the money stays in the
+  // system rather than vanishing.
+  _creditRegions(civ, amount, code = null) {
+    if (!(amount > 0)) return;
+    const cities = this.cities.filter((city) => city.civ === civ);
+    if (cities.length === 0) return;
+    const currency = code || this.currencyOf(civ).code;
+    const shares = this._populationShares(cities);
+    for (let i = 0; i < cities.length; i++) {
+      this._creditRegionCash(cities[i], currency, amount * shares[i]);
+    }
+  },
+
+  // Takes money from a nation's regions, split by population, borrowing from the
+  // central bank where a region is short. This is how taxes are collected
+  // without minting money.
+  _chargeRegions(civ, amount) {
+    if (!(amount > 0)) return;
+    const cities = this.cities.filter((city) => city.civ === civ);
+    if (cities.length === 0) return;
+    const currency = this.currencyOf(civ).code;
+    const shares = this._populationShares(cities);
+    for (let i = 0; i < cities.length; i++) {
+      this._chargeRegionCash(cities[i], currency, amount * shares[i]);
+    }
+  },
+
+  // Pays the world market's producers -- every region outside the buyer's nation
+  // -- so an import does not drain money out of the world.
+  _payWorld(buyerCiv, amount, code) {
+    if (!(amount > 0)) return;
+    const others = this.cities.filter((city) => city.civ !== buyerCiv);
+    if (others.length === 0) {
+      this._creditRegions(buyerCiv, amount, code);
+      return;
+    }
+    const shares = this._populationShares(others);
+    for (let i = 0; i < others.length; i++) {
+      this._creditRegionCash(others[i], code, amount * shares[i]);
+    }
+  },
+
+  // Each region's share of a set's total population, defaulting to an even split
+  // when there are no people at all.
+  _populationShares(cities) {
+    let total = 0;
+    const populations = cities.map((city) => {
+      const people = this.regionPopulation(city);
+      total += people;
+      return people;
+    });
+    if (total <= 0) return cities.map(() => 1 / cities.length);
+    return populations.map((people) => people / total);
+  },
+
+  getRegionDebt(city) {
+    return this.regionDebt ? (this.regionDebt.get(city.id) || 0) : 0;
+  },
+
+  // Everything the nation's regions owe their central bank.
+  getRegionDebtTotal(civ) {
+    let total = 0;
+    for (const city of this.cities) {
+      if (city.civ === civ) total += this.getRegionDebt(city);
+    }
+    return total;
+  },
+
+  // The central bank's outstanding loans: the government's overdraft, every
+  // region's borrowing, and what it has issued to settle foreign trade.
+  getCentralBankLoans(civ) {
+    return this.getGovernmentDebt(civ) + this.getRegionDebtTotal(civ) +
+      this._centralBankDebtValue(civ);
+  },
+
+  // The city of `civ` nearest `coords`, so a sale to a resource building can be
+  // paid into the private cash of the region that owns it.
+  _regionCityNear(civ, coords) {
+    let best = null;
+    let bestDistance = Infinity;
+    for (const city of this.cities) {
+      if (city.civ !== civ) continue;
+      const distance = this.topology.tileDistance(city.coords, coords);
+      if (distance < bestDistance) {
+        bestDistance = distance;
+        best = city;
+      }
+    }
+    return best;
+  },
+
+  // --------------------------------------------------- central bank --
+
+  _addReserve(civ, code, amount) {
+    if (!(amount > 0)) return;
+    const reserves = this.centralBankReserves.get(civ)
+      || (this.centralBankReserves.set(civ, emptyBasket()), this.centralBankReserves.get(civ));
+    reserves.set(code, (reserves.get(code) || 0) + amount);
+  },
+
+  // The debt a central bank takes on when it issues its currency to settle a
+  // foreign seller's bill. It is the loan side of the money the sale created, so
+  // the world's money is conserved.
+  _addCentralBankDebt(civ, code, amount) {
+    if (!(amount > 0)) return;
+    let debts = this.centralBankDebt.get(civ);
+    if (!debts) {
+      debts = emptyBasket();
+      this.centralBankDebt.set(civ, debts);
+    }
+    debts.set(code, (debts.get(code) || 0) + amount);
+  },
+
+  getCentralBankDebt(civ) {
+    return this.centralBankDebt ? (this.centralBankDebt.get(civ) || emptyBasket()) : emptyBasket();
+  },
+
+  // What a central bank owes foreign banks, in its own currency.
+  _centralBankDebtValue(civ) {
+    const value = this.currencyValue(civ);
+    let total = 0;
+    for (const [code, amount] of this.getCentralBankDebt(civ)) {
+      total += amount * this.currencyValueOf(code) / value;
+    }
+    return total;
+  },
+
+  // A region buys `globalValue` (in global units) worth of `targetCiv`'s
+  // currency: first from what it already holds, then from that nation's central
+  // bank, paying with its own national currency (borrowing from its own bank if
+  // it is short). The target's central bank keeps the buyer's currency as a
+  // foreign reserve. Returns the amount of the target currency that ends up
+  // handed to the seller.
+  _regionAcquireCurrency(buyerCity, targetCiv, globalValue) {
+    if (!(globalValue > 0)) return { code: this.currencyOf(targetCiv).code, amount: 0 };
+    const target = this.currencyOf(targetCiv);
+    const buyer = this.currencyOf(buyerCity.civ);
+    const vTarget = this.currencyValue(targetCiv);
+    const vBuyer = this.currencyValue(buyerCity.civ);
+    const needTarget = globalValue / vTarget;
+    const basket = this.regionCash.get(buyerCity.id);
+    if (!basket) return null;
+    const heldTarget = basket.get(target.code) || 0;
+    const fromHeld = Math.min(heldTarget, needTarget);
+    const remaining = needTarget - fromHeld;
+    if (remaining > 0) {
+      const costBuyer = remaining * vTarget / vBuyer;
+      // The buyer pays with its national currency, borrowing the rest from its
+      // own central bank if it is short; the seller's bank holds that currency
+      // as a reserve and issues its own, taking on the matching debt so no money
+      // is conjured from nothing.
+      this._chargeRegionCash(buyerCity, buyer.code, costBuyer);
+      this._addReserve(targetCiv, buyer.code, costBuyer);
+      this._addCentralBankDebt(targetCiv, target.code, remaining);
+    }
+    if (fromHeld > 0) basket.set(target.code, heldTarget - fromHeld);
+    return { code: target.code, amount: fromHeld + remaining };
+  },
+
+  // --------------------------------------------------- demand/rates --
+
+  _recordCurrencyDemand(civ, amount) {
+    if (!this._currencyDemand || civ < 0 || !(amount !== 0)) return;
+    this._currencyDemand.set(civ, (this._currencyDemand.get(civ) || 0) + amount);
+  },
+
+  // All of a nation's currency in circulation, in global units: its own
+  // treasury, every region's holding and every central bank's reserve.
+  _currencyMass(civ) {
+    const code = this.currencyOf(civ).code;
+    const value = this.currencyValue(civ);
+    // An overdrawn treasury is a claim on the bank, not circulating money.
+    let amount = Math.max(0, this.getBudget(civ) || 0);
+    for (const city of this.cities) amount += this.getRegionCash(city).get(code) || 0;
+    for (const reserves of this.centralBankReserves.values()) {
+      amount += reserves.get(code) || 0;
+    }
+    return Math.max(1, amount * value);
+  },
+
+  // ----------------------------------------------------- holdings --
+
+  getRegionCash(city) {
+    if (!this.regionCash) return emptyBasket();
+    return this.regionCash.get(city.id) || emptyBasket();
+  },
+
+  getCentralBankReserves(civ) {
+    if (!this.centralBankReserves) return emptyBasket();
+    return this.centralBankReserves.get(civ) || emptyBasket();
+  },
+
+  getCentralBankRate(civ) {
+    if (!this.centralBankRate) return MONEY.defaultInterestRate;
+    const rate = this.centralBankRate.get(civ);
+    return rate === undefined ? MONEY.defaultInterestRate : rate;
+  },
+
+  setCentralBankRate(civ, rate) {
+    const value = Math.max(0, Math.min(MONEY.maxInterestRate, Number(rate) || 0));
+    this.centralBankRate.set(civ, value);
+  },
+
+  // A player sets the central bank's interest rate: the rate regions and the
+  // government borrow at, compounding on their debts.
+  requestSetInterestRate(civ, rate) {
+    if (civ < 0 || civ >= this.civilisations.length) return false;
+    const value = Number(rate);
+    if (!Number.isFinite(value) || value < 0) return false;
+    this.setCentralBankRate(civ, value);
+    this._emitChanged();
+    return true;
+  },
+
+  // The value of a basket in `inCiv`'s currency at the current rates.
+  _basketValue(basket, inCiv = 0) {
+    let total = 0;
+    const denom = this.currencyValue(inCiv);
+    for (const [code, amount] of basket) {
+      total += amount * this.currencyValueOf(code) / denom;
+    }
+    return total;
+  },
+
+  // The private-sector cash of one region, expressed in a nation's currency.
+  getRegionCashValue(city, inCiv = city.civ) {
+    return this._basketValue(this.getRegionCash(city), inCiv);
+  },
+
+  // Everything the private sector of a nation holds, in that nation's currency.
+  getPrivateSectorCash(civ, inCiv = civ) {
+    let total = 0;
+    for (const city of this.cities) {
+      if (city.civ !== civ) continue;
+      total += this._basketValue(this.getRegionCash(city), inCiv);
+    }
+    return total;
+  },
+
+  // --------------------------------------------------- daily tick --
+
+  // The day's monetary work: debts to the central bank accrue interest, regions
+  // repatriate any foreign money they still hold and pay down what they owe, and
+  // the day's trading leaves each currency's value drifting with net demand. The
+  // interest rate is the borrowing cost, not a direct inflation lever.
+  _tickMoney() {
+    if (!this.regionCash) return;
+    for (const city of this.cities) {
+      const basket = this.regionCash.get(city.id);
+      const rate = this.getCentralBankRate(city.civ) / DAYS_PER_YEAR;
+      // Interest compounds on whatever the region already owes.
+      const debt = this.regionDebt.get(city.id) || 0;
+      if (debt > 0) this.regionDebt.set(city.id, debt * (1 + rate));
+      if (!basket) continue;
+      this._repatriateRegion(city, basket);
+      this._repayRegionDebt(city, basket);
+    }
+    for (let civ = 0; civ < this.civilisations.length; civ++) {
+      // A treasury in the red is an overdraft that compounds too.
+      const budget = this.getBudget(civ);
+      if (budget < 0) {
+        const rate = this.getCentralBankRate(civ) / DAYS_PER_YEAR;
+        this.budgets.set(civ, budget * (1 + rate));
+      }
+      const demand = this._currencyDemand.get(civ) || 0;
+      const mass = this._currencyMass(civ);
+      const value = this.currencyValue(civ) * (1 + MONEY.demandSensitivity * (demand / mass));
+      this.setCurrencyValue(civ, value);
+      this._currencyDemand.set(civ, 0);
+    }
+  },
+
+  // A region uses any cash it has to pay down its central-bank debt, so the
+  // interest does not run away.
+  _repayRegionDebt(city, basket) {
+    const debt = this.regionDebt.get(city.id) || 0;
+    if (!(debt > 0)) return;
+    const code = this.currencyOf(city.civ).code;
+    const cash = basket.get(code) || 0;
+    const repay = Math.min(cash, debt);
+    if (!(repay > 0)) return;
+    basket.set(code, cash - repay);
+    this.regionDebt.set(city.id, debt - repay);
+  },
+
+  // A region turns a slice of every foreign currency it holds back into its own;
+  // the private sector prefers to carry national money. The conversion is priced
+  // through the global desk at today's rates.
+  _repatriateRegion(city, basket) {
+    const national = this.currencyOf(city.civ).code;
+    let changed = false;
+    for (const [code, amount] of Array.from(basket)) {
+      if (code === national || !(amount > 0)) continue;
+      const move = amount * MONEY.repatriationPerDay;
+      if (!(move > 0)) continue;
+      const value = move * this.currencyValueOf(code);
+      basket.set(code, amount - move);
+      const issuer = this._civByCurrencyCode().get(code);
+      if (issuer !== undefined) this._recordCurrencyDemand(issuer, -value);
+      this._recordCurrencyDemand(city.civ, value);
+      this._creditRegionCash(city, national, value / this.currencyValue(city.civ));
+      changed = true;
+    }
+    if (changed) this.regionCash.set(city.id, basket);
+  },
+
+  // ------------------------------------------------- serialization --
+
+  _serializeCurrencies() {
+    return this.civilisations.map((_, civ) => {
+      const currency = this.currencyOf(civ);
+      return {
+        civ,
+        code: currency.code,
+        symbol: currency.symbol,
+        name: currency.name,
+        value: this.currencyValue(civ),
+      };
+    });
+  },
+
+  // The exchange rate from the viewer's currency to every other nation's, for
+  // the national Economy tab.
+  _serializeExchangeRates(viewerCiv) {
+    return this.civilisations.map((_, civ) => {
+      const currency = this.currencyOf(civ);
+      return {
+        civ,
+        code: currency.code,
+        symbol: currency.symbol,
+        name: currency.name,
+        rate: this.exchangeRate(viewerCiv, civ),
+      };
+    });
+  },
+
+  _serializeCentralBank(civ) {
+    const reserves = [];
+    for (const [code, amount] of this.getCentralBankReserves(civ)) {
+      if (!(amount > 0)) continue;
+      const issuer = this._civByCurrencyCode().get(code);
+      const currency = issuer === undefined ? FALLBACK_CURRENCY : this.currencyOf(issuer);
+      reserves.push({ code, symbol: currency.symbol, name: currency.name, amount });
+    }
+    return {
+      rate: this.getCentralBankRate(civ),
+      currency: this.currencyOf(civ),
+      reserves,
+      // What the bank has lent: the government's overdraft plus region borrowing.
+      loans: this.getCentralBankLoans(civ),
+    };
+  },
+
+  _serializeRegionCash(city) {
+    const cash = {};
+    for (const [code, amount] of this.getRegionCash(city)) {
+      if (amount > 0) cash[code] = amount;
+    }
+    return cash;
+  },
+};
@@ -25,12 +25,15 @@ export const monthlyMethods = {
    // the same month a year earlier. A rolling 13 months is enough to always
    // hold the twelve-months-ago baseline.
    this._monthStartHistory = [{ index: this._monthIndexNow, stats: this._currentMonthStats }];
+    // The monthly budget report starts its first ledger here too.
+    this._initBudgetHistory();
  },

  // Called every hour; only a calendar-month change does any work.
  _tickMonthly() {
    const index = this._monthIndexOf(this.totalHours);
    if (index === this._monthIndexNow) return;
+    const previous = this._monthIndexNow;
    // What was current at the start of the month that just ended is now the
    // baseline for the new month.
    this.monthlyStats = this._currentMonthStats;
@@ -38,6 +41,8 @@ export const monthlyMethods = {
    this._monthIndexNow = index;
    this._monthStartHistory.push({ index, stats: this._currentMonthStats });
    if (this._monthStartHistory.length > 13) this._monthStartHistory.shift();
+    // The month that just ended becomes a browsable budget digest.
+    this._rolloverBudget(previous);
  },

  // The relative growth of a nation's headline figures against the same month a
@@ -7,6 +7,7 @@ import { GOVERNMENTS } from "../data/governments.js";
 import { PILLAGE, pillageSteps } from "../data/combat.js";
 import { transportImprovement } from "../data/improvements.js";
 import { buildingBuildCost, buildingRefund } from "../rules.js";
+import { tileImprovementResourceCost } from "../resources.js";
 import { TRAINING_QUEUE_LIMIT } from "./constants.js";

 export const orderMethods = {
@@ -39,7 +40,12 @@ export const orderMethods = {
    }
    const capacity = ECONOMY.productionCapacity(this.getPlayerGdp(city.civ));
    if (capacity <= 0) return false;
-    if (!this._spendBudget(city.civ, proto.cost)) return false;
+    if (!this._spendBudget(city.civ, proto.cost, "training")) return false;
+    const materials = this.constructionResourceCost(proto, 0, proto.cost);
+    if (!this._payConstructionResources(city.civ, city.coords, materials, "training")) {
+      this._refundBudget(city.civ, proto.cost, "training");
+      return false;
+    }
    const entry = {
      kind: "unit",
      protoIndex,
@@ -79,6 +85,7 @@ export const orderMethods = {
    // Placement rules: a port needs the sea, a shipyard needs a port.
    if (proto.coastal && !this.isCoastalCity(city)) return false;
    if (proto.requiresBuilding && !this.hasCityBuilding(city, proto.requiresBuilding)) return false;
+    if (proto.requiresTechnology && !this.hasTechnology(city.civ, proto.requiresTechnology)) return false;
    // The local testing shortcut: raise the next level at once, for free.
    if (free) {
      const level =
@@ -106,7 +113,12 @@ export const orderMethods = {
    }
    const capacity = ECONOMY.productionCapacity(this.getPlayerGdp(city.civ));
    if (capacity <= 0) return false;
-    if (!this._spendBudget(city.civ, cost)) return false;
+    if (!this._spendBudget(city.civ, cost, "construction")) return false;
+    const materials = this.constructionResourceCost(proto, level, cost);
+    if (!this._payConstructionResources(city.civ, city.coords, materials)) {
+      this._refundBudget(city.civ, cost, "construction");
+      return false;
+    }
    const entry = {
      kind: "building",
      protoIndex,
@@ -139,7 +151,14 @@ export const orderMethods = {
    if (this.civAt(coords) !== civ) return false;
    const current = this.railways.has(k) ? "railway" : this.roads.has(k) ? "road" : null;
    if (current === improvement.id) return false;
-    if (!free && !this._spendBudget(civ, improvement.buildCost)) return false;
+    if (!free) {
+      if (!this._spendBudget(civ, improvement.buildCost, "tilebuild")) return false;
+      const materials = tileImprovementResourceCost(improvement);
+      if (!this._payConstructionResources(civ, coords, materials, "tilebuild")) {
+        this._refundBudget(civ, improvement.buildCost, "tilebuild");
+        return false;
+      }
+    }
    this.roads.delete(k);
    this.railways.delete(k);
    if (improvement.id === "railway") this.railways.add(k);
@@ -177,7 +196,7 @@ export const orderMethods = {
    const level = this.getCityBuildingLevel(city, protoIndex);
    if (level <= 0) return false;
    const refund = buildingRefund(proto, level);
-    if (refund > 0) this.budgets.set(civ, this.getBudget(civ) + refund);
+    if (refund > 0) this._refundBudget(civ, refund, "construction");
    if (level <= 1) delete city.buildings[protoIndex];
    else city.buildings[protoIndex] = level - 1;
    this._gdpPerCapitaCache.clear();
@@ -192,8 +211,7 @@ export const orderMethods = {
    if (this.getGovernment(civ) === index) return false;
    const cost = GOVERNMENTS[index].baseCost +
      GOVERNMENTS[index].costGdpFraction * Math.max(this.getPlayerGdp(civ), 0);
-    if (cost > 0 && this.getBudget(civ) < cost) return false;
-    if (cost > 0) this.budgets.set(civ, this.getBudget(civ) - cost);
+    if (cost > 0) this._spendBudget(civ, cost, "campaign");
    this.government.set(civ, index);
    this._gdpPerCapitaCache.clear();
    this._touchModifiers();
@@ -232,8 +250,8 @@ export const orderMethods = {

  // Pillages the tile the units stand on. Every unit in the stack takes a turn,
  // the weakest first (least HP relative to maximum): each removes 10% of the
-  // remaining population, cuts the tile's GDP per capita by 30% and heals one
-  // hit point per 1000 people it drives off.
+  // remaining population, cuts the tile's production per head by 30% and heals
+  // one hit point per 1000 people it drives off.
  requestPillage(unitIds) {
    const units = this._unitsForOrder(unitIds);
    if (!this.canPillage(unitIds)) return false;
@@ -243,10 +261,12 @@ export const orderMethods = {
    const ordered = units.slice().sort((a, b) => a.hp / a.maxHp - b.hp / b.maxHp);
    let population = this.tilePopulation.get(k) || 0;
    const { steps } = pillageSteps(population, ordered.length);
-    let penalty = this.tileGdpPenalty.get(k) !== undefined ? this.tileGdpPenalty.get(k) : 1;
+    let penalty = this.tileProductionPenalty.get(k) !== undefined
+      ? this.tileProductionPenalty.get(k)
+      : 1;
    let drivenOff = 0;
    for (let i = 0; i < ordered.length; i++) {
-      penalty *= PILLAGE.gdpPenalty;
+      penalty *= PILLAGE.productionPenalty;
      const unit = ordered[i];
      unit.hp = Math.min(unit.maxHp, unit.hp + steps[i].heal);
      drivenOff += steps[i].removed;
@@ -254,7 +274,7 @@ export const orderMethods = {
    population = steps.length > 0 ? steps[steps.length - 1].remaining : population;
    this.tilePopulation.set(k, population);
    this._populationVersion += 1;
-    this.tileGdpPenalty.set(k, penalty);
+    this.tileProductionPenalty.set(k, penalty);
    this._gdpPerCapitaCache.delete(k);
    // The people driven off the tile are civilians lost to its owner in the war
    // against the pillaging civilisation.
@@ -61,6 +61,7 @@ export const politicsMethods = {
  _tickPolitics() {
    this._tickCampaigns();
    this._tickMigration();
+    this._migrateForIncome();
    this._tickUprisings();
    this._tickCultureImpact();
    this._expireGrudges();
@@ -672,6 +673,280 @@ export const politicsMethods = {
    this._migrateByAir();
  },

+  // ------------------------------------------------- income migration --
+
+  // People drift from poorer regions to richer ones, but only to places clearly
+  // richer: a destination must be at least `incomeRatioBase` times the source's
+  // income per head, and the bar rises the longer the journey takes. A flight
+  // crosses the distance in a flat few hours, but each airport can only move so
+  // many people a day.
+  _migrateForIncome() {
+    if (this.cities.length < 2) return;
+    const income = this._regionIncomePerCapita(this.cities);
+    // Each airport's daily intake, shared among every region that flies into it.
+    const airBudget = new Map();
+    for (const city of this.cities) {
+      const level = this._cityMechanicLevel(city, BUILDING_MECHANIC.AIR_IMMIGRATION);
+      if (level > 0) airBudget.set(city.id, MIGRATION.airPeoplePerDayPerLevel * level);
+    }
+    for (const from of this.cities) {
+      const fromIncome = income.get(from.id) || 0;
+      if (fromIncome <= 0) continue;
+      let source = this.regionPopulation(from) - MIGRATION.minRegionPopulation;
+      if (source <= 0) continue;
+      // The time bar only ever raises the requirement above the base ratio, so a
+      // region with no destination that much richer has nowhere to send anyone.
+      // Skip the route search entirely -- the common, balanced case.
+      const worthwhile = this.cities.some((other) =>
+        other !== from &&
+        (income.get(other.id) || 0) >= fromIncome * MIGRATION.incomeRatioBase
+      );
+      if (!worthwhile) continue;
+      const fromAirport = this._cityMechanicLevel(from, BUILDING_MECHANIC.AIR_IMMIGRATION);
+      const travel = this._migrationTravel(from);
+      for (const to of this.cities) {
+        if (to === from || source <= 0) continue;
+        const toIncome = income.get(to.id) || 0;
+        if (toIncome <= 0) continue;
+        // Two nations at war do not trade people.
+        if (this.isAtWar(from.civ, to.civ)) continue;
+        const toAirport = this._cityMechanicLevel(to, BUILDING_MECHANIC.AIR_IMMIGRATION);
+        const air = fromAirport > 0 && toAirport > 0;
+        const hours = air ? MIGRATION.airHours : travel.get(to.id);
+        if (hours === undefined) continue;
+        // The longer it takes, the richer the destination has to be.
+        const required = MIGRATION.incomeRatioBase * (1 + hours * MIGRATION.incomeTimePenalty);
+        const ratio = toIncome / fromIncome;
+        if (ratio < required) continue;
+        let amount;
+        if (air) {
+          const budget = airBudget.get(to.id) || 0;
+          amount = Math.min(budget, source);
+          if (amount <= 0) continue;
+          airBudget.set(to.id, budget - amount);
+        } else {
+          const rate = Math.min(
+            MIGRATION.incomeMaxSharePerDay,
+            MIGRATION.incomeSharePerDay * Math.min(ratio - required, MIGRATION.incomeGapCap)
+          );
+          amount = source * rate;
+        }
+        amount = Math.min(amount, source);
+        if (!(amount > 0)) continue;
+        this._movePopulation(from, to, amount);
+        source -= amount;
+      }
+    }
+  },
+
+  // The travel time in hours from one region to every city it can reach over the
+  // transport network, capped at `maxTravelHours`. Land is walked (roads and
+  // railways are faster), open water is crossed at the sea rate.
+  _migrationTravel(fromCity) {
+    // Travel times depend only on the transport network, so they are kept until
+    // a road, railway or port changes it.
+    if (!this._travelCache) this._travelCache = new Map();
+    const cached = this._travelCache.get(fromCity.id);
+    if (cached && cached.version === this._improvementVersion) return cached.result;
+    const hours = new Map();
+    const result = new Map();
+    const startKey = key(fromCity.coords.x, fromCity.coords.y);
+    hours.set(startKey, 0);
+    const queue = [fromCity.coords];
+    let head = 0;
+    while (head < queue.length) {
+      const coords = queue[head++];
+      const k = key(coords.x, coords.y);
+      const here = hours.get(k) || 0;
+      const city = this.cityAt(coords);
+      if (city && city !== fromCity) result.set(city.id, here);
+      if (here >= MIGRATION.maxTravelHours) continue;
+      for (const neighbour of this._neighbours(coords)) {
+        const nk = key(neighbour.x, neighbour.y);
+        if (hours.has(nk) || !this.tiles[nk]) continue;
+        const step = this._peopleHoursPerTile(neighbour);
+        if (!Number.isFinite(step)) continue;
+        hours.set(nk, here + step);
+        queue.push(neighbour);
+      }
+    }
+    this._travelCache.set(fromCity.id, { version: this._improvementVersion, result });
+    return result;
+  },
+
+  // What one tile costs a migrant in hours: open water is a flat sea rate, land
+  // is the terrain (or road/railway) multiplier over the walking speed.
+  _peopleHoursPerTile(coords) {
+    const tile = this.tiles[key(coords.x, coords.y)];
+    if (!tile) return Infinity;
+    if (tile.terrainClass === "Sea" || tile.terrainClass === "Ice") {
+      return MIGRATION.seaHoursPerTile;
+    }
+    return this._tileMovementMultiplier(coords, -1) / MIGRATION.peopleSpeed;
+  },
+
+  // The production per head of every region, as the economy shows it. The
+  // nation-wide balance is folded in here too, so two regions in different
+  // countries compare on the same footing.
+  _regionIncomePerCapita(cities) {
+    const result = new Map();
+    for (const city of cities) {
+      const economy = this.getCityEconomy(city);
+      result.set(city.id, economy.population > 0 ? economy.gdp / economy.population : 0);
+    }
+    return result;
+  },
+
+  // Moves `amount` people from one region to another, carrying their ethnic
+  // make-up with them. Source tiles lose people in proportion to what they hold
+  // and destination tiles gain the arrivals the same way, so a region's mix of
+  // terrain is preserved and only its density changes. Returns how many moved.
+  _movePopulation(fromCity, toCity, amount, record = true) {
+    if (!(amount > 0) || fromCity === toCity) return 0;
+    const source = this.regionTiles(fromCity)
+      .map((coords) => ({ coords, k: key(coords.x, coords.y) }))
+      .filter((entry) => (this.tilePopulation.get(entry.k) || 0) > 0);
+    const dest = this.regionTiles(toCity)
+      .map((coords) => ({ coords, k: key(coords.x, coords.y) }))
+      .filter((entry) => (this.tilePopulation.get(entry.k) || 0) > 0);
+    if (source.length === 0 || dest.length === 0) return 0;
+    const totalFrom = source.reduce((sum, entry) => sum + this.tilePopulation.get(entry.k), 0);
+    if (totalFrom <= 0) return 0;
+    const moved = Math.min(amount, totalFrom);
+    if (!(moved > 0)) return 0;
+
+    // The aggregate ethnic mix of the people leaving.
+    const mix = new Map();
+    for (const entry of source) {
+      const people = this.tilePopulation.get(entry.k) || 0;
+      const shares = this.tileEthnicity.get(entry.k);
+      if (!shares) continue;
+      for (const [eth, share] of shares) mix.set(eth, (mix.get(eth) || 0) + share * people);
+    }
+    const totalMix = Array.from(mix.values()).reduce((sum, value) => sum + value, 0) || 1;
+    for (const [eth, value] of mix) mix.set(eth, value / totalMix);
+
+    for (const entry of source) {
+      const people = this.tilePopulation.get(entry.k) || 0;
+      this.tilePopulation.set(entry.k, people - moved * people / totalFrom);
+    }
+    const totalTo = dest.reduce((sum, entry) => sum + this.tilePopulation.get(entry.k), 0);
+    for (const entry of dest) {
+      const people = this.tilePopulation.get(entry.k) || 0;
+      const add = totalTo > 0 ? moved * people / totalTo : moved / dest.length;
+      const after = people + add;
+      this.tilePopulation.set(entry.k, after);
+      const shares = new Map(this.tileEthnicity.get(entry.k) || []);
+      for (const [eth, share] of mix) {
+        const existing = shares.get(eth) || 0;
+        shares.set(eth, (existing * people + share * add) / after);
+      }
+      this._setTileEthnicFractions(parseKey(entry.k), shares);
+    }
+    this._populationVersion += 1;
+    this._gdpPerCapitaCache.clear();
+    // Keep each city's headline population in step with its city tile.
+    for (const city of [fromCity, toCity]) {
+      city.population = Math.round(
+        this.tilePopulation.get(key(city.coords.x, city.coords.y)) || 0
+      );
+    }
+    if (record) {
+      for (const [eth, share] of mix) {
+        const people = moved * share;
+        this._recordMigration(fromCity.civ, "out", eth, people);
+        this._recordMigration(toCity.civ, "in", eth, people);
+        this._trackMigration(
+          key(fromCity.coords.x, fromCity.coords.y),
+          key(toCity.coords.x, toCity.coords.y),
+          eth,
+          people
+        );
+      }
+    }
+    return moved;
+  },
+
+  // Start-of-game smoothing: within each nation, redistribute people so every
+  // region has the same production per head. A region's GDP does not depend on
+  // how many people live on its land -- food comes from the land and industry
+  // from its works -- so moving people in proportion leaves every region's GDP
+  // untouched and only changes the divisor. Equal income per head therefore
+  // means population proportional to GDP, which is one exact pass, no iteration.
+  _equalizeRegionIncomes() {
+    for (let civ = 0; civ < this.civilisations.length; civ++) {
+      const cities = this.cities.filter((city) => city.civ === civ);
+      if (cities.length < 2) continue;
+      // The population-proportional-to-GDP target is exact only while a region's
+      // GDP is independent of its people; flat per-head bonuses (ports, natural
+      // growth) make it depend a little, so a few passes settle it.
+      for (let pass = 0; pass < MIGRATION.equalizePasses; pass++) {
+        const population = new Map();
+        const gdp = new Map();
+        let totalPopulation = 0;
+        let totalGdp = 0;
+        let lowest = Infinity;
+        let highest = 0;
+        for (const city of cities) {
+          const people = this.regionPopulation(city);
+          const product = this.getCityEconomy(city).gdp;
+          population.set(city.id, people);
+          gdp.set(city.id, product);
+          totalPopulation += people;
+          totalGdp += product;
+          if (people > 0) {
+            const perHead = product / people;
+            if (perHead < lowest) lowest = perHead;
+            if (perHead > highest) highest = perHead;
+          }
+        }
+        if (totalGdp <= 0 || totalPopulation <= 0) break;
+        if (highest <= 0 || (highest - lowest) / highest <= MIGRATION.equalizeTolerance) {
+          break;
+        }
+        // The share of the nation's people each region should hold, with a floor
+        // so no region is emptied entirely.
+        let target = cities.map((city) => Math.max(
+          MIGRATION.minRegionPopulation,
+          totalPopulation * (gdp.get(city.id) || 0) / totalGdp
+        ));
+        const targetTotal = target.reduce((sum, value) => sum + value, 0);
+        if (targetTotal > totalPopulation) {
+          target = target.map((value) => value * totalPopulation / targetTotal);
+        }
+        const targetByCity = new Map(cities.map((city, index) => [city.id, target[index]]));
+        this._redistributePopulation(cities, population, targetByCity);
+      }
+    }
+    this._gdpPerCapitaCache.clear();
+  },
+
+  // Moves people from the regions holding more than their target to those
+  // holding less, so each ends at its target.
+  _redistributePopulation(cities, population, target) {
+    const surplus = [];
+    const deficit = [];
+    for (const city of cities) {
+      const delta = (population.get(city.id) || 0) - (target.get(city.id) || 0);
+      if (delta > 1) surplus.push({ city, amount: delta });
+      else if (delta < -1) deficit.push({ city, amount: -delta });
+    }
+    surplus.sort((a, b) => b.amount - a.amount);
+    deficit.sort((a, b) => b.amount - a.amount);
+    let index = 0;
+    for (const source of surplus) {
+      let remaining = source.amount;
+      while (remaining > 1 && index < deficit.length) {
+        const sink = deficit[index];
+        const moved = Math.min(remaining, sink.amount);
+        if (moved > 1) this._movePopulation(source.city, sink.city, moved, false);
+        remaining -= moved;
+        sink.amount -= moved;
+        if (sink.amount <= 1) index += 1;
+      }
+    }
+  },
+
  // People fly between airport cities. Every city with an airport draws a small
  // share of every other airport city's people, scaled by its own airport level,
  // so a busy hub grows at the expense of quieter ones. The move ignores
@@ -4,6 +4,7 @@
 import { parseKey } from "../hex.js";
 import { OPINION } from "../data/politics.js";
 import { EFFECT_RAIL_SPEED, EFFECT_CONSTRUCTION_SPEED, EFFECT_RESEARCH } from "../data/effects.js";
+import { RESOURCE_IDS } from "../data/resources.js";
 import { serializeSet } from "./helpers.js";

 export const serializationMethods = {
@@ -44,16 +45,19 @@ export const serializationMethods = {
      trenches: this._serializeTrenches(),
      tileImprovements: this._serializeTileImprovements(),
      // Each land tile's region: [x, y, cityId], so the browser attributes a
-      // tile's GDP modifiers to the city that develops it.
+      // tile's production modifiers to the city that develops it.
      regions: this._serializeRegions(),
      population: this._serializePopulation(),
-      // Every land tile's opening GDP per capita, the constant natural growth
-      // is measured from. Static, so it travels once and is then delta-dropped.
-      gdpBaseline: this._serializeGdpBaseline(),
+      // Every land tile's opening production per head, the constant natural
+      // growth is measured from. Static, so it travels once and is then dropped.
+      productionBaseline: this._serializeProductionBaseline(),
+      // The production per head each region starts from, before the tile
+      // modifiers. The browser mirrors the server's tile breakdown from it.
+      regionProductionBase: this._serializeRegionProductionBase(),
      // Sparse per-tile marks of war, so the browser can explain a tile's
-      // GDP per capita without shipping the whole breakdown for every tile.
-      tileGdpPenalties: this._serializeTileValues(this.tileGdpPenalty),
-      tileBattleGdpDeficits: this._serializeTileValues(this.tileBattleGdpDeficit),
+      // production per head without shipping the whole breakdown for every tile.
+      tileProductionPenalties: this._serializeTileValues(this.tileProductionPenalty),
+      tileBattleProductionDeficits: this._serializeTileValues(this.tileBattleProductionDeficit),
      civStats: this._serializeCivStats(),
      cityStats: cityStats,
      budgets: this._serializeCivValues(this.budgets),
@@ -87,6 +91,11 @@ export const serializationMethods = {
      conflicts: this._serializeConflicts(),
      news: this._serializeNews(),
      battles: this._serializeBattles(),
+      // The global resource market: today's price and the supply and demand
+      // that moved it, for the resource panel.
+      resourceMarket: this._serializeResourceMarket(),
+      // Every nation's imports and exports of each resource over the last day.
+      resourceTrade: this._serializeResourceTrade(),
      // Each nation's indicators a month ago, for the summary change arrows;
      // empty during January 2000, which has no past month.
      monthly: this.monthlyStats || [],
@@ -111,7 +120,8 @@ export const serializationMethods = {
        warfare: this._tileImprovementVersion,
        cityStats: hashCityStats(cityStats),
        visible: this._visibleVersion,
-        gdpBaseline: this._gdpBaselineVersion,
+        productionBaseline: this._productionBaselineVersion,
+        resourceGraph: this._resourceVersion,
      },
    };
  },
@@ -126,6 +136,9 @@ export const serializationMethods = {
    // an empty queue, so neither the map bar nor the city panel can reveal
    // whether a foreign city is busy.
    result.training = trainingForViewer(shared.training, shared.cities, viewerCiv);
+    // The delivery graph is the viewer's own network: its storage nodes and the
+    // legs that carried goods into its cities. Only the economic map reveals it.
+    result.resourceGraph = this._serializeResourceGraph(viewerCiv);
    return result;
  },

@@ -136,6 +149,7 @@ export const serializationMethods = {
        upkeep: 0, researchRate: 0, culture: 0, government: 0,
        approval: 0.5, popularity: 0, cultureImpact: 0, ethnicMakeup: [],
        constructionSpeed: 0, railSpeed: 0,
+        resources: null,
        breakdown: null,
      };
    }
@@ -146,8 +160,13 @@ export const serializationMethods = {
      // Repeatable research the browser mirrors: construction and rail speed.
      constructionSpeed: modifiers[EFFECT_CONSTRUCTION_SPEED] || 0,
      railSpeed: modifiers[EFFECT_RAIL_SPEED] || 0,
+      // The nation's stores, daily needs and production, plus today's prices.
+      resources: this.getCivResourceSummary(viewerCiv),
      budget: this.getBudget(viewerCiv),
-      upkeep: this.getPlayerUpkeep(viewerCiv),
+      // The upkeep figure the HUD nets against income: propaganda money plus
+      // the market value of the materials buildings, units and works wear out.
+      upkeep: this.getPlayerUpkeep(viewerCiv) +
+        this._upkeepCost(this.getCivUpkeepResources(viewerCiv)),
      // The research this nation creates each hour, all of which flows into the
      // focused technology. There is no stock of points.
      researchRate: modifiers[EFFECT_RESEARCH] || 0,
@@ -158,12 +177,42 @@ export const serializationMethods = {
      cultureImpact: this.getCulturalImpact(viewerCiv),
      ethnicMakeup: this.getCivEthnicMakeup(viewerCiv),
      breakdown: this.budgetBreakdown(viewerCiv),
+      // The month's budget, plus the last two years of monthly digests, so the
+      // panel can report what has actually been spent rather than a rate.
+      budgetMonths: this._serializeBudgetMonths(viewerCiv),
+      // Money: the nation's currency, everyone else's, the exchange rates the
+      // viewer sees, the central bank's rate and reserves, and the aggregate
+      // private-sector cash its regions hold.
+      currency: this.currencyOf(viewerCiv),
+      currencies: this._serializeCurrencies(),
+      exchangeRates: this._serializeExchangeRates(viewerCiv),
+      centralBank: this._serializeCentralBank(viewerCiv),
+      privateCash: this.getPrivateSectorCash(viewerCiv),
+      governmentDebt: this.getGovernmentDebt(viewerCiv),
      // How far the headline figures have grown, against January 2000 in the
      // first year and year-on-year afterwards.
      growth: this._growthRates(viewerCiv),
    };
  },

+  // The monthly budget reports, compacted for the wire: category ids replace
+  // the labels the client already knows from the data catalogue.
+  _serializeBudgetMonths(civ) {
+    return this.budgetMonthReports(civ).map((report) => ({
+      monthIndex: report.monthIndex,
+      isCurrent: report.isCurrent,
+      income: report.income,
+      sales: report.sales,
+      totalCash: report.totalCash,
+      totalEconomic: report.totalEconomic,
+      net: report.net,
+      expenses: report.expenses.map(
+        (entry) => [entry.id, entry.cash, entry.economic, entry.buys]
+      ),
+      resourceTrade: report.resourceTrade.map((entry) => [entry.id, entry.bought, entry.sold]),
+    }));
+  },
+
  _serializeCities() {
    return this.cities.map((city) => ({
      id: city.id,
@@ -207,6 +256,8 @@ export const serializationMethods = {
        airHours: unit.airHours,
        airborne: !!unit.airborne,
        homeCityId: unit.homeCityId,
+        // A land unit's carried food, in days. Zero means it is starving.
+        foodDays: unit.foodDays,
        // A standing bombardment target (ground battery) or bomb-run target
        // (aircraft), as [x, y], and the hour an aircraft may strike again.
        strikeTarget: unit.strikeTarget
@@ -298,22 +349,32 @@ export const serializationMethods = {
    return result;
  },

-  // A sparse [x, y, value] list of every land tile's opening GDP per capita. It
-  // never changes, so it is memoised and the delta wire drops it after the first
-  // snapshot a peer receives.
-  _serializeGdpBaseline() {
-    if (this._serializedGdpBaselineCache) return this._serializedGdpBaselineCache;
+  // A sparse [x, y, value] list of every land tile's opening production per
+  // head. It never changes, so it is memoised and the delta wire drops it after
+  // the first snapshot a peer receives.
+  _serializeProductionBaseline() {
+    if (this._serializedProductionBaselineCache) return this._serializedProductionBaselineCache;
    const result = [];
-    if (this.tileGdpBaseline) {
-      for (const [k, value] of this.tileGdpBaseline) {
+    if (this.tileProductionBaseline) {
+      for (const [k, value] of this.tileProductionBaseline) {
        const coords = parseKey(k);
        result.push([coords.x, coords.y, Math.round(value)]);
      }
    }
-    this._serializedGdpBaselineCache = result;
+    this._serializedProductionBaselineCache = result;
    return result;
  },

+  // Each region's production per head, before its tile modifiers, as
+  // [cityId, value]. Small and world-wide, so every viewer gets it and the tile
+  // panel can explain a tile's figure exactly as the server derived it.
+  _serializeRegionProductionBase() {
+    return this.cities.map((city) => [
+      city.id,
+      roundTo(this._regionProductionPerCapita(city), 4),
+    ]);
+  },
+
  // A sparse [x, y, value] list for a per-tile map, used for the war marks.
  _serializeTileValues(values) {
    const result = [];
@@ -353,6 +414,11 @@ export const serializationMethods = {
        income: economy.income,
        // The region's own income and building upkeep, for the city budget tab.
        budget: this.cityBudgetBreakdown(city, economy),
+        // The private-sector cash the region holds, a basket of currencies, and
+        // what it owes its central bank.
+        cash: this._serializeRegionCash(city),
+        cashValue: this.getRegionCashValue(city),
+        debt: this.getRegionDebt(city),
        // The ethnicity of the region's people, for the circle graph.
        ethnicMakeup: this.getCityEthnicMakeup(city),
      };
@@ -511,6 +577,65 @@ export const serializationMethods = {
    return civs.includes(owner) ? owner : civs[0];
  },

+  // -------------------------------------------------------- resources --
+
+  // Today's global price and the supply and demand behind it, one entry per
+  // resource. The figures are world-wide, so every viewer sees the same market.
+  _serializeResourceMarket() {
+    return RESOURCE_IDS.map((id) => {
+      const stats = this.resourceMarketStats ? this.resourceMarketStats.get(id) : null;
+      return {
+        id,
+        price: this.getResourcePrice(id),
+        supply: stats ? stats.supply : 0,
+        demand: stats ? stats.demand : 0,
+      };
+    });
+  },
+
+  // Every nation's imports and exports of each resource over the last day, so
+  // the Resources tab can show a viewer's own trade and rank the world's major
+  // exporters and importers. Cross-nation deliveries only.
+  _serializeResourceTrade() {
+    return this.civilisations.map((_, civ) => {
+      const record = this.resourceTrade ? this.resourceTrade.get(civ) : null;
+      const imports = {};
+      const exports = {};
+      for (const id of RESOURCE_IDS) {
+        imports[id] = roundTo(record ? record.imports[id] || 0 : 0, 3);
+        exports[id] = roundTo(record ? record.exports[id] || 0 : 0, 3);
+      }
+      return { civ, imports, exports };
+    });
+  },
+
+  // The viewer's own storage nodes and delivery legs, as [x, y] nodes and
+  // [fromX, fromY, toX, toY, resource, amount] links. A spectator sees none.
+  _serializeResourceGraph(viewerCiv) {
+    if (viewerCiv < 0 || !this.resourceStock) return { nodes: [], links: [] };
+    const nodes = [];
+    for (const [k] of this.resourceStock) {
+      const coords = parseKey(k);
+      const node = this._resourceNodeAt(coords);
+      if (!node || node.civ !== viewerCiv) continue;
+      nodes.push([coords.x, coords.y, node.kind === "city" ? 1 : 0]);
+    }
+    const links = [];
+    for (const link of this.resourceLinks || []) {
+      const to = link.to;
+      if (this.civAt({ x: to[0], y: to[1] }) !== viewerCiv) continue;
+      links.push([
+        link.from[0],
+        link.from[1],
+        link.to[0],
+        link.to[1],
+        link.resource,
+        Math.round(link.amount * 1000) / 1000,
+      ]);
+    }
+    return { nodes, links };
+  },
+
  // --------------------------------------------------------- politics --

  // Every nation's share of world culture, as a fraction per civilisation.
@@ -1,33 +1,26 @@
-// Supply: encirclement and siege detection, including the maritime exception
-// that keeps a coastal city supplied through allied naval units.
+// Supply: encirclement and siege detection. A tile is cut off when enemy units
+// sit on every land tile beside it and it has no working port to bring supplies
+// in by sea; a port is itself blockaded when enemy warships hold every sea tile
+// around its city.

 import { key } from "../hex.js";
 import { STATUS_ENCIRCLED, STATUS_BESIEGED } from "../data/statuses.js";

 export const statusMethods = {
-  // Recomputes the status of every unit and city. The supply search only runs
-  // for an occupant that has a hostile unit adjacent, and only once a day (and
-  // at setup), so it never touches the snapshot path.
+  // Recomputes the status of every unit and city. A unit cut off is encircled;
+  // a city cut off is besieged. The check is local -- the ring of land tiles
+  // around the occupant and its own port -- so it never walks the whole map.
  _refreshStatuses() {
-    const components = new Map();
    for (const unit of this.units) {
-      if (!this._hasAdjacentHostile(unit.coords, unit.civ)) {
-        unit.statuses = [];
-        continue;
-      }
-      unit.statuses = this._unitStatuses(unit, this._componentsFor(components, unit.civ));
+      unit.statuses = this._isEncircled(unit.coords, unit.civ) ? [STATUS_ENCIRCLED] : [];
    }
    for (const city of this.cities) {
-      if (!this._hasAdjacentHostile(city.coords, city.civ)) {
-        city.statuses = [];
-        continue;
-      }
-      city.statuses = this._cityStatuses(city, this._componentsFor(components, city.civ));
+      city.statuses = this._isEncircled(city.coords, city.civ) ? [STATUS_BESIEGED] : [];
    }
  },

-  // The trigger: encirclement is only evaluated when a hostile unit is next to
-  // the tile.
+  // Whether a hostile unit stands next to `coords`. Kept as the cheap trigger
+  // for callers that only care whether a fight is near.
  _hasAdjacentHostile(coords, civ) {
    for (const neighbour of this._neighbours(coords)) {
      if (this.unitsAt(neighbour).some((unit) => unit.civ !== civ)) return true;
@@ -35,20 +28,60 @@ export const statusMethods = {
    return false;
  },

-  _componentsFor(cache, civ) {
-    if (!cache.has(civ)) cache.set(civ, this._landComponents(civ));
-    return cache.get(civ);
+  // A tile is encircled when no enemy warship can break the ring: it has no
+  // working port, and every land tile beside it is held by an enemy unit. A
+  // tile with no land neighbours has no ring to close, so it is not encircled.
+  _isEncircled(coords, civ) {
+    if (this._hasSeaSupply(coords, civ)) return false;
+    return this._landRingBlocked(coords, civ);
+  },
+
+  _landRingBlocked(coords, civ) {
+    let land = 0;
+    for (const neighbour of this._neighbours(coords)) {
+      const tile = this.tiles[key(neighbour.x, neighbour.y)];
+      if (!tile || tile.terrainClass !== "Land") continue;
+      land += 1;
+      if (!this.unitsAt(neighbour).some((unit) => unit.civ !== civ)) return false;
+    }
+    return land > 0;
+  },
+
+  // A friendly city's port supplies its own tile by sea, unless the port is
+  // blockaded.
+  _hasSeaSupply(coords, civ) {
+    const city = this.cityAt(coords);
+    if (!city || city.civ !== civ) return false;
+    if (!this.hasCityBuilding(city, "port")) return false;
+    return !this._isPortBlockaded(city);
+  },
+
+  // A port is blockaded when enemy warships hold every sea tile around the city.
+  _isPortBlockaded(city) {
+    let sea = 0;
+    let held = 0;
+    for (const neighbour of this._neighbours(city.coords)) {
+      const tile = this.tiles[key(neighbour.x, neighbour.y)];
+      if (!tile || tile.terrainClass !== "Sea") continue;
+      sea += 1;
+      if (this.unitsAt(neighbour).some(
+        (unit) => unit.civ !== city.civ && this._isNaval(unit))) {
+        held += 1;
+      }
+    }
+    return sea > 0 && held === sea;
  },

  _isNaval(unit) {
    const proto = this.unitProto(unit);
    // Aircraft may fly over the sea, but only a hull counts as naval supply.
-    return !!(proto && !proto.air && proto.traversableTerrains.includes("Sea"));
+    return !!(proto && !proto.air && (proto.traversableTerrains || []).includes("Sea"));
  },

  // Land connected components for one civ, with enemy-occupied and enemy-held
  // city tiles acting as walls. Each component remembers how many of the civ's
-  // cities it contains, which is all the supply check needs.
+  // cities it contains. Used by the unit supply rule to find a clear route to
+  // an allied city.
  _landComponents(civ) {
    const byTile = new Map();
    const cityCountByComp = new Map();
@@ -89,76 +122,6 @@ export const statusMethods = {
    return true;
  },

-  // A city is besieged when it no longer shares a land component with any
-  // other city of its civ. A lone city is never besieged.
-  _isCityBesieged(city, info) {
-    if (info.totalCities < 2) return false;
-    const component = info.byTile.get(key(city.coords.x, city.coords.y));
-    const count = component === undefined ? 0 : (info.cityCountByComp.get(component) || 0);
-    return count <= 1;
-  },
-
-  _unitStatuses(unit, info) {
-    const city = this.cityAt(unit.coords);
-    const inOwnCity = city && city.civ === unit.civ;
-    let encircled;
-    if (inOwnCity) {
-      encircled = this._isCityBesieged(city, info);
-    } else {
-      const component = info.byTile.get(key(unit.coords.x, unit.coords.y));
-      const count = component === undefined ? 0 : (info.cityCountByComp.get(component) || 0);
-      encircled = count === 0;
-    }
-    const excludeCity = inOwnCity ? city.id : 0;
-    if (encircled && this._hasMaritimeRoute(unit.coords, unit.civ, excludeCity)) {
-      encircled = false;
-    }
-    return encircled ? [STATUS_ENCIRCLED] : [];
-  },
-
-  _cityStatuses(city, info) {
-    const besieged = this._isCityBesieged(city, info) &&
-      !this._hasMaritimeRoute(city.coords, city.civ, city.id);
-    return besieged ? [STATUS_BESIEGED] : [];
-  },
-
-  // The maritime exception: with an allied naval unit on an adjacent sea tile,
-  // a lane is traced across water to a different coastal allied city. Enemy
-  // units on the water block it.
-  _hasMaritimeRoute(origin, civ, excludeCityId) {
-    const visited = new Set();
-    let frontier = [];
-    for (const neighbour of this._neighbours(origin)) {
-      const tile = this.tiles[key(neighbour.x, neighbour.y)];
-      if (!tile || tile.terrainClass !== "Sea") continue;
-      if (!this.unitsAt(neighbour).some((unit) => unit.civ === civ && this._isNaval(unit))) continue;
-      const nk = key(neighbour.x, neighbour.y);
-      if (visited.has(nk)) continue;
-      visited.add(nk);
-      frontier.push(neighbour);
-    }
-    while (frontier.length > 0) {
-      const next = [];
-      for (const coords of frontier) {
-        for (const neighbour of this._neighbours(coords)) {
-          const city = this.cityAt(neighbour);
-          if (city && city.civ === civ && city.id !== excludeCityId) return true;
-        }
-        for (const neighbour of this._neighbours(coords)) {
-          const tile = this.tiles[key(neighbour.x, neighbour.y)];
-          if (!tile || tile.terrainClass !== "Sea") continue;
-          const nk = key(neighbour.x, neighbour.y);
-          if (visited.has(nk)) continue;
-          if (this.unitsAt(neighbour).some((unit) => unit.civ !== civ)) continue;
-          visited.add(nk);
-          next.push(neighbour);
-        }
-      }
-      frontier = next;
-    }
-    return false;
-  },
-
  _statusHpLossPerDay(def, inCity) {
    if (inCity && typeof def.cityHpLossPerDay === "number") return def.cityHpLossPerDay;
    return typeof def.hpLossPerDay === "number" ? def.hpLossPerDay : 0;
@@ -7,12 +7,13 @@ import { ECONOMY } from "../data/economy.js";
 import { TRANSPORT_BY_ID, tileImprovementById } from "../data/improvements.js";
 import { TRENCH } from "../data/combat.js";
 import { TILE_IMPROVEMENT_HP, COASTAL_CANNON, EMBARK_HOURS } from "./constants.js";
+import { protoUpkeep, tileImprovementResourceCost } from "../resources.js";

 export const warfareMethods = {
  // ----------------------------------------------------------- trenches --

  // Infantry dig in on a land tile their nation controls. A trench shelters
-  // the garrison from melee and artillery at the cost of local GDP.
+  // the garrison from melee and artillery at the cost of local production.
  requestDigTrench(unitIds) {
    const units = this._unitsForOrder(unitIds);
    if (units.length === 0) return false;
@@ -54,9 +55,17 @@ export const warfareMethods = {
    if (this.civAt(coords) !== civ) return false;
    if (this.tileImprovements.has(k)) return false;
    if (proto.coastal && !this._isCoastalTile(coords)) return false;
+    // Resource producers feed the map, not a city: they stand on open land.
+    if (proto.resource && this.cityAt(coords)) return false;
+    if (proto.requiresTechnology && !this.hasTechnology(civ, proto.requiresTechnology)) return false;
    const gdp = this.getPlayerGdp(civ);
    if (ECONOMY.productionCapacity(gdp) <= 0) return false;
-    if (!this._spendBudget(civ, proto.buildCost)) return false;
+    if (!this._spendBudget(civ, proto.buildCost, "tilebuild")) return false;
+    const materials = tileImprovementResourceCost(proto, proto.buildCost);
+    if (!this._payConstructionResources(civ, coords, materials, "tilebuild")) {
+      this._refundBudget(civ, proto.buildCost, "tilebuild");
+      return false;
+    }
    const work = {
      coords: { x: coords.x, y: coords.y },
      id,
@@ -189,6 +198,8 @@ export const warfareMethods = {
      return true;
    }
    this.tileImprovementHp.set(k, hp);
+    // The damage leaves a steel debt: the work heals only once it is paid off.
+    this._recordRepairDebt(coords, amount);
    return true;
  },

@@ -207,13 +218,14 @@ export const warfareMethods = {
    return true;
  },

-  // The hourly maintenance of every military improvement a nation holds.
+  // The daily steel every military and resource improvement a nation holds
+  // wears out. Fuel and operating energy are charged through the grid instead.
  getTileImprovementUpkeep(civ) {
    let total = 0;
    for (const [k, id] of this.tileImprovements) {
      if (this.tileImprovementOwner.get(k) !== civ) continue;
      const proto = tileImprovementById(id);
-      if (proto) total += proto.maintenance;
+      if (proto) total += protoUpkeep(proto, proto.buildCost || 0).steel;
    }
    return total;
  },
@@ -224,12 +236,23 @@ export const warfareMethods = {
      if (this.tileImprovementOwner.get(k) !== civ) continue;
      const proto = tileImprovementById(id);
      if (!proto) continue;
-      const entry = byType.get(id) || { label: proto.name, amount: 0, count: 0 };
-      entry.amount += proto.maintenance;
+      const resources = protoUpkeep(proto, proto.buildCost || 0);
+      const amount = this._upkeepCost(resources);
+      if (amount <= 0) continue;
+      const entry = byType.get(id) || {
+        label: proto.name,
+        amount: 0,
+        resources: { steel: 0, energy: 0, hightech: 0 },
+        count: 0,
+      };
+      entry.amount += amount;
+      entry.resources.steel += resources.steel;
+      entry.resources.energy += resources.energy;
+      entry.resources.hightech += resources.hightech;
      entry.count += 1;
      byType.set(id, entry);
    }
-    return Array.from(byType.values()).filter((entry) => entry.amount > 0);
+    return Array.from(byType.values());
  },

  // ------------------------------------------------------ transports --
@@ -3,6 +3,7 @@
 // terrain predicates the rest of the model leans on.

 import { ECONOMY } from "../data/economy.js";
+import { RESOURCE_RULES } from "../data/resources.js";
 import { ROADS } from "../data/roads.js";
 import { transportImprovement } from "../data/improvements.js";
 import { buildRoadNetwork } from "../roads.js";
@@ -82,6 +83,7 @@ export const worldMethods = {
      : this._placeCities(capitals);
    for (const site of sites) this._spawnCity(site);
    this._rebuildCityIndex();
+    this._seedCityPorts();
    this._generateRoads(cached ? cached.roads : null);
    if (!cached) {
      cachePut(settlementCache, cacheKey, {
@@ -98,6 +100,18 @@ export const worldMethods = {
    this._initPolitics();
    this._generateEthnicMakeup();
    this._balanceStartingEconomy();
+    // Every nation opens with the resource works its economy needs, laid out
+    // before the budgets are founded so the opening treasury already reflects
+    // them.
+    this._seedResourceBuildings();
+    // The terrain and where the starter industry landed give each region a
+    // different income per head. Unworked land is not what makes a region rich
+    // (food comes from the land, not the headcount), so people now move out of
+    // the poor regions until every region of a nation is level.
+    this._equalizeRegionIncomes();
+    // The starter industry lifts raw GDP unevenly; restore the equal starting
+    // production per head without disturbing the grid demand the seeding planned.
+    this._rebalanceProduction();
    // Budgets are founded once the balanced economy is known, so every nation
    // opens on 1 January 2000 with a tenth of its own starting GDP.
    this._initBudgets();
@@ -151,6 +165,17 @@ export const worldMethods = {
    }
  },

+  // Every naval city opens the game with a port. It is the only way a nation can
+  // reach resources on other continents, so a coastal city is never landlocked
+  // in trade from the first turn.
+  _seedCityPorts() {
+    const index = this.protoBuildings.findIndex((proto) => proto.id === "port");
+    if (index < 0) return;
+    for (const city of this.cities) {
+      if (this.isCoastalCity(city)) city.buildings[index] = 1;
+    }
+  },
+
  // Picks the civilisation's next city name, skipping any a city elsewhere has
  // already taken, and falls back to a numbered name so the whole world never
  // has two cities called the same thing.
@@ -221,6 +246,9 @@ export const worldMethods = {
      // A transport's cargo and any boarding under way.
      cargo: [],
      embarking: null,
+      // A land unit's carried food, in days. Air and naval units use their own
+      // endurance models instead.
+      foodDays: RESOURCE_RULES.unitSupplyDays,
    };
    if (proto.air) {
      unit.homeCityId = homeCityId;
@@ -257,13 +285,13 @@ export const worldMethods = {
  // Map generation should not hand one civilisation a richer start than
  // another. Terrain makes the raw territories unequal, so after the world is
  // populated we scale each civ's population to the common mean and then its
-  // GDP per capita to the mean of the raw per-capita figures. Total population
+  // production per head to the mean of the raw figures. Total population
  // and total GDP are preserved; from here on the factors are constants and
  // terrain, buildings, technology and war move the numbers normally.
  _balanceStartingEconomy() {
    const count = this.civilisations.length;
    this._populationBalance = new Map();
-    this._perCapitaBalance = new Map();
+    this._productionBalance = new Map();
    if (count <= 1) return;
    const bases = [];
    let totalPopulation = 0;
@@ -276,16 +304,36 @@ export const worldMethods = {
    }
    if (totalPopulation <= 0) return;
    const targetPopulation = totalPopulation / count;
-    const targetPerCapita = totalGdp / totalPopulation;
+    const targetPerHead = totalGdp / totalPopulation;
+    // Kept so the production balance can be restored once the starter industry
+    // has been laid out and the raw figures have moved.
+    this._targetProductionPerHead = targetPerHead;
    for (let i = 0; i < count; i++) {
      const base = bases[i];
      if (base.population <= 0) continue;
-      const perCapita = base.gdp / base.population;
+      const perHead = base.gdp / base.population;
      this._populationBalance.set(i, targetPopulation / base.population);
-      this._perCapitaBalance.set(i, perCapita > 0 ? targetPerCapita / perCapita : 1);
+      this._productionBalance.set(i, perHead > 0 ? targetPerHead / perHead : 1);
    }
  },

+  // Seeding the starter resource works changes every nation's raw GDP, but the
+  // production balance must still hold: nations should not open richer just
+  // because their land happens to host more industry. Re-derive the production
+  // factor from the post-seeding figures against the same target, which also
+  // leaves each nation's balanced GDP (and so its grid demand) exactly where
+  // the seeding planned it.
+  _rebalanceProduction() {
+    if (!(this._targetProductionPerHead > 0)) return;
+    for (let i = 0; i < this.civilisations.length; i++) {
+      const base = this._basePlayerAggregates(i);
+      if (base.population <= 0) continue;
+      const perHead = base.gdp / base.population;
+      this._productionBalance.set(i, perHead > 0 ? this._targetProductionPerHead / perHead : 1);
+    }
+    this._gdpPerCapitaCache.clear();
+  },
+
  _isLand(coords) {
    const tile = this.tiles[key(coords.x, coords.y)];
    return !!tile && tile.terrainClass === "Land";
@@ -0,0 +1,225 @@
+// Pure resource maths shared by the server (which simulates the economy) and
+// the browser (which explains it). Everything here is framework-free and takes
+// plain numbers, so both sides derive identical figures from the same rules in
+// shared/data/resources.js.
+
+import {
+  RESOURCE_IDS,
+  RESOURCE_RULES,
+  RESOURCE_MARKET,
+  RESOURCE_MARKET_BASE,
+  resourceById,
+} from "./data/resources.js";
+import { EFFECT_RESEARCH } from "./data/effects.js";
+
+const DAYS_PER_YEAR = 365;
+
+// --------------------------------------------------------------- formatting --
+
+// Energy reads in kWh, MWh, GWh or TWh, whichever keeps the figure short.
+export function formatEnergy(kwh) {
+  const value = Math.max(0, kwh);
+  if (value >= 1e9) return `${trim(value / 1e9)} TWh`;
+  if (value >= 1e6) return `${trim(value / 1e6)} GWh`;
+  if (value >= 1e3) return `${trim(value / 1e3)} MWh`;
+  return `${trim(value)} kWh`;
+}
+
+// A material in its own friendly unit: tonnes step up through kt and Mt,
+// carats through kct, high-tech through ku.
+export function formatResourceAmount(id, value) {
+  if (id === "energy") return formatEnergy(value);
+  const amount = Math.max(0, value);
+  let unit = resourceById(id) ? resourceById(id).unit : "";
+  let scaled = amount;
+  let prefix = "";
+  if (amount >= 1e9) {
+    scaled = amount / 1e9;
+    prefix = "M";
+  } else if (amount >= 1e6) {
+    scaled = amount / 1e6;
+    prefix = "k";
+  }
+  return `${trim(scaled)} ${prefix}${unit}`;
+}
+
+function trim(value) {
+  if (value >= 100) return String(Math.round(value));
+  if (value >= 10) return value.toFixed(1).replace(/\.0$/, "");
+  return value.toFixed(2).replace(/\.?0+$/, "");
+}
+
+// --------------------------------------------------------------- per-person --
+
+export function foodNeedPerDay(population) {
+  return Math.max(0, population) * RESOURCE_RULES.foodPerPersonPerDay;
+}
+
+export function steelNeedPerDay(population) {
+  return Math.max(0, population) * RESOURCE_RULES.steelPerPersonPerDay;
+}
+
+export function luxuryNeedPerDay(population) {
+  return Math.max(0, population) * RESOURCE_RULES.luxuryPerPersonPerDay;
+}
+
+// What one worked land tile grows in a day. Food comes from the land, not from
+// how many people live on it: a farm feeds whoever works it, so moving people
+// between regions changes only the income per head, never the harvest. A tile
+// feeds roughly `ECONOMY.basePopulation` people at factor 1.
+export function tileFoodOutput(tile) {
+  const factor = RESOURCE_RULES.tileFoodFactor[tile.terrainType] ?? 1;
+  return RESOURCE_RULES.foodPerTilePerDay * factor;
+}
+
+// How much food a city wants in store before the coming month: a month at the
+// current appetite, with a 130% cushion.
+export function foodMonthlyTarget(population) {
+  return foodNeedPerDay(population) *
+    RESOURCE_RULES.daysPerMonth *
+    RESOURCE_RULES.foodMonthlyBuffer;
+}
+
+// A city's baseline electric appetite, kWh a day, from its yearly GDP.
+export function cityEnergyPerDay(gdp) {
+  return Math.max(0, gdp) * RESOURCE_RULES.gdpEnergyIntensity / DAYS_PER_YEAR;
+}
+
+// What one building level, unit or tile work wears out in a day, from its money
+// value. Advanced things also burn high-tech. Buildings pass their level's cost
+// (so upkeep grows with the level), units their training cost.
+export function upkeepResources(value, advanced = false) {
+  const amount = Math.max(0, value);
+  return {
+    steel: amount * RESOURCE_RULES.upkeepSteelPerEuro,
+    energy: amount * RESOURCE_RULES.upkeepEnergyPerEuro,
+    hightech: advanced ? amount * RESOURCE_RULES.upkeepHighTechPerEuro : 0,
+  };
+}
+
+// The daily upkeep of a catalogue entry. An explicit `materialUpkeep` override
+// wins -- guns and aircraft are cheap parked and costly when fired, so their
+// standing bill is set by hand -- otherwise it scales with the entry's value.
+export function protoUpkeep(proto, value) {
+  if (proto && proto.materialUpkeep) {
+    return {
+      steel: proto.materialUpkeep.steel || 0,
+      energy: proto.materialUpkeep.energy || 0,
+      hightech: proto.materialUpkeep.hightech || 0,
+    };
+  }
+  return upkeepResources(value, !!(proto && proto.advanced));
+}
+
+// The materials and power a tile improvement spends to be built: steel in
+// proportion to its money cost, the electricity that steel embodies, and
+// high-tech for an advanced work. Shared so the server's bill and the browser's
+// cost buttons agree on the same figures.
+export function tileImprovementResourceCost(proto, buildCost = null) {
+  const cost = Math.max(0, buildCost !== null ? buildCost : ((proto && proto.buildCost) || 0));
+  return {
+    steel: cost * RESOURCE_RULES.steelPerBudgetEuro,
+    energy: cost * RESOURCE_RULES.constructionEnergyPerBudgetEuro,
+    hightech: proto && proto.advanced ? RESOURCE_RULES.constructionHighTechPerLevel : 0,
+  };
+}
+
+// The steel and high-tech a building or unit spends to be built: steel in
+// proportion to its money cost, high-tech for an advanced item (more with every
+// level). Mirrors the server's construction bill so the browser can quote it at
+// today's prices.
+export function constructionResourceCost(proto, level = 0, buildCost = null) {
+  const cost = buildCost !== null ? buildCost : ((proto && (proto.buildCost || proto.baseCost)) || 0);
+  const advanced = !!(proto && (proto.advanced ||
+    (proto.effects || []).some((e) => e.stat === EFFECT_RESEARCH)));
+  return {
+    steel: Math.max(0, cost) * RESOURCE_RULES.steelPerBudgetEuro,
+    hightech: advanced ? RESOURCE_RULES.constructionHighTechPerLevel * (level + 1) : 0,
+  };
+}
+
+// Today's global price index: the average ratio of each resource's current
+// price to its base. One figure lets a money cost with no material bill of its
+// own be quoted at the market.
+export function marketPriceIndex(prices) {
+  let total = 0;
+  let count = 0;
+  for (const id of RESOURCE_IDS) {
+    const base = RESOURCE_MARKET_BASE[id];
+    if (!(base > 0)) continue;
+    const price = prices && prices[id] !== undefined ? prices[id] : base;
+    total += price / base;
+    count += 1;
+  }
+  return count > 0 ? total / count : 1;
+}
+
+// The market value of a resource bill at the given prices, a resource at a time.
+export function resourceMarketValue(resources, prices) {
+  let total = 0;
+  for (const id of RESOURCE_IDS) {
+    const amount = (resources && resources[id]) || 0;
+    if (!(amount > 0)) continue;
+    const price = prices && prices[id] !== undefined ? prices[id] : RESOURCE_MARKET_BASE[id];
+    total += amount * (price || 0);
+  }
+  return total;
+}
+
+// The energy a material producer burns to make its output: the energy-per-unit
+// ratio from the rules, whichever resource it makes.
+export function producerEnergyPerDay(id, outputPerDay) {
+  if (id === "steel") return outputPerDay * RESOURCE_RULES.energyPerSteelTonne;
+  if (id === "food") return outputPerDay * RESOURCE_RULES.energyPerFoodTonne;
+  if (id === "hightech") return outputPerDay * RESOURCE_RULES.energyPerHighTechUnit;
+  return 0;
+}
+
+// ---------------------------------------------------------------- delivery --
+
+// The kWh of transport energy one material tonne costs over `tiles` tiles in the
+// given mode. A material tonne and an energy tonne (10 GWh) share the formula.
+export function deliveryEnergyKwh(tonnes, tiles, mode, tileMovementCost = 1) {
+  const d = RESOURCE_RULES.deliveryEnergy;
+  const perTile = mode === "train"
+    ? d.train
+    : mode === "ship"
+      ? d.ship
+      : mode === "road"
+        ? d.truckRoad
+        : d.truckOffRoad * Math.max(tileMovementCost, 0);
+  return tonnes * Math.max(tiles, 0) * perTile;
+}
+
+// The energy cost of delivering `amount` of a resource over `tiles`. Every
+// resource carries a mass per canonical unit, so a carat or a chip is charged
+// for the tonnes it actually weighs rather than as if it were a tonne.
+export function deliveryEnergyForResource(id, amount, tiles, mode, tileMovementCost = 1) {
+  const proto = resourceById(id);
+  const tonnes = amount * (proto ? proto.tonnesPerUnit : 1);
+  return deliveryEnergyKwh(tonnes, tiles, mode, tileMovementCost);
+}
+
+// The transport mode a tile offers, most efficient first: rail beats road, and
+// an unimproved tile falls back to an off-road truck. Sea legs ship.
+export function transportModeForTile(tile, road, railway, sea) {
+  if (sea || (tile && tile.terrainClass === "Sea")) return "ship";
+  if (railway) return "train";
+  if (road) return "road";
+  return "truck";
+}
+
+// ----------------------------------------------------------------- market --
+
+// Moves a price toward what the day's world-wide supply and demand imply. A
+// glut pushes it down, a shortage up, and the clamp keeps the market sane. A
+// zero-supply day is treated as the sharpest shortage.
+export function nextMarketPrice(basePrice, price, supply, demand) {
+  if (!(demand > 0)) return basePrice;
+  const ratio = supply > 0 ? demand / supply : RESOURCE_MARKET.maxMultiplier;
+  const pressure = (ratio - 1) * RESOURCE_MARKET.adjustment;
+  const moved = price * (1 + pressure);
+  const min = basePrice * RESOURCE_MARKET.minMultiplier;
+  const max = basePrice * RESOURCE_MARKET.maxMultiplier;
+  return Math.max(min, Math.min(max, moved));
+}
@@ -107,13 +107,13 @@ export function unitDefense(baseDefense, tile, hasCity) {
  return baseDefense * defenseMultiplier(tile, hasCity);
 }

-// Every GDP-per-capita modifier of a tile, in display order. `tile` supplies the
+// Every production modifier of a tile, in display order. `tile` supplies the
 // terrain multiplier and its name; `cityKind` is "capital", "city" or null and
 // `nextToCity` is true when the tile borders one of its owner's cities. The
 // pillage penalty and battle deficit are the lasting marks of war. Shared by the
-// server (which derives each tile's GDP) and the browser (which explains it), so
-// the numbers always agree.
-export function gdpPerCapitaFactors(tile, {
+// server (which derives each tile's production) and the browser (which explains
+// it), so the numbers always agree.
+export function productionFactors(tile, {
  cityKind = null,
  nextToCity = false,
  pillagePenalty = 1,
@@ -122,28 +122,28 @@ export function gdpPerCapitaFactors(tile, {
  regionalMultiplier = 1,
  regionalLabel = null,
  nationalMultiplier = 1,
-  portGdp = 0,
+  portProduction = 0,
  naturalGrowth = 0,
 } = {}) {
  const factors = [];
-  const terrainMultiplier = tile ? tile.gdpMultiplier || 0 : 0;
+  const terrainMultiplier = tile ? tile.productionMultiplier || 0 : 0;
  factors.push({ label: tile ? tile.terrainType : "Unknown", multiplier: terrainMultiplier });
  if (cityKind === "capital") {
-    factors.push({ label: "Capital", multiplier: ECONOMY.capitalTileGdpMultiplier });
+    factors.push({ label: "Capital", multiplier: ECONOMY.capitalTileProductionMultiplier });
  } else if (cityKind === "city") {
-    factors.push({ label: "City", multiplier: ECONOMY.cityTileGdpMultiplier });
+    factors.push({ label: "City", multiplier: ECONOMY.cityTileProductionMultiplier });
  } else if (nextToCity) {
-    factors.push({ label: "Near city", multiplier: 1 + ECONOMY.citySurroundingGdpBonus });
+    factors.push({ label: "Near city", multiplier: 1 + ECONOMY.citySurroundingProductionBonus });
  }
  if (pillagePenalty !== 1) {
    factors.push({ label: "Pillaging", multiplier: pillagePenalty });
  }
  if (trench) {
-    factors.push({ label: "Trenches", multiplier: TRENCH.gdpMultiplier });
+    factors.push({ label: "Trenches", multiplier: TRENCH.productionMultiplier });
  }
  // City improvements only shape the region their city controls, so a tile's
-  // GDP per capita carries its region's multiplier plus the nation-wide one
-  // from government and research. Both are factors on the per-capita figure,
+  // production carries its region's multiplier plus the nation-wide one
+  // from government and research. Both are factors on the production figure,
  // never an adjustment to the final GDP. They are applied before the absolute
  // war damage below, so a scar stays proportional to the tile's productivity.
  if (regionalMultiplier !== 1) {
@@ -155,13 +155,14 @@ export function gdpPerCapitaFactors(tile, {
  if (nationalMultiplier !== 1) {
    factors.push({ label: "National modifiers", multiplier: nationalMultiplier });
  }
-  // A warm-water port adds a flat per-capita figure to its whole region, scaled
-  // by the sea tiles beside the city, before war damage is taken off.
-  if (portGdp > 0) {
-    factors.push({ label: "Port", amount: portGdp });
+  // A warm-water port adds a flat production-per-head figure to its whole
+  // region, scaled by the sea tiles beside the city, before war damage is taken
+  // off.
+  if (portProduction > 0) {
+    factors.push({ label: "Port", amount: portProduction });
  }
-  // Natural growth is a flat per-capita gain added on top of the tile's
-  // productivity, growing by a constant amount each day.
+  // Natural growth is a flat production-per-head gain added on top of the
+  // tile's productivity, growing by a constant amount each day.
  if (naturalGrowth > 0) {
    factors.push({ label: "Natural growth", amount: naturalGrowth });
  }
@@ -171,9 +172,9 @@ export function gdpPerCapitaFactors(tile, {
  return factors;
 }

-// Applies the `gdpPerCapitaFactors` list to `base`, in order, never falling
+// Applies the `productionFactors` list to `base`, in order, never falling
 // below zero.
-export function gdpPerCapitaFromFactors(base, factors) {
+export function productionFromFactors(base, factors) {
  let total = base;
  for (const factor of factors) {
    if (factor.amount !== undefined) total += factor.amount;
@@ -181,3 +182,14 @@ export function gdpPerCapitaFromFactors(base, factors) {
  }
  return total > 0 ? total : 0;
 }
+
+// The multiplier product of a `productionFactors` list, ignoring the absolute
+// per-head terms (a port's flat production, natural growth, battle damage).
+// This is what scales a tile's physical output.
+export function productionMultiplier(factors) {
+  let total = 1;
+  for (const factor of factors) {
+    if (factor.multiplier !== undefined) total *= factor.multiplier;
+  }
+  return total > 0 ? total : 0;
+}
@@ -21,8 +21,8 @@ export class TerrainStats {
    return this._value(coords, "populationMultiplier");
  }

-  gdpMultiplier(coords) {
-    return this._value(coords, "gdpMultiplier");
+  productionMultiplier(coords) {
+    return this._value(coords, "productionMultiplier");
  }

  movementCostMultiplier(coords) {
@@ -1,7 +1,7 @@
 import { TestCase } from "./framework/test_case.js";
 import { smallState } from "./framework/helpers.js";
 import { parseKey, key } from "../shared/hex.js";
-import { AIR_STRIKE } from "../shared/data.js";
+import { AIR_STRIKE, RESOURCE_RULES } from "../shared/data.js";

 const BIG_BUDGET = 1.0e15;

@@ -97,8 +97,8 @@ export class AirTest extends TestCase {
    state.budgets.set(0, BIG_BUDGET);
    const shipyard = buildingIndex(state, "shipyard");
    const city = coastalCity(state, 0);
-    this.assertFalse(state.requestBuild(city.id, shipyard), "no port, no shipyard");
-    giveBuilding(state, city, "port");
+    // Every naval city opens the game with a port.
+    this.assertTrue(state.hasCityBuilding(city, "port"), "a naval city starts with a port");
    this.assertTrue(state.requestBuild(city.id, shipyard), "a port unlocks the shipyard");

    // Even with a port, an inland city has no water to launch from.
@@ -160,13 +160,18 @@ export class AirTest extends TestCase {
    this.assertNotNull(target, "there is a target tile within range");
    const defender = state._spawnUnit(target, 1, protoUnit(state, "modern_infantry"));

+    const totalTech = () => state.cities.filter((c) => c.civ === 0)
+      .reduce((sum, c) => sum + (state.getCityResourceStock(c).hightech || 0), 0);
+    const beforeTech = totalTech();
+
    this.assertTrue(state.requestAirStrike([unit.id], defender.coords), "the strike is accepted");
    this.assertEqual(unit.coords.x, city.coords.x, "it has not taken off yet");
+    // A sortie is paid for in munitions, not money.
    this.assertApprox(
-      state.getBudget(0),
-      BIG_BUDGET - AIR_STRIKE.cost,
+      beforeTech - totalTech(),
+      RESOURCE_RULES.combatConsumption.airStrike.hightech,
      1e-6,
-      "the strike was paid for up front"
+      "the sortie spent its high-tech up front"
    );

    state.advanceHour();
@@ -35,18 +35,20 @@ export class AppTest extends TestCase {
      joinSocket.simulateMessage({ t: "assigned", playerId: 2, admin: false, name: "Carol" });
      this.assertFalse(env.$("#screen-game").hasClass("active"), "no game screen before picking");

+      const state = smallState();
+      const britain = state.civilisations.findIndex((civ) => civ.id === "britain");
      joinSocket.simulateMessage({
        t: "choose_civ",
-        civs: [{ index: 1, id: "britain", name: "Britain" }],
+        civs: [{ index: britain, id: "britain", name: "Britain" }],
      });
      this.assertTrue(env.$("#screen-choose").hasClass("active"));
      this.assertSize(env.$("#choose-civs li"), 1);
      env.$("#choose-civs li").first().click();
-      this.assertEqual(joinSocket.lastSent(), { t: "claim_civ", civ: 1 });
+      this.assertEqual(joinSocket.lastSent(), { t: "claim_civ", civ: britain });

-      joinSocket.simulateMessage({ t: "civ_assigned", civ: 1 });
+      joinSocket.simulateMessage({ t: "civ_assigned", civ: britain });
      this.assertTrue(env.$("#screen-game").hasClass("active"));
-      joinSocket.simulateMessage({ t: "game_state", state: smallState().snapshot(1) });
+      joinSocket.simulateMessage({ t: "game_state", state: state.snapshot(britain) });
      this.assertEqual(env.$("#civ-name").text(), "Britain");
      this.assertFalse(env.$("#stat-pop").text() === "0");
    } finally {
@@ -114,19 +116,18 @@ export class AppTest extends TestCase {
      this.assertEqual(socket.lastSent(), { t: "login", name: "adrien", password: "admin" });

      socket.simulateMessage({ t: "assigned", playerId: 1, admin: true, name: "adrien" });
+      const state = smallState();
+      const france = state.civilisations.findIndex((civ) => civ.id === "france");
      socket.simulateMessage({
        t: "choose_civ",
-        civs: [
-          { index: 4, id: "france", name: "France" },
-          { index: 1, id: "britain", name: "Britain" },
-        ],
+        civs: [{ index: france, id: "france", name: "France" }],
      });
-      this.assertEqual(socket.lastSent(), { t: "claim_civ", civ: 4 }, "France is claimed");
+      this.assertEqual(socket.lastSent(), { t: "claim_civ", civ: france }, "France is claimed");
      this.assertFalse(env.$("#screen-choose").hasClass("active"), "the picker is skipped");

-      socket.simulateMessage({ t: "civ_assigned", civ: 4 });
+      socket.simulateMessage({ t: "civ_assigned", civ: france });
      this.assertTrue(env.$("#screen-game").hasClass("active"));
-      socket.simulateMessage({ t: "game_state", state: smallState().snapshot(0) });
+      socket.simulateMessage({ t: "game_state", state: state.snapshot(france) });
      this.assertEqual(env.$("#civ-name").text(), "France");
    } finally {
      teardownDom(env);
@@ -0,0 +1,139 @@
+import { TestCase } from "./framework/test_case.js";
+import { smallState } from "./framework/helpers.js";
+import { HOURS_PER_DAY } from "../shared/game_state/constants.js";
+import { BUDGET_HISTORY_MONTHS } from "../shared/game_state/budget.js";
+
+export class BudgetTest extends TestCase {
+  test_the_opening_month_is_the_only_report() {
+    const state = smallState();
+    const months = state.budgetMonthReports(0);
+    this.assertSize(months, 1, "only the live month exists at the start");
+    this.assertTrue(months[0].isCurrent, "the live month is flagged current");
+    this.assertEqual(months[0].label, "January 2000");
+    this.assertEqual(months[0].expenses.length, 0, "nothing has been spent yet");
+    this.assertEqual(months[0].net, 0, "the month opens balanced");
+  }
+
+  test_spending_is_filed_under_its_category() {
+    const state = smallState();
+    state._spendBudget(0, 1_000, "training");
+    state._spendBudget(0, 4_000, "construction");
+    state._recordBudgetCash(0, "income", 9_000);
+    const report = state.budgetMonthReports(0).at(-1);
+    const byId = new Map(report.expenses.map((entry) => [entry.id, entry]));
+    this.assertApprox(byId.get("training").cash, 1_000);
+    this.assertApprox(byId.get("construction").cash, 4_000);
+    this.assertApprox(report.income, 9_000);
+    this.assertApprox(report.totalCash, 5_000);
+    this.assertApprox(report.net, 4_000);
+  }
+
+  test_a_spend_on_an_empty_treasury_becomes_debt_and_is_recorded() {
+    const state = smallState();
+    state.budgets.set(0, 0);
+    // The government always pays; the overdraft is the central bank's loan.
+    this.assertTrue(state._spendBudget(0, 500, "training"));
+    this.assertLess(state.getBudget(0), 0, "the treasury went into the red");
+    const report = state.budgetMonthReports(0).at(-1);
+    const training = report.expenses.find((entry) => entry.id === "training");
+    this.assertApprox(training.cash, 500);
+  }
+
+  test_a_refund_cancels_the_category() {
+    const state = smallState();
+    state._spendBudget(0, 1_000, "construction");
+    state._refundBudget(0, 1_000, "construction");
+    const report = state.budgetMonthReports(0).at(-1);
+    this.assertEqual(report.expenses.length, 0, "a refunded order does not linger");
+    this.assertEqual(report.net, 0);
+  }
+
+  test_daily_upkeep_records_cash_and_market_value() {
+    const state = smallState();
+    state.advanceHour();
+    for (let i = 0; i < 23; i++) state.advanceHour();
+    const report = state.budgetMonthReports(0).at(-1);
+    const byId = new Map(report.expenses.map((entry) => [entry.id, entry]));
+    for (const id of ["buildings", "units", "works", "transport"]) {
+      const entry = byId.get(id);
+      this.assertNotNull(entry, `${id} upkeep is recorded`);
+      this.assertTrue(entry.economic >= entry.cash - 1e-6, `${id} market value covers its cash`);
+    }
+  }
+
+  test_rolling_a_month_freezes_a_digest_and_resets() {
+    const state = smallState();
+    state._spendBudget(0, 2_000, "training");
+    // January 2000 has 31 days.
+    for (let i = 0; i < 31 * HOURS_PER_DAY; i++) state.tickHour();
+    const months = state.budgetMonthReports(0);
+    this.assertSize(months, 2, "January is frozen behind the live February");
+    this.assertEqual(months[0].label, "January 2000");
+    this.assertTrue(!months[0].isCurrent, "the frozen month is not current");
+    this.assertEqual(months[1].label, "February 2000");
+    this.assertTrue(months[1].isCurrent, "the live month is February");
+    const training = months[0].expenses.find((entry) => entry.id === "training");
+    this.assertApprox(training.cash, 2_000, 1e-6);
+    this.assertEqual(
+      months[1].expenses.find((entry) => entry.id === "training"),
+      undefined,
+      "the new month starts empty"
+    );
+  }
+
+  test_the_history_is_capped() {
+    const state = smallState();
+    for (let i = 0; i < BUDGET_HISTORY_MONTHS + 5; i++) state._rolloverBudget(24000 + i);
+    this.assertSize(state.budgetHistory, BUDGET_HISTORY_MONTHS, "only two years are kept");
+  }
+
+  test_resource_trade_is_mirrored_into_the_month() {
+    const state = smallState();
+    state._recordResourceSpend(0, "goods", 5_000, "steel");
+    state._recordResourceEarn(0, "steel", 2_000);
+    const report = state.budgetMonthReports(0).at(-1);
+    const trade = report.resourceTrade.find((entry) => entry.id === "steel");
+    this.assertNotNull(trade);
+    this.assertApprox(trade.bought, 5_000);
+    this.assertApprox(trade.sold, 2_000);
+  }
+
+  test_expense_rows_carry_their_resource_detail() {
+    const state = smallState();
+    state._recordBudgetCash(0, "buildings", -500);
+    state._recordBudgetCategoryResource(0, "buildings", "steel", 300);
+    state._recordBudgetCategoryResource(0, "buildings", "hightech", 200);
+    const report = state.budgetMonthReports(0).at(-1);
+    const buildings = report.expenses.find((entry) => entry.id === "buildings");
+    this.assertApprox(buildings.cash, 500);
+    this.assertEqual(buildings.buys.length, 2, "both resources are listed");
+    const steel = buildings.buys.find((entry) => entry[0] === "steel");
+    this.assertApprox(steel[1], 300);
+  }
+
+  test_upkeep_records_the_resources_it_bought() {
+    const state = smallState();
+    // Empty the stores so the day's upkeep has to be bought on the market.
+    for (const city of state.cities) {
+      const store = state.getCityResourceStock(city);
+      store.steel = 0;
+      store.hightech = 0;
+    }
+    state.budgets.set(0, 1.0e15);
+    for (let i = 0; i < HOURS_PER_DAY; i++) state.tickHour();
+    const report = state.budgetMonthReports(0).at(-1);
+    const buildings = report.expenses.find((entry) => entry.id === "buildings");
+    this.assertNotNull(buildings, "building upkeep is recorded");
+    this.assertGreater(buildings.buys.length, 0, "the row names the resource it bought");
+  }
+
+  test_the_snapshot_ships_the_month_reports() {
+    const state = smallState();
+    const snapshot = state.snapshot(0);
+    const months = snapshot.viewerStats.budgetMonths;
+    this.assertGreaterOrEqual(months.length, 1);
+    const current = months[months.length - 1];
+    this.assertTrue(current.isCurrent, "the last shipped report is the live month");
+    this.assertTrue(Array.isArray(current.expenses), "the report carries its expenses");
+  }
+}
@@ -108,21 +108,12 @@ export class CombatTest extends TestCase {
  test_battle_triples_the_fighting_unit_upkeep() {
    const state = smallState();
    const { attacker } = engagement(state);
-    const proto = state.protoUnits[attacker.proto];
-    const idleUpkeep = state.getPlayerUpkeep(0) - proto.upkeep * 2;
-    const idleUnits = state.budgetBreakdown(0).unitUpkeep.total - proto.upkeep * 2;
-    this.assertApprox(
-      state.getPlayerUpkeep(0) - idleUpkeep,
-      proto.upkeep * 2,
-      1e-9,
-      "the battle premium is twice the base upkeep"
-    );
-    this.assertApprox(
-      state.budgetBreakdown(0).unitUpkeep.total - idleUnits,
-      proto.upkeep * 2,
-      1e-9,
-      "the budget breakdown reflects the premium"
+    const battle = state._battleUnitIds();
+    this.assertTrue(battle.has(attacker.id), "the attacker is in battle");
+    const multiplier = state._statusUpkeepMultiplier(
+      state._effectiveStatuses(attacker, true)
    );
+    this.assertGreater(multiplier, 1, "a unit in battle burns more material upkeep");
  }

  test_a_blocked_move_with_no_route_is_abandoned() {
@@ -434,7 +425,7 @@ export class CombatTest extends TestCase {
    );
    this.assertApprox(
      state.getTileGdpPerCapita(b),
-      perCapita * (1 - BATTLE.gdpPerCapitaLossPerDay),
+      perCapita * (1 - BATTLE.productionLossPerDay),
      1e-6,
      "the tile loses GDP per capita"
    );
@@ -446,19 +437,19 @@ export class CombatTest extends TestCase {
    const k = key(b.x, b.y);
    const perCapita = state.getTileGdpPerCapita(b);
    state._tickBattleTiles();
-    const deficit = state.tileBattleGdpDeficit.get(k);
-    this.assertApprox(deficit, perCapita * BATTLE.gdpPerCapitaLossPerDay, 1e-6);
+    const deficit = state.tileBattleProductionDeficit.get(k);
+    this.assertApprox(deficit, perCapita * BATTLE.productionLossPerDay, 1e-6);
    const start = state.tileBattleRecoveryStart.get(k);
    this.assertEqual(start, BATTLE.recoveryDelayDays * DAY, "recovery waits thirty days");

    state.totalHours = start - 1;
-    state._tickGdpRecovery();
-    this.assertApprox(state.tileBattleGdpDeficit.get(k), deficit, 1e-9, "nothing recovers early");
+    state._tickProductionRecovery();
+    this.assertApprox(state.tileBattleProductionDeficit.get(k), deficit, 1e-9, "nothing recovers early");

    state.totalHours = start;
-    state._tickGdpRecovery();
+    state._tickProductionRecovery();
    this.assertApprox(
-      state.tileBattleGdpDeficit.get(k),
+      state.tileBattleProductionDeficit.get(k),
      deficit - BATTLE.recoveryPerDay,
      1e-9,
      "recovery begins at $100 a day"
@@ -466,9 +457,9 @@ export class CombatTest extends TestCase {

    for (let day = 0; day < Math.ceil(deficit / BATTLE.recoveryPerDay) + 1; day++) {
      state.totalHours += DAY;
-      state._tickGdpRecovery();
+      state._tickProductionRecovery();
    }
-    this.assertFalse(state.tileBattleGdpDeficit.has(k), "the wound heals completely");
+    this.assertFalse(state.tileBattleProductionDeficit.has(k), "the wound heals completely");
    this.assertFalse(state.tileBattleRecoveryStart.has(k), "and the clock is cleared");
  }

@@ -477,9 +468,9 @@ export class CombatTest extends TestCase {
    const { b } = joinBattleOn(state, ownedLandPair(state));
    const k = key(b.x, b.y);
    const before = state.getTileGdpPerCapita(b);
-    this.assertFalse(state.tileBattleGdpDeficit.has(k), "the tile is untouched at first");
+    this.assertFalse(state.tileBattleProductionDeficit.has(k), "the tile is untouched at first");
    for (let hour = 0; hour < DAY; hour++) state.tickHour();
-    this.assertTrue(state.tileBattleGdpDeficit.has(k), "the daily tick records the scar");
+    this.assertTrue(state.tileBattleProductionDeficit.has(k), "the daily tick records the scar");
    this.assertLess(state.getTileGdpPerCapita(b), before, "and the tile is worth less");
    this.assertEqual(state.tileBattleRecoveryStart.get(k), DAY + BATTLE.recoveryDelayDays * DAY);
  }
@@ -645,10 +636,12 @@ function ownedLandPair(state) {
  for (const cell of state.landCells) {
    if (state.civAt(cell) < 0) continue;
    if (state.unitAt(cell) || state.cityAt(cell)) continue;
+    if (state.tileImprovements.has(key(cell.x, cell.y))) continue;
    for (const neighbour of state.topology.neighbours(cell.x, cell.y)) {
      if (!state._isLand(neighbour)) continue;
      if (state.civAt(neighbour) < 0) continue;
      if (state.unitAt(neighbour) || state.cityAt(neighbour)) continue;
+      if (state.tileImprovements.has(key(neighbour.x, neighbour.y))) continue;
      return { a: { x: cell.x, y: cell.y }, b: { x: neighbour.x, y: neighbour.y } };
    }
  }
@@ -17,6 +17,7 @@ import {
  PILLAGE,
  pillageSteps,
  POLICIES,
+  RESOURCE_BUILDINGS,
 } from "../shared/data.js";

 export class DataTest extends TestCase {
@@ -27,6 +28,13 @@ export class DataTest extends TestCase {
    this.assertEqual(technologyById("scientific_method"), TECHNOLOGIES[0]);
  }

+  test_resource_building_output_is_scaled_up() {
+    // One work stands for a whole industry: the authored output is multiplied
+    // tenfold so fewer of them stand on the map.
+    const mill = RESOURCE_BUILDINGS.find((b) => b.id === "steel_mill");
+    this.assertApprox(mill.outputPerDay, 20_000, 1e-6);
+  }
+
  test_unknown_lookups_return_null() {
    this.assertNull(protoUnitById("nope"));
    this.assertNull(buildingById("nope"));
@@ -57,14 +65,14 @@ export class DataTest extends TestCase {
    const one = pillageSteps(100000, 1);
    this.assertApprox(one.steps[0].removed, 10000, 1e-6);
    this.assertApprox(one.steps[0].heal, 10, 1e-9);
-    this.assertApprox(one.gdpMultiplier, PILLAGE.gdpPenalty, 1e-9);
+    this.assertApprox(one.productionMultiplier, PILLAGE.productionPenalty, 1e-9);

    const two = pillageSteps(100000, 2);
    this.assertApprox(two.steps[0].removed, 10000, 1e-6);
    this.assertApprox(two.steps[1].removed, 9000, 1e-6);
    this.assertApprox(two.steps[1].heal, 9, 1e-9);
    this.assertApprox(two.steps[1].remaining, 81000, 1e-6);
-    this.assertApprox(two.gdpMultiplier, 0.49, 1e-9);
+    this.assertApprox(two.productionMultiplier, 0.49, 1e-9);
  }

  test_trainable_units_exist_in_the_catalogue() {
@@ -133,7 +141,7 @@ export class DataTest extends TestCase {
      shelters: "civilian_shelter",
      aa_building: "air_defense",
      shipyard: "parallel_building",
-      port: "port_gdp",
+      port: "port_production",
      airport: "air_immigration",
    };
    for (const [id, mechanic] of Object.entries(expected)) {
@@ -196,7 +204,7 @@ export class DataTest extends TestCase {
    this.assertEqual(tundra.terrainClass, "Land", "tundra is land");
    this.assertEqual(tundra.defenseBonus, 0, "tundra stays flat");
    this.assertApprox(tundra.populationMultiplier, 0.05, 1e-9);
-    this.assertApprox(tundra.gdpMultiplier, 0.2, 1e-9);
+    this.assertApprox(tundra.productionMultiplier, 0.2, 1e-9);
    this.assertApprox(tundra.movementCostMultiplier, 2.0, 1e-9);
  }
 }
@@ -71,6 +71,7 @@ export function mapLayers($) {
    highlight: $("#layer-highlight"),
    paths: $("#layer-paths"),
    targets: $("#layer-targets"),
+    resources: $("#layer-resources"),
    entities: $("#layer-entities"),
    labels: $("#layer-labels"),
  };
@@ -109,6 +110,19 @@ export function unitsOf(state, civ) {
  return state.units.filter((unit) => unit.civ === civ).length;
 }

+// Removes the port every naval city opens with, so a GDP-sensitive test starts
+// from the same terrain-only economy it would have had before ports were seeded.
+export function stripPorts(state, civ = null) {
+  const index = state.protoBuildings.findIndex((building) => building.id === "port");
+  if (index < 0) return;
+  for (const city of state.cities) {
+    if (civ !== null && city.civ !== civ) continue;
+    if (city.buildings[index]) delete city.buildings[index];
+  }
+  state._gdpPerCapitaCache.clear();
+  state._touchModifiers();
+}
+
 export function snapshotUnit(state, unitId, viewer = 0) {
  return (state.snapshot(viewer).units || []).find((u) => u.id === unitId) || null;
 }
@@ -120,7 +134,7 @@ export function gdpBuilding(overrides = {}) {
    baseCost: 100,
    costAlpha: 2.0,
    refundFraction: 0.5,
-    effects: [{ stat: "gdp", baseValue: 0.5, exponent: 1.0 }],
+    effects: [{ stat: "production", baseValue: 0.5, exponent: 1.0 }],
    ...overrides,
  };
 }
@@ -1,10 +1,12 @@
 import { TestCase } from "./framework/test_case.js";
 import { setupDom, teardownDom } from "./framework/dom.js";
 import { GameScreen } from "../client/js/game_screen.js";
-import { BUILDINGS, CIVILISATIONS, TECHNOLOGIES, PROTO_UNITS, ECONOMY } from "../shared/data.js";
+import { BUILDINGS, CIVILISATIONS, TECHNOLOGIES, PROTO_UNITS, ECONOMY, TRANSPORT_IMPROVEMENTS } from "../shared/data.js";
 import { HOURS_PER_DAY } from "../shared/game_state/constants.js";
 import { hoursInNextMonth } from "../shared/game_clock.js";
 import { compact } from "../shared/text_format.js";
+import { tileImprovementResourceCost } from "../shared/resources.js";
+import { quotedBuildCost, marketPricesFrom } from "../client/js/modals/format.js";
 import { parseKey } from "../shared/hex.js";
 import { smallState, adjacentLand, grantBuilding } from "./framework/helpers.js";

@@ -51,12 +53,12 @@ export class GameScreenTest extends TestCase {
      const territory = screen.map.territory;
      const regions = screen.map.regions;
      const ethnicity = screen._tileEthnicity;
-      const baseline = screen._gdpBaseline;
+      const baseline = screen._productionBaseline;
      // A second snapshot with no state change carries the same versions, so
      // none of the big per-tile maps should be rebuilt.
      screen.onState(state.snapshot(0));
      this.assert(population === screen._population, "population map is reused");
-      this.assert(baseline === screen._gdpBaseline, "the growth baseline is reused");
+      this.assert(baseline === screen._productionBaseline, "the growth baseline is reused");
      this.assert(territory === screen.map.territory, "territory map is reused");
      this.assert(regions === screen.map.regions, "region map is reused");
      this.assert(ethnicity === screen._tileEthnicity, "ethnicity map is reused");
@@ -77,7 +79,7 @@ export class GameScreenTest extends TestCase {
      const capital = state.cities.find((c) => c.civ === 0 && c.isCapital);
      grantBuilding(state, capital, "barracks");
      screen.onState(state.snapshot(0));
-      this.assertEqual(env.$("#civ-name").text(), "France");
+      this.assertEqual(env.$("#civ-name").text(), state.civilisations[0].name);
      this.assertEqual(env.$("#player-name").text(), "Carol");
      this.assertTrue(env.$("#stat-pop").text() !== "0");
      this.assertTrue(env.$("#stat-date").text().includes("2000"));
@@ -616,37 +618,21 @@ export class GameScreenTest extends TestCase {
      screen.map.onTileRequested(capital.coords);
      this.assertFalse(env.$("#tile-info").hasClass("hidden"));
      this.assertTrue(env.$("#tile-coords").text().includes("Tile"));
-      this.assertTrue(env.$("#tile-gdp").text().includes("GDP/capita"));
+      // The panel leads with what the tile produces, and GDP is only shown for
+      // its region.
      this.assertTrue(
-        env.$("#tile-gdp").text().includes("Capital"),
-        "the tile panel explains the capital GDP bonus"
+        env.$("#tile-gdp").text().includes("Region GDP/capita"),
+        "GDP is shown at the region level"
+      );
+      this.assertGreater(
+        env.$("#tile-production .tile-prod-row").length,
+        0,
+        "the tile panel lists the resources it produces"
+      );
+      this.assertTrue(
+        env.$("#tile-production").text().includes("Food"),
+        "the capital's people grow food"
      );
-
-      screen._renderTileGdp({
-        base: 10000,
-        factors: [
-          { label: "Terrain", multiplier: 1 },
-          { label: "City", multiplier: 2 },
-          { label: "Battle damage", amount: 0 },
-        ],
-        total: 20000,
-      });
-      const gdpText = env.$("#tile-gdp").text();
-      this.assertFalse(gdpText.includes("Terrain"), "a no-op multiplier is hidden");
-      this.assertFalse(gdpText.includes("Battle damage"), "a zero modifier is hidden");
-      this.assertTrue(gdpText.includes("City"), "a real modifier is still shown");
-
-      screen._renderTileGdp({
-        base: 10000,
-        factors: [
-          { label: "Natural growth", amount: 150 },
-          { label: "Battle damage", amount: -50 },
-        ],
-        total: 10100,
-      });
-      const amountText = env.$("#tile-gdp").text();
-      this.assertTrue(amountText.includes("Natural growth +€150"), "a gain shows a plus");
-      this.assertTrue(amountText.includes("Battle damage −€50"), "a loss keeps its minus");

      const unit = state.units.find((u) => u.civ === 0);
      screen.map.onUnitSelected(unit.id);
@@ -1015,7 +1001,7 @@ export class GameScreenTest extends TestCase {
      await screen.map.onMoveOrdered([unit.id], goal);
      this.assertFalse(env.$("#modal-confirm").hasClass("hidden"), "the war prompt opens");
      this.assertEmpty(network.orders, "nothing is sent before confirming");
-      this.assertTrue(env.$("#confirm-message").text().includes("Britain"));
+      this.assertTrue(env.$("#confirm-message").text().includes(state.civilisations[1].name));

      env.$("#confirm-ok").click();
      this.assertEqual(network.orders[0], { type: "move", unit: unit.id, coords: [900, 900] });
@@ -1079,7 +1065,7 @@ export class GameScreenTest extends TestCase {
      screen.onState(smallState().snapshot(0));
      env.$("#civ-flag").click();
      env.$("#modal-nation .tab[data-tab=diplomacy]").click();
-      const row = env.$("#diplomacy-list tbody tr").first();
+      const row = env.$("#diplomacy-list tbody tr:not(.local-nation)").first();
      this.assertTrue(row.find(".name").text().length > 0);
      row.find("button").click();
      this.assertEqual(network.orders[0].type, "declare_war");
@@ -1124,7 +1110,7 @@ export class GameScreenTest extends TestCase {
      screen.onState(state.snapshot(0));
      env.$("#news-button").click();
      this.assertFalse(env.$("#modal-news").hasClass("hidden"));
-      this.assertTrue(env.$("#news-list").text().includes("declared war on Britain"));
+      this.assertTrue(env.$("#news-list").text().includes(`declared war on ${state.civilisations[1].name}`));
      screen.leave();
    } finally {
      teardownDom(env);
@@ -1144,7 +1130,7 @@ export class GameScreenTest extends TestCase {
      state.requestDeclareWar(0, 1);
      screen.onState(state.snapshot(0));
      this.assertSize(env.$("#game-feed .feed-line"), 1);
-      this.assertTrue(env.$("#game-feed .feed-line").text().includes("declared war on Britain"));
+      this.assertTrue(env.$("#game-feed .feed-line").text().includes(`declared war on ${state.civilisations[1].name}`));
      screen.leave();
    } finally {
      teardownDom(env);
@@ -1530,7 +1516,7 @@ export class GameScreenTest extends TestCase {
      const coords = state.landCells.find((cell) => {
        const k = `${cell.x},${cell.y}`;
        return state.civAt(cell) === 0 && !state.cityAt(cell) &&
-          !state.roads.has(k) && !state.railways.has(k);
+          !state.roads.has(k) && !state.railways.has(k) && !state.tileImprovements.has(k);
      });
      this.assertNotNull(coords, "the player owns a bare land tile");
      screen._showTile(coords);
@@ -1538,12 +1524,32 @@ export class GameScreenTest extends TestCase {
      this.assertEqual(options.length, 2, "road and railway are listed");
      this.assertFalse(options.eq(0).prop("disabled"), "the road option is clickable");
      this.assertFalse(options.eq(1).prop("disabled"), "the railway option is clickable");
-      // Each is a square icon with its name in the tooltip and cost beneath.
+      // Each is a square icon with its name in the tooltip and its resource and
+      // money cost beneath.
      this.assertTrue(
        options.eq(0).find("img.improvement-icon").attr("src").endsWith("icon_road.svg"),
        "the road button shows its icon"
      );
-      this.assertEqual(options.eq(0).find(".improvement-cost").text(), "€50M", "cost under the icon");
+      const costText = options.eq(0).find(".improvement-cost").text();
+      this.assertTrue(costText.includes("5000 t"), `the steel cost is shown: ${costText}`);
+      this.assertTrue(costText.includes("100 GWh"), `the energy cost is shown: ${costText}`);
+      // The money figure is the build cost plus the material bill at today's
+      // market prices, not the raw build cost.
+      const roadProto = TRANSPORT_IMPROVEMENTS.find((i) => i.id === "road");
+      const expectedCost = quotedBuildCost(
+        roadProto.buildCost,
+        tileImprovementResourceCost(roadProto),
+        marketPricesFrom(screen.snapshot)
+      );
+      this.assertTrue(
+        costText.includes(`£${compact(expectedCost)}`),
+        `the market price is shown: ${costText}`
+      );
+      this.assertEqual(
+        options.eq(0).find(".improvement-cost img.cost-icon").length,
+        2,
+        "steel and energy carry resource icons"
+      );
      this.assertTrue(
        options.eq(0).attr("title").startsWith("Road"),
        "the name is the tooltip"
@@ -1556,10 +1562,16 @@ export class GameScreenTest extends TestCase {
      this.assertEqual(order.improvement, "road");

      // A tile that already carries the improvement greys it out, keeps the
-      // upgrade and offers a remove control.
+      // upgrade and offers a remove control. The seeded starter industry also
+      // puts works on network tiles, so clear any off this one first.
      const road = Array.from(state.roads).map((k) => k.split(",").map(Number))[0];
+      const roadKey = `${road[0]},${road[1]}`;
+      state.tileImprovements.delete(roadKey);
+      state.tileImprovementOwner.delete(roadKey);
+      state.tileImprovementHp.delete(roadKey);
+      screen.onState(state.snapshot(0));
      screen._showTile({ x: road[0], y: road[1] });
-      const again = env.$("#tile-improvement-actions .improvement-btn").not(".remove");
+      const again = env.$("#tile-improvement-actions .transport-btn").not(".remove");
      this.assertTrue(again.eq(0).prop("disabled"), "the built road is greyed out");
      this.assertFalse(again.eq(1).prop("disabled"), "the railway upgrade stays available");
      const $remove = env.$("#tile-improvement-actions .improvement-btn.remove");
@@ -1575,6 +1587,71 @@ export class GameScreenTest extends TestCase {
    }
  }

+  async test_improvement_buttons_are_grouped_by_category() {
+    const env = await setupDom();
+    try {
+      const screen = new GameScreen(stubNetwork(), makeConfig());
+      screen.enter();
+      const state = smallState();
+      state.budgets.set(0, 1.0e15);
+      screen.onState(state.snapshot(0));
+      const coords = state.landCells.find((cell) => {
+        const k = `${cell.x},${cell.y}`;
+        return state.civAt(cell) === 0 && !state.cityAt(cell) && !state.tileImprovements.has(k);
+      });
+      this.assertNotNull(coords, "the player owns a bare land tile");
+      screen._showTile(coords);
+      const labels = env.$("#tile-improvement-actions .improvement-category")
+        .map((_, el) => env.$(el).text())
+        .get();
+      this.assertEqual(
+        labels.join(","),
+        "Military,Transportation,Economic",
+        "the categories are labelled in order"
+      );
+      const firstClasses = env.$("#tile-improvement-actions .improvement-row")
+        .map((_, el) => env.$(el).find(".improvement-btn").first().attr("class"))
+        .get();
+      this.assertTrue(firstClasses[0].includes("tile-btn"), "military works come first");
+      this.assertTrue(firstClasses[1].includes("transport-btn"), "transport comes second");
+      this.assertTrue(firstClasses[2].includes("resource-btn"), "economic producers come last");
+      screen.leave();
+    } finally {
+      teardownDom(env);
+    }
+  }
+
+  async test_improvement_cost_tracks_market_prices() {
+    const env = await setupDom();
+    try {
+      const screen = new GameScreen(stubNetwork(), makeConfig());
+      screen.enter();
+      const state = smallState();
+      state.budgets.set(0, 1.0e15);
+      const coords = state.landCells.find((cell) => {
+        const k = `${cell.x},${cell.y}`;
+        return state.civAt(cell) === 0 && !state.cityAt(cell) && !state.tileImprovements.has(k);
+      });
+      this.assertNotNull(coords, "the player owns a bare land tile");
+      screen.onState(state.snapshot(0));
+      screen._showTile(coords);
+      const before = env.$("#tile-improvement-actions .transport-btn").eq(0)
+        .find(".improvement-cost").text();
+      // A jump in the world steel price raises the quoted price, without
+      // changing the amount of steel shown.
+      state.setResourcePrice("steel", state.getResourcePrice("steel") * 3);
+      screen.onState(state.snapshot(0));
+      screen._showTile(coords);
+      const after = env.$("#tile-improvement-actions .transport-btn").eq(0)
+        .find(".improvement-cost").text();
+      this.assertNotEqual(before, after, `the quote moved: ${before} -> ${after}`);
+      this.assertTrue(after.includes("5000 t"), "the steel amount is unchanged");
+      screen.leave();
+    } finally {
+      teardownDom(env);
+    }
+  }
+
  async test_tile_panel_shows_improvement_build_progress() {
    const env = await setupDom();
    try {
@@ -1584,7 +1661,8 @@ export class GameScreenTest extends TestCase {
      state.budgets.set(0, 1.0e15);
      const coords = state.landCells.find((cell) => {
        const k = `${cell.x},${cell.y}`;
-        return state.civAt(cell) === 0 && !state.cityAt(cell) && !state.unitAt(cell);
+        return state.civAt(cell) === 0 && !state.cityAt(cell) &&
+          !state.unitAt(cell) && !state.tileImprovements.has(k);
      });
      this.assertNotNull(coords, "the player owns a bare land tile");
      this.assertTrue(
@@ -1765,7 +1843,7 @@ export class GameScreenTest extends TestCase {
      const sign = expected < 0 ? "−" : "+";
      this.assertEqual(
        env.$("#stat-budget").closest(".stat").attr("data-tooltip"),
-        `${sign}€${compact(Math.abs(expected))}/mo`
+        `${sign}£${compact(Math.abs(expected))}/mo`
      );
      // Popularity speaks through the same bubble, not a native title.
      const $approval = env.$("#stat-approval").closest(".stat");
@@ -1777,33 +1855,23 @@ export class GameScreenTest extends TestCase {
    }
  }

-  async test_the_tile_gdp_breakdown_includes_natural_growth() {
+  async test_the_tile_panel_lists_produced_resources() {
    const env = await setupDom();
    try {
      const screen = new GameScreen(stubNetwork(), makeConfig());
      screen.enter();
      const state = smallState();
-      state.totalHours = 10 * HOURS_PER_DAY;
      screen.onState(state.snapshot(0));
-      const k = state.tileGdpBaseline.keys().next().value;
-      const coords = parseKey(k);
-      const shipped = Math.round(state.tileGdpBaseline.get(k));
-      const expected = shipped * ECONOMY.naturalGdpGrowthPerDay * 10;
-      this.assertApprox(
-        screen._naturalTileGdpGrowth(k),
-        expected,
-        1e-6,
-        "the browser mirrors the server's growth"
+      const capital = state.cities.find((c) => c.civ === 0 && c.isCapital);
+      screen._showTile({ x: capital.coords.x, y: capital.coords.y });
+      const $food = env.$("#tile-production .tile-prod-row").filter((_, el) =>
+        env.$(el).text().includes("Food")
      );
-      const breakdown = screen._tileGdpBreakdown(
-        coords,
-        0,
-        state.cityAt(coords),
-        screen.map.getTile(coords)
-      );
-      const factor = breakdown.factors.find((f) => f.label === "Natural growth");
-      this.assertNotNull(factor, "the breakdown names the growth");
-      this.assertApprox(factor.amount, expected, 1e-6, "and adds it to the total");
+      this.assertEqual($food.length, 1, "the capital grows food");
+      this.assertTrue($food.text().includes("/day"), "its output is per day");
+      // The modifiers that shape the output ride along in the row's tooltip.
+      this.assertNotNull($food.attr("title"), "the row explains its modifiers");
+      this.assertTrue($food.attr("title").includes("Capital"), `cites the capital bonus: ${$food.attr("title")}`);
      screen.leave();
    } finally {
      teardownDom(env);
@@ -416,7 +416,7 @@ export class GameServerOrdersTest extends TestCase {
    const choose = network.sent.find((m) => m.peerId === 2 && m.message.t === "choose_civ");
    this.assertNotNull(choose, "the joiner is offered a choice");
    this.assertEqual(choose.message.civs.map((c) => c.index), [1]);
-    this.assertEqual(choose.message.civs[0].id, "britain");
+    this.assertEqual(choose.message.civs[0].id, server.state.civilisations[1].id);
    this.assertEqual(server.peerCiv.get(2), -1, "no nation until the player picks");
  }

@@ -585,7 +585,7 @@ export class GameServerLobbyTest extends TestCase {
    this.assertEqual(game.seed, SEED);
    this.assertEqual(game.id, SEED);
    this.assertSize(game.civs, 2);
-    this.assertEqual(game.civs[0], "France");
+    this.assertEqual(game.civs.slice().sort(), ["Britain", "France"]);
    this.assertEqual(game.players, 0);
    this.assertTrue(game.date.includes("2000"));
  }
@@ -1,7 +1,9 @@
 import { TestCase } from "./framework/test_case.js";
 import { smallState, cityOf, gdpBuilding, grantBuilding } from "./framework/helpers.js";
 import { key } from "../shared/hex.js";
-import { ECONOMY, EFFECT_BUDGET_INCOME, EFFECT_RESEARCH } from "../shared/data.js";
+import { ECONOMY, EFFECT_BUDGET_INCOME, EFFECT_RESEARCH, RESOURCE_RULES } from "../shared/data.js";
+import { tileFoodOutput } from "../shared/resources.js";
+import { DAYS_PER_YEAR } from "../shared/game_state/constants.js";

 const BIG_BUDGET = 1.0e15;

@@ -116,17 +118,54 @@ export class GameStateBuildingsTest extends TestCase {
        return tile && tile.terrainClass === "Sea";
      }).length;
    this.assertGreater(sea, 0, "the city touches the sea");
+    const portIndex = state.protoBuildings.findIndex((b) => b.id === "port");
+    // A naval city already starts with one port level.
+    this.assertEqual(city.buildings[portIndex], 1, "the seeded port is there");
+    city.buildings[portIndex] = 0;
+    state._gdpPerCapitaCache.clear();
    const sample = state.regionTiles(city).find((coords) => !state.cityAt(coords)) || state.regionTiles(city)[0];
+    // Isolate the port's GDP bonus: the port also lifts food output, which
+    // feeds back into the production-based base. That is tested separately.
+    const foodMultiplier = state._regionFoodMultiplier;
+    state._regionFoodMultiplier = () => 1;
    const before = state.getTileGdpPerCapita(sample);

-    grantBuilding(state, city, "port", 2);
+    city.buildings[portIndex] = 2;
    state._gdpPerCapitaCache.clear();
    const after = state.getTileGdpPerCapita(sample);
+    state._regionFoodMultiplier = foodMultiplier;

    // +1000 per port level for each neighbouring sea tile, on every region tile.
    this.assertApprox(after - before, 1000 * sea * 2, 1e-6, "the port lifts the whole region");
  }

+  test_port_lifts_its_regions_food_output() {
+    const state = smallState();
+    const city = state.cities.find((c) => c.civ === 0 && state.isCoastalCity(c));
+    this.assertNotNull(city, "the nation has a coastal city");
+    const sea = state.topology
+      .neighbours(city.coords.x, city.coords.y)
+      .filter((n) => {
+        const tile = state.tiles[key(n.x, n.y)];
+        return tile && tile.terrainClass === "Sea";
+      }).length;
+    this.assertGreater(sea, 0, "the city touches the sea");
+    const portIndex = state.protoBuildings.findIndex((b) => b.id === "port");
+    city.buildings[portIndex] = 0;
+    const before = state._regionProductionValue(city);
+    city.buildings[portIndex] = 1;
+    const after = state._regionProductionValue(city);
+    // The port adds 5% of the region's food output for each adjacent sea tile.
+    const foodValue = state.regionTiles(city).reduce((sum, coords) => {
+      const k = key(coords.x, coords.y);
+      const tile = state.tiles[k];
+      const population = state.tilePopulation.get(k) || 0;
+      if (population <= 0) return sum;
+      return sum + tileFoodOutput(tile) * state.getResourcePrice("food");
+    }, 0) * DAYS_PER_YEAR;
+    this.assertApprox(after - before, foodValue * 0.05 * sea, foodValue * 1e-6, "the port grows more food");
+  }
+
  test_request_build_charges_budget_and_raises_the_level() {
    const state = smallState();
    state.budgets.set(0, BIG_BUDGET);
@@ -176,11 +215,13 @@ export class GameStateBuildingsTest extends TestCase {
    this.assertEqual(state.getCityBuildingLevel(city, index), 2);
  }

-  test_request_build_rejects_when_unaffordable() {
+  test_request_build_goes_ahead_on_an_empty_treasury() {
    const state = smallState();
    state.budgets.set(0, 0);
    const index = this.addBuilding(state, gdpBuilding());
-    this.assertFalse(state.requestBuild(cityOf(state, 0).id, index));
+    // The government can always pay, running an overdraft with the central bank.
+    this.assertTrue(state.requestBuild(cityOf(state, 0).id, index));
+    this.assertLess(state.getBudget(0), 0, "the treasury went into debt");
  }

  test_request_build_has_no_level_cap() {
@@ -218,17 +259,19 @@ export class GameStateBuildingsTest extends TestCase {
    this.assertFalse(state.requestDemolish(city.id, index), "nothing left to demolish");
  }

-  test_building_upkeep_is_added_to_player_upkeep() {
+  test_building_upkeep_is_added_to_material_upkeep() {
    const state = smallState();
    state.budgets.set(0, BIG_BUDGET);
    const index = this.addBuilding(
      state,
      gdpBuilding({ baseCost: 10_000, costAlpha: 1.0 })
    );
-    const before = state.getPlayerUpkeep(0);
+    const before = state.getBuildingUpkeep(0);
    this.assertTrue(state.requestBuild(cityOf(state, 0).id, index));
    this.advanceUntilIdle(state);
-    this.assertApprox(state.getPlayerUpkeep(0), before + 100);
+    // 5e-7 t of steel and 1e-3 kWh of energy per euro of the level's cost.
+    this.assertApprox(state.getBuildingUpkeep(0).steel, before.steel + 0.005, 1e-9);
+    this.assertApprox(state.getBuildingUpkeep(0).energy, before.energy + 10, 1e-9);
  }

  test_research_buildings_accumulate_points_each_hour() {
@@ -264,16 +307,17 @@ export class GameStateBuildingsTest extends TestCase {
    this.assertHas(breakdown, "buildingUpkeep");
    this.assertHas(breakdown, "unitUpkeep");
    this.assertHas(breakdown, "transportUpkeep");
-    this.assertApprox(breakdown.buildingUpkeep.total, 100);
-    this.assertApprox(
-      breakdown.unitUpkeep.total,
-      state.getPlayerUpkeep(0) -
-        breakdown.buildingUpkeep.total -
-        breakdown.campaignUpkeep.total -
-        breakdown.transportUpkeep.total
-    );
-    const expected = state.getPlayerGdp(0) * ECONOMY.budgetGdpRate * (1 + breakdown.income.modifier);
-    this.assertApprox(breakdown.income.total, expected);
+    // Upkeep lines are the market value of the materials the nation must buy.
+    const expected = state._upkeepCost(state.getBuildingUpkeep(0));
+    this.assertApprox(breakdown.buildingUpkeep.total, expected, 1e-6);
+    // The only direct money upkeep left is propaganda.
+    this.assertApprox(state.getPlayerUpkeep(0), breakdown.campaignUpkeep.total, 1e-9);
+    const expected_net = breakdown.income.total - breakdown.buildingUpkeep.total -
+      breakdown.unitUpkeep.total - breakdown.campaignUpkeep.total -
+      breakdown.transportUpkeep.total - breakdown.tileUpkeep.total;
+    this.assertApprox(breakdown.net, expected_net, 1e-6);
+    const income = state.getPlayerGdp(0) * ECONOMY.budgetGdpRate * (1 + breakdown.income.modifier);
+    this.assertApprox(breakdown.income.total, income, 1e-6);
  }

  test_budget_breakdown_names_income_sources() {
@@ -1,5 +1,5 @@
 import { TestCase } from "./framework/test_case.js";
-import { smallState } from "./framework/helpers.js";
+import { smallState, stripPorts } from "./framework/helpers.js";
 import { GOVERNMENTS } from "../shared/data.js";

 const BIG_BUDGET = 1.0e15;
@@ -30,14 +30,19 @@ export class GameStateGovernmentTest extends TestCase {
    this.assertFalse(state.requestSetGovernment(999, 1), "unknown civilisation");
  }

-  test_request_set_government_rejects_when_unaffordable() {
+  test_request_set_government_goes_ahead_on_an_empty_treasury() {
    const state = smallState();
    state.budgets.set(0, 0);
-    this.assertFalse(state.requestSetGovernment(0, 1));
+    // The government can always pay, borrowing from the central bank.
+    this.assertTrue(state.requestSetGovernment(0, 1));
+    this.assertLess(state.getBudget(0), 0, "the adoption cost became debt");
  }

  test_government_effects_are_folded_into_gdp() {
    const state = smallState();
+    // Ports add a flat GDP that is not scaled by the government, so strip the
+    // seeded ones to keep the government multiplier the only variable.
+    stripPorts(state, 0);
    state.budgets.set(0, BIG_BUDGET);
    const monarchy = state.governments.findIndex((g) => g.id === "monarchy");
    const republicGdp = state.getPlayerGdp(0);
@@ -1,5 +1,5 @@
 import { TestCase } from "./framework/test_case.js";
-import { smallState } from "./framework/helpers.js";
+import { smallState, stripPorts } from "./framework/helpers.js";
 import { TECHNOLOGIES, EFFECT_INFANTRY_ATTACK, EFFECT_CONSTRUCTION_SPEED } from "../shared/data.js";
 import { NEWS_TECHNOLOGY } from "../shared/data/relations.js";

@@ -104,6 +104,7 @@ export class GameStateTechnologyTest extends TestCase {

  test_technology_effects_are_folded_into_gdp() {
    const state = smallState();
+    stripPorts(state, 0);
    const before = state.getPlayerGdp(0);
    this.complete(state, "scientific_method");
    this.assertApprox(state.getPlayerGdp(0), (before * 1.07) / 1.05, 0.01);
@@ -188,4 +189,11 @@ export class GameStateTechnologyTest extends TestCase {
      );
    }
  }
+
+  test_research_costs_a_hundred_times_the_catalogue_price() {
+    const state = smallState();
+    const index = this.index(state, "scientific_method");
+    const proto = TECHNOLOGIES[index];
+    this.assertEqual(state.getTechnologyCost(0, index), proto.cost * 100);
+  }
 }
@@ -119,7 +119,8 @@ export class GameStateTest extends TestCase {
    const state = smallState();
    this.assertGreater(state.getPlayerPopulation(0), 0);
    this.assertGreater(state.getPlayerGdp(0), 0);
-    this.assertGreater(state.getPlayerUpkeep(0), 0);
+    // Upkeep is now materials, not money: a starting army wears out steel.
+    this.assertGreater(state.getCivUpkeepResources(0).steel, 0);
    this.assertApprox(
      state.getBudget(0),
      state.getPlayerGdp(0) * ECONOMY.startingBudgetFraction,
@@ -128,7 +129,7 @@ export class GameStateTest extends TestCase {
    );
  }

-  test_civilisations_start_with_equal_cities_population_and_gdp_per_capita() {
+  test_civilisations_start_with_equal_cities_and_population() {
    const state = smallState(["france", "britain", "slovenia"]);
    const count = state.civilisations.length;
    const cities = [];
@@ -142,8 +143,14 @@ export class GameStateTest extends TestCase {
    }
    this.assertEqual(cities, [2, 2, 2], "every civ starts with the same number of cities");
    this.assertEqual(populations, [populations[0], populations[0], populations[0]], "every civ starts with the same population");
+    // GDP is the market value of what the land and its seeded works produce, so
+    // terrain makes it differ a little between nations; the balance keeps them
+    // within a narrow band rather than exactly equal.
    for (const perCapita of perCapitas) {
-      this.assertApprox(perCapita, perCapitas[0], 1e-6, "every civ starts with the same GDP per capita");
+      this.assertTrue(
+        Math.abs(perCapita - perCapitas[0]) <= perCapitas[0] * 0.15,
+        "every civ starts with a comparable GDP per capita"
+      );
    }
  }

@@ -4,36 +4,42 @@ import { ECONOMY } from "../shared/data.js";
 import { HOURS_PER_DAY } from "../shared/game_state/constants.js";
 import { parseKey } from "../shared/hex.js";

-// Natural GDP-per-capita growth: a constant daily amount measured from each
+// Natural production growth: a constant daily amount measured from each
 // tile's opening figure, so the relative growth rate tapers over the years.
 export class GdpGrowthTest extends TestCase {
  firstBaseline(state) {
-    const k = state.tileGdpBaseline.keys().next().value;
-    return { k, baseline: state.tileGdpBaseline.get(k), coords: parseKey(k) };
+    const k = state.tileProductionBaseline.keys().next().value;
+    return { k, baseline: state.tileProductionBaseline.get(k), coords: parseKey(k) };
  }

  test_a_day_adds_a_constant_share_of_the_opening_figure() {
    const state = smallState();
+    // Measure natural growth alone; migration would move people between regions
+    // and shift the per-capita on its own.
+    state._migrateForIncome = () => {};
    const { k, baseline, coords } = this.firstBaseline(state);
-    this.assertTrue(baseline > 0, "the tile has an opening GDP per capita");
+    this.assertTrue(baseline > 0, "the tile has an opening production per head");
    const opening = state.getTileGdpPerCapita(coords);
    this.assertApprox(opening, baseline, 1e-9, "day zero is the baseline");
    for (let i = 0; i < HOURS_PER_DAY; i++) state.tickHour();
    const dayOne = state.getTileGdpPerCapita(coords);
-    const step = baseline * ECONOMY.naturalGdpGrowthPerDay;
-    this.assertApprox(dayOne - opening, step, 1e-6, "one day adds one step");
-    // Thirty more days add exactly thirty more steps: the amount is constant.
+    const step = baseline * ECONOMY.naturalProductionGrowthPerDay;
+    this.assertTrue(dayOne > opening, "the tile has grown after a day");
+    // The total also tracks market prices, which drift as production meets
+    // demand; the natural-growth term itself is what adds exactly one step.
+    this.assertApprox(state._naturalTileProductionGrowth(k), step, 1e-6, "one day adds one step");
+    // Thirty more days add exactly thirty more steps: the natural-growth term is
+    // a constant. The tile's total also tracks production and market prices,
+    // which drift on their own, so the term itself is what stays linear.
    state.totalHours = 31 * HOURS_PER_DAY;
-    state._gdpPerCapitaCache.clear();
-    const dayThirtyOne = state.getTileGdpPerCapita(coords);
-    this.assertApprox(dayThirtyOne - dayOne, 30 * step, 1e-6, "the daily amount never grows");
-    this.assertEqual(k, state.tileGdpBaseline.keys().next().value, "the baseline never moves");
+    this.assertApprox(state._naturalTileProductionGrowth(k), 31 * step, 1e-6, "the daily amount never grows");
+    this.assertEqual(k, state.tileProductionBaseline.keys().next().value, "the baseline never moves");
  }

  test_the_relative_growth_rate_falls_as_the_tile_grows() {
    const state = smallState();
    const { baseline, coords } = this.firstBaseline(state);
-    const step = baseline * ECONOMY.naturalGdpGrowthPerDay;
+    const step = baseline * ECONOMY.naturalProductionGrowthPerDay;
    const earlyRate = step / baseline;
    state.totalHours = 366 * HOURS_PER_DAY;
    state._gdpPerCapitaCache.clear();
@@ -47,6 +53,8 @@ export class GdpGrowthTest extends TestCase {

  test_growth_is_measured_from_january_2000_in_the_first_year() {
    const state = smallState();
+    // Hold migration still so the day's change is natural growth alone.
+    state._migrateForIncome = () => {};
    const growth = state.viewerStats(0).growth;
    this.assertNotNull(growth, "the viewer carries growth figures");
    this.assertTrue(growth.sinceStart, "the first year measures from January 2000");
@@ -85,12 +93,12 @@ export class GdpGrowthTest extends TestCase {
    const state = smallState();
    const first = state.snapshot(0);
    this.assertSize(
-      first.gdpBaseline,
-      state.tileGdpBaseline.size,
+      first.productionBaseline,
+      state.tileProductionBaseline.size,
      "every baseline tile travels"
    );
    this.assertNotNull(first.viewerStats.growth, "the viewer's growth travels too");
    // The version never moves, so the delta wire drops the baseline afterwards.
-    this.assertEqual(first.versions.gdpBaseline, 0, "the baseline version is static");
+    this.assertEqual(first.versions.productionBaseline, 0, "the baseline version is static");
  }
 }
@@ -1,7 +1,9 @@
 import { TestCase } from "./framework/test_case.js";
 import { smallState, cityOf } from "./framework/helpers.js";
 import { key } from "../shared/hex.js";
-import { TRANSPORT_BY_ID } from "../shared/data/improvements.js";
+import { TRANSPORT_BY_ID, TILE_IMPROVEMENT_BY_ID } from "../shared/data/improvements.js";
+import { RESOURCE_RULES } from "../shared/data/resources.js";
+import { tileImprovementResourceCost } from "../shared/resources.js";

 const BIG_BUDGET = 10_000_000_000;

@@ -14,9 +16,14 @@ function bareOwnedLand(state, civ = 0) {
 }

 export class ImprovementsTest extends TestCase {
-  test_building_a_road_costs_money_and_lays_the_tile() {
+  test_building_a_road_costs_money_and_resources_and_lays_the_tile() {
    const state = smallState();
    state.budgets.set(0, BIG_BUDGET);
+    // Stock enough steel that only the electricity is bought on the market, so
+    // the money bill is the build cost plus the construction energy.
+    for (const city of state.cities) {
+      if (city.civ === 0) state.getCityResourceStock(city).steel = 1e9;
+    }
    const coords = bareOwnedLand(state);
    this.assertNotNull(coords, "the map has a bare owned land tile");
    const k = key(coords.x, coords.y);
@@ -24,7 +31,14 @@ export class ImprovementsTest extends TestCase {
    this.assertTrue(state.requestBuildImprovement(0, coords, "road"));
    this.assertTrue(state.roads.has(k), "the road is on the tile");
    this.assertFalse(state.railways.has(k), "it is not a railway");
-    this.assertApprox(before - state.getBudget(0), TRANSPORT_BY_ID.road.buildCost);
+    const materials = tileImprovementResourceCost(TRANSPORT_BY_ID.road);
+    const energyCost = materials.energy * state.getResourcePrice("energy");
+    this.assertApprox(
+      before - state.getBudget(0),
+      TRANSPORT_BY_ID.road.buildCost + energyCost,
+      1e-3,
+      "money plus the construction electricity"
+    );
  }

  test_a_railway_replaces_a_road_and_moves_twice_as_fast() {
@@ -95,12 +109,14 @@ export class ImprovementsTest extends TestCase {
    this.assertApprox(state.getBudget(0), after, 1e-9, "nothing was charged");
  }

-  test_poor_nations_cannot_build() {
+  test_a_road_can_be_built_on_an_empty_treasury() {
    const state = smallState();
    state.budgets.set(0, 0);
    const coords = bareOwnedLand(state);
-    this.assertFalse(state.requestBuildImprovement(0, coords, "road"));
-    this.assertFalse(state.roads.has(key(coords.x, coords.y)));
+    // The government can always pay, so the road goes ahead on borrowed money.
+    this.assertTrue(state.requestBuildImprovement(0, coords, "road"));
+    this.assertTrue(state.roads.has(key(coords.x, coords.y)));
+    this.assertLess(state.getBudget(0), 0, "the cost became central-bank debt");
  }

  test_maintenance_counts_roads_and_railways_the_nation_holds() {
@@ -112,16 +128,16 @@ export class ImprovementsTest extends TestCase {
    this.assertTrue(state.requestBuildImprovement(0, coords, "road"));
    this.assertApprox(
      state.getTransportUpkeep(0) - before,
-      TRANSPORT_BY_ID.road.maintenance,
+      RESOURCE_RULES.transportUpkeepSteel.road,
      1e-9,
-      "a road adds its hourly maintenance"
+      "a road adds its daily steel wear"
    );
    this.assertTrue(state.requestBuildImprovement(0, coords, "railway"));
    this.assertApprox(
      state.getTransportUpkeep(0) - before,
-      TRANSPORT_BY_ID.railway.maintenance,
+      RESOURCE_RULES.transportUpkeepSteel.railway,
      1e-9,
-      "the railway replaces the road's maintenance"
+      "the railway replaces the road's wear"
    );
  }

@@ -176,4 +192,37 @@ export class ImprovementsTest extends TestCase {
    this.assertTrue(state.railways.has(k), "a city carries a railway");
    this.assertFalse(state.roads.has(k), "not a road");
  }
+
+  test_a_tile_work_costs_steel_energy_and_high_tech() {
+    const state = smallState();
+    state.budgets.set(0, 1.0e15);
+    // Enough stores that only the electricity is bought, so the money bill is
+    // the build cost plus the construction energy.
+    for (const city of state.cities) {
+      if (city.civ !== 0) continue;
+      const stock = state.getCityResourceStock(city);
+      stock.steel = 1e9;
+      stock.hightech = 1e6;
+    }
+    const coords = state.landCells.find((cell) => {
+      const k = key(cell.x, cell.y);
+      return state.civAt(cell) === 0 && !state.cityAt(cell) && !state.tileImprovements.has(k);
+    });
+    this.assertNotNull(coords, "the player owns a bare land tile");
+    // A radar tower is advanced, so it also spends high-tech.
+    const radar = TILE_IMPROVEMENT_BY_ID.radar_tower;
+    const materials = tileImprovementResourceCost(radar);
+    this.assertGreater(materials.steel, 0, "steel is spent");
+    this.assertGreater(materials.energy, 0, "energy is spent");
+    this.assertGreater(materials.hightech, 0, "high-tech is spent");
+    const before = state.getBudget(0);
+    this.assertTrue(state.requestBuildTileImprovement(0, coords, "radar_tower"));
+    const energyCost = materials.energy * state.getResourcePrice("energy");
+    this.assertApprox(
+      before - state.getBudget(0),
+      radar.buildCost + energyCost,
+      1e-3,
+      "money plus the construction electricity"
+    );
+  }
 }
@@ -123,7 +123,7 @@ export class MapGeneratorTest extends TestCase {
      this.assertHas(tile, "terrainClass");
      this.assertHas(tile, "movementCostMultiplier");
      this.assertHas(tile, "populationMultiplier");
-      this.assertHas(tile, "gdpMultiplier");
+      this.assertHas(tile, "productionMultiplier");
    }
  }

@@ -98,8 +98,8 @@ export class MapModesTest extends TestCase {
      this.assertFalse(map.political, "the political fill is off");
      this.assertFalse(env.$("#map-legend").hasClass("hidden"), "the legend is shown");
      this.assertEqual(env.$("#map-legend-title").text(), "GDP per capita", "the legend is titled");
-      this.assertEqual(env.$("#map-legend-min").text(), "€100", "the legend shows the minimum");
-      this.assertEqual(env.$("#map-legend-max").text(), "€1 234", "the legend shows the maximum");
+      this.assertEqual(env.$("#map-legend-min").text(), "¤100", "the legend shows the minimum");
+      this.assertEqual(env.$("#map-legend-max").text(), "¤1 234", "the legend shows the maximum");
      // Every land tile carries the top-of-range colour, so the fill is live.
      const top = economicColour(1234, 100, 1234);
      let painted = false;
@@ -140,6 +140,25 @@ export class MapModesTest extends TestCase {
    }
  }

+  async test_the_delivery_graph_shows_only_in_economic_modes() {
+    const state = smallState();
+    const env = await setupDom();
+    const map = this.buildMap(env);
+    try {
+      map.applySnapshot(state.snapshot(0));
+      map.setMapMode("terrain");
+      map.setResourceGraph({ nodes: [[1, 1, 1]], links: [[0, 0, 1, 1, "steel", 10]] });
+      this.assertEmpty(env.$("#layer-resources .resource-node"), "hidden on the terrain map");
+      this.assertEmpty(env.$("#layer-resources .border-seg"), "and no delivery legs either");
+      map.setResourceGraph({ nodes: [[1, 1, 1]], links: [[0, 0, 1, 1, "steel", 10]] });
+      map.setMapMode("population");
+      this.assertNotEmpty(env.$("#layer-resources .resource-node"), "shown in an economic mode");
+      this.assertNotEmpty(env.$("#layer-resources .border-seg"), "the delivery leg is drawn");
+    } finally {
+      teardownDom(env);
+    }
+  }
+
  async test_fog_rebuilds_are_coalesced_between_frames() {
    const env = await setupDom();
    const map = this.buildMap(env);
@@ -12,8 +12,14 @@ export class MapViewTest extends TestCase {
    const map = new MapView(env.$("#map-viewport"), env.$("#map-world"), mapLayers(env.$));
    map.$viewport.width = () => 800;
    map.$viewport.height = () => 600;
-    map.setCatalogue(CIVILISATIONS, PROTO_UNITS);
    const snapshot = state.snapshot(0);
+    // The snapshot ships the nations in their seeded order; rebuild the full
+    // catalogue in that same order so owner indices line up, exactly as the
+    // game screen does.
+    const catalogue = snapshot.civs.map(
+      (c) => CIVILISATIONS.find((full) => full.id === c.id) || c
+    );
+    map.setCatalogue(catalogue, PROTO_UNITS);
    map.applySnapshot(snapshot);
    return { env, map, snapshot };
  }
@@ -127,13 +133,14 @@ export class MapViewTest extends TestCase {

  async test_unit_views_show_their_owners_flag() {
    const state = smallState();
-    const { env } = await this.build(state);
+    const { env, map } = await this.build(state);
    try {
      const flags = env.$("#layer-entities .unit .unit-flag");
      this.assertSize(flags, state.units.length, "every unit carries a flag");
      const unit = state.units[0];
      const civ = CIVILISATIONS.find((c) => c.id === state.civilisations[unit.civ].id);
-      const src = env.$("#layer-entities .unit").first().find(".unit-flag").attr("src") || "";
+      const view = map._unitViews.get(unit.id);
+      const src = (view && view.querySelector(".unit-flag").getAttribute("src")) || "";
      this.assertTrue(src.endsWith(civ.flag), `the flag is the owner's: ${src}`);
    } finally {
      teardownDom(env);
@@ -0,0 +1,109 @@
+import { TestCase } from "./framework/test_case.js";
+import { smallState, cityOf } from "./framework/helpers.js";
+import { key } from "../shared/hex.js";
+
+export class MigrationTest extends TestCase {
+  test_food_output_comes_from_the_land_not_the_headcount() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const before = state._regionProductionValue(city);
+    // Pack many more people onto the same land: the harvest must not change.
+    for (const coords of state.regionTiles(city)) {
+      const k = key(coords.x, coords.y);
+      state.tilePopulation.set(k, (state.tilePopulation.get(k) || 0) * 4 + 1);
+    }
+    state._gdpPerCapitaCache.clear();
+    const after = state._regionProductionValue(city);
+    this.assertApprox(after, before, 1e-6, "the land yields the same however many live on it");
+  }
+
+  test_regions_of_a_nation_open_with_equal_income_per_head() {
+    const state = smallState();
+    for (let civ = 0; civ < state.civilisations.length; civ++) {
+      const cities = state.cities.filter((city) => city.civ === civ);
+      if (cities.length < 2) continue;
+      const perHead = cities.map((city) => {
+        const economy = state.getCityEconomy(city);
+        return economy.population > 0 ? economy.gdp / economy.population : 0;
+      });
+      const highest = Math.max(...perHead);
+      const lowest = Math.min(...perHead);
+      this.assertTrue(
+        highest > 0 && (highest - lowest) / highest <= 0.02,
+        `regions of civ ${civ} open level`
+      );
+    }
+  }
+
+  test_moving_people_conserves_the_total() {
+    const state = smallState();
+    const cities = state.cities.filter((city) => city.civ === 0);
+    this.assertGreaterOrEqual(cities.length, 2, "the fixture has two regions");
+    const from = cities[0];
+    const to = cities[1];
+    const fromBefore = state.regionPopulation(from);
+    const toBefore = state.regionPopulation(to);
+    const moved = state._movePopulation(from, to, 100_000, false);
+    this.assertApprox(moved, 100_000, 1);
+    this.assertApprox(state.regionPopulation(from), fromBefore - moved, 1e-6);
+    this.assertApprox(state.regionPopulation(to), toBefore + moved, 1e-6);
+  }
+
+  test_people_move_toward_the_richer_region() {
+    const state = smallState();
+    const cities = state.cities.filter((city) => city.civ === 0);
+    const rich = cities[0];
+    const poor = cities[1];
+    // Dense on one side, sparse on the other: with land-based food that makes
+    // the sparse region the rich one.
+    for (const coords of state.regionTiles(rich)) {
+      state.tilePopulation.set(key(coords.x, coords.y), 1_000);
+    }
+    for (const coords of state.regionTiles(poor)) {
+      state.tilePopulation.set(key(coords.x, coords.y), 5_000_000);
+    }
+    state._gdpPerCapitaCache.clear();
+    const richBefore = state.regionPopulation(rich);
+    const poorBefore = state.regionPopulation(poor);
+    state._migrateForIncome();
+    this.assertGreater(state.regionPopulation(rich), richBefore, "people moved to the rich region");
+    this.assertLess(state.regionPopulation(poor), poorBefore, "and left the poor one");
+  }
+
+  test_a_region_only_moves_to_a_much_richer_one() {
+    const state = smallState();
+    // Migration levelled the regions at generation, so no one is twice as rich
+    // as anyone else and nobody moves.
+    const before = state.cities.map((city) => state.regionPopulation(city));
+    state._migrateForIncome();
+    const after = state.cities.map((city) => state.regionPopulation(city));
+    for (let i = 0; i < before.length; i++) {
+      this.assertApprox(after[i], before[i], 1e-6, "nobody moved to a merely equal region");
+    }
+  }
+
+  test_an_airport_caps_its_daily_intake() {
+    const state = smallState();
+    const cities = state.cities;
+    const from = cityOf(state, 0);
+    const to = cities.find((city) => city.civ === 1);
+    // Every region is dense and equally poor except `to`, which is sparse and
+    // so far richer. Only `to` is worth moving to.
+    for (const city of cities) {
+      const people = city.id === to.id ? 1_000 : 5_000_000;
+      for (const coords of state.regionTiles(city)) {
+        state.tilePopulation.set(key(coords.x, coords.y), people);
+      }
+    }
+    state._gdpPerCapitaCache.clear();
+    const airport = state.protoBuildings.findIndex((b) => b.id === "airport");
+    from.buildings[airport] = 1;
+    to.buildings[airport] = 1;
+    const fromBefore = state.regionPopulation(from);
+    state._migrateForIncome();
+    const lost = fromBefore - state.regionPopulation(from);
+    this.assertGreater(lost, 0, "people flew to the rich region");
+    // 1000 people per airport level a day, and the route's level is 1.
+    this.assertTrue(lost <= 1_001, `the flight carried at most its capacity, lost ${lost}`);
+  }
+}
@@ -2,7 +2,8 @@ import { TestCase } from "./framework/test_case.js";
 import { setupDom, teardownDom } from "./framework/dom.js";
 import { CityModal, NationModal, ConfirmModal, NewsModal } from "../client/js/modals.js";
 import { buildingEffectText, describeNews } from "../client/js/modals/format.js";
-import { BUILDINGS, GOVERNMENTS, TECHNOLOGIES, PROTO_UNITS } from "../shared/data.js";
+import { BUILDINGS, GOVERNMENTS, TECHNOLOGIES, PROTO_UNITS, technologyCost } from "../shared/data.js";
+import { groupDigits } from "../shared/text_format.js";

 export class CityModalTest extends TestCase {
  test_utility_buildings_describe_their_mechanic() {
@@ -14,7 +15,7 @@ export class CityModalTest extends TestCase {
    const shelters = BUILDINGS.find((b) => b.id === "shelters");
    this.assertTrue(buildingEffectText(shelters, 2).includes("20%"), "the shelters show their protection");
    const market = BUILDINGS.find((b) => b.id === "market");
-    this.assertTrue(buildingEffectText(market, 1).includes("GDP/capita"), "stats keep their effect text");
+    this.assertTrue(buildingEffectText(market, 1).includes("production"), "stats keep their effect text");
  }
  showTrain(modal, queue = []) {
    modal.show(
@@ -165,13 +166,15 @@ export class CityModalTest extends TestCase {
    }
  }

-  async test_unaffordable_upgrade_is_disabled() {
+  async test_upgrade_stays_available_on_an_empty_treasury() {
    const env = await setupDom();
    try {
      const modal = new CityModal();
      modal.show({ id: 1, name: "X" }, { budget: 0, buildings: BUILDINGS, levels: {} });
      const upgrade = env.$("#city-buildings-list .row-card").first().find(".actions button").first();
-      this.assertTrue(upgrade.prop("disabled"));
+      // The government can always pay, running an overdraft, so cost never
+      // disables the button; only an unmet requirement does.
+      this.assertFalse(upgrade.prop("disabled"));
    } finally {
      teardownDom(env);
    }
@@ -208,13 +211,13 @@ export class CityModalTest extends TestCase {
      };
      modal.show({ id: 1, name: "Paris" }, { budget: 1.0e15, buildings: BUILDINGS, levels: {} });
      modal.renderBudget(breakdown);
-      this.assertTrue(env.$("#city-budget-sub").text().includes("+€635/h"), "the region net is shown");
+      this.assertTrue(env.$("#city-budget-sub").text().includes("+¤635/h"), "the region net is shown");
      const text = env.$("#city-budget-list").text();
-      this.assertTrue(text.includes("+€1 035/h"), "region tax income is green");
+      this.assertTrue(text.includes("+¤1 035/h"), "region tax income is green");
      this.assertTrue(text.includes("Bank in Paris (building) +5.0%"), "a building bonus is listed");
-      this.assertTrue(text.includes("−€400/h"), "the building upkeep is listed");
+      this.assertTrue(text.includes("−¤400/h"), "the building upkeep is listed");
      this.assertTrue(text.includes("TOTAL"), "a total row is present");
-      this.assertTrue(text.includes("+€635/h"), "the total carries the region net");
+      this.assertTrue(text.includes("+¤635/h"), "the total carries the region net");
      this.assertFalse(text.includes("No units"), "unit upkeep is national, not regional");

      env.$("#city-budget-list tr.budget-group .budget-name").click();
@@ -244,6 +247,36 @@ export class CityModalTest extends TestCase {
      teardownDom(env);
    }
  }
+
+  async test_economy_tab_shows_the_regions_cash_basket() {
+    const env = await setupDom();
+    try {
+      const modal = new CityModal();
+      modal.show(
+        { id: 1, name: "Lyon" },
+        {
+          budget: 1.0e9,
+          gdp: 1.0e9,
+          cash: { FRF: 4000, GBP: 250 },
+          cashValue: 4250,
+          debt: 250,
+          currencies: [
+            { code: "FRF", symbol: "₣", name: "French Franc" },
+            { code: "GBP", symbol: "£", name: "British Pound" },
+          ],
+        }
+      );
+      env.$("#modal-city .tab[data-tab=economy]").click();
+      this.assertTrue(env.$("#city-tab-economy").hasClass("active"));
+      const text = env.$("#city-economy-list").text();
+      this.assertTrue(text.includes("French Franc"), "the national currency is listed");
+      this.assertTrue(text.includes("British Pound"), "a foreign holding is listed");
+      this.assertTrue(env.$("#city-economy-sub").text().includes("4 250"), "the total value shows");
+      this.assertTrue(env.$("#city-economy-sub").text().includes("Debt"), "the central-bank debt shows");
+    } finally {
+      teardownDom(env);
+    }
+  }
 }

 export class NationModalTest extends TestCase {
@@ -334,6 +367,90 @@ export class NationModalTest extends TestCase {
    }
  }

+  async test_resources_tab_lists_stores_needs_and_the_market() {
+    const env = await setupDom();
+    try {
+      const modal = new NationModal();
+      const summary = {
+        stock: { steel: 1000, food: 2_000_000, luxury: 5000, hightech: 12 },
+        need: { steel: 10, food: 20, luxury: 30, hightech: 0 },
+        production: { steel: 5, food: 0, luxury: 0, hightech: 1 },
+        consumed: { steel: 15, food: 25, luxury: 35, hightech: 2, energy: 1.1e9 },
+        energy: { need: 1.0e9, supply: 2.0e9 },
+        trade: { imports: { steel: 40 }, exports: { steel: 7 } },
+        prices: {},
+      };
+      const market = [
+        { id: "energy", price: 0.003, supply: 1.0e9, demand: 2.0e9 },
+        { id: "steel", price: 600, supply: 100, demand: 200 },
+        { id: "food", price: 300, supply: 50, demand: 60 },
+        { id: "luxury", price: 60, supply: 0, demand: 10 },
+        { id: "hightech", price: 800, supply: 0, demand: 0 },
+      ];
+      modal.show(
+        GOVERNMENTS, 0, TECHNOLOGIES, new Set(), 1.0e9, 1.0e15, 5,
+        {}, null, [], null, null, { summary, market }
+      );
+      env.$("#modal-nation .tab[data-tab=resources]").click();
+      this.assertTrue(env.$("#tab-resources").hasClass("active"), "the tab opens");
+      const rows = env.$("#resources-list .resources-table tbody tr");
+      this.assertSize(rows, 5, "one row for every resource");
+      const energy = rows.eq(0);
+      this.assertTrue(energy.find(".name").text().includes("Energy"), "energy leads the list");
+      this.assertEqual(energy.find("td").eq(1).text(), "—", "energy has no store");
+      const steel = rows.eq(1);
+      this.assertTrue(steel.find(".name").text().includes("Steel"));
+      this.assertTrue(steel.find("td").eq(2).text().includes("15"), "consumption is shown");
+      this.assertTrue(steel.find("td").eq(4).text().includes("7"), "exports are shown");
+      this.assertTrue(steel.find("td").eq(5).text().includes("40"), "imports are shown");
+      this.assertTrue(steel.find("td").eq(6).text().includes("600"), "the steel price is shown");
+      this.assertTrue(steel.find("td").eq(7).text().length > 0, "world supply is shown");
+      modal.refresh(
+        0, new Set(), 1.0e9, 1.0e15, 5, {}, null, null, null, null,
+        { summary, market }
+      );
+      this.assertSize(env.$("#resources-list .resources-table tbody tr"), 5, "refreshing keeps the rows");
+      modal.close();
+    } finally {
+      teardownDom(env);
+    }
+  }
+
+  async test_resources_tab_ranks_major_exporters_and_importers() {
+    const env = await setupDom();
+    try {
+      const modal = new NationModal();
+      const summary = {
+        stock: { steel: 0, food: 0, luxury: 0, hightech: 0 },
+        need: { steel: 0, food: 0, luxury: 0, hightech: 0 },
+        production: { steel: 0, food: 0, luxury: 0, hightech: 0 },
+        consumed: { steel: 0, food: 0, luxury: 0, hightech: 0, energy: 0 },
+        energy: { need: 0, supply: 0 },
+        trade: { imports: {}, exports: {} },
+        prices: {},
+      };
+      const trade = [
+        { civ: 0, imports: { steel: 10 }, exports: { steel: 100 } },
+        { civ: 1, imports: { steel: 50 }, exports: { steel: 5 } },
+      ];
+      const civs = [{ name: "France" }, { name: "Britain" }];
+      modal.show(
+        GOVERNMENTS, 0, TECHNOLOGIES, new Set(), 1.0e9, 1.0e15, 5,
+        {}, null, [], null, null, { summary, market: [], trade, civs }
+      );
+      env.$("#modal-nation .tab[data-tab=resources]").click();
+      env.$("#resources-subtabs .subtab[data-view=leaders]").click();
+      const rows = env.$("#resource-trade-list .resources-table tbody tr");
+      this.assertSize(rows, 5, "one row for every resource");
+      const steel = rows.eq(1);
+      this.assertTrue(steel.find("td").eq(1).text().includes("France"), "the major exporter leads");
+      this.assertTrue(steel.find("td").eq(3).text().includes("Britain"), "the major importer leads");
+      modal.close();
+    } finally {
+      teardownDom(env);
+    }
+  }
+
  async test_a_focused_technology_shows_a_progress_bar() {
    const env = await setupDom();
    try {
@@ -346,7 +463,11 @@ export class NationModalTest extends TestCase {
      });
      const card = env.$("#technology-list .row-card").eq(method);
      this.assertTrue(card.find(".tech-progress-track").length > 0, "the focus has a bar");
-      this.assertEqual(card.find(".tech-progress-text").text(), "10 / 20", "X / Y beside it");
+      this.assertEqual(
+        card.find(".tech-progress-text").text(),
+        `10 / ${groupDigits(technologyCost(TECHNOLOGIES[method]))}`,
+        "X / Y beside it"
+      );
      this.assertEqual(card.find(".actions button").text(), "Focused", "no cost on the button");
      modal.close();
    } finally {
@@ -393,38 +514,49 @@ export class NationModalTest extends TestCase {
    }
  }

-  async test_budget_tab_shows_income_and_upkeep_breakdown() {
+  async test_budget_tab_shows_monthly_income_and_expenses() {
    const env = await setupDom();
    try {
      const modal = new NationModal();
+      const month = (overrides) => ({
+        monthIndex: 24000,
+        isCurrent: true,
+        label: "January 2000",
+        income: 0,
+        sales: 0,
+        totalCash: 0,
+        totalEconomic: 0,
+        net: 0,
+        expenses: [],
+        resourceTrade: [],
+        ...overrides,
+      });
      const finances = {
-        income: {
-          rate: 0.001,
-          base: 900,
-          modifier: 0.15,
-          total: 1035,
-          sources: [
-            { label: "Bank", kind: "building", effect: 0.05, amount: 45, cityId: 1, cityName: "Paris" },
-            { label: "Republic", kind: "government", effect: 0.1, amount: 90 },
-          ],
-        },
-        buildingUpkeep: {
-          total: 400,
-          sources: [{ label: "Bank", kind: "building", amount: 400 }],
-          groups: [
-            {
-              index: 1,
-              label: "Bank",
-              amount: 400,
-              cities: [{ cityId: 1, cityName: "Paris", level: 2, amount: 400 }],
-            },
-          ],
-        },
-        unitUpkeep: {
-          total: 150,
-          sources: [{ label: "Modern infantry", kind: "unit", amount: 150, count: 3 }],
-        },
-        net: 485,
+        months: [
+          month({
+            monthIndex: 23999,
+            isCurrent: false,
+            label: "December 1999",
+            income: 500,
+            totalCash: 400,
+            totalEconomic: 1200,
+            net: 100,
+            expenses: [["buildings", 400, 1200]],
+          }),
+          month({
+            income: 1035,
+            sales: 60,
+            totalCash: 550,
+            totalEconomic: 900,
+            net: 545,
+            expenses: [
+              ["buildings", 400, 700, [["steel", 250], ["hightech", 150]]],
+              ["units", 150, 200, []],
+            ],
+            resourceTrade: [["steel", 220, 0], ["food", 0, 90]],
+          }),
+        ],
+        cities: [],
      };
      modal.show(GOVERNMENTS, 0, TECHNOLOGIES, new Set(), 1.0e9, 1.0e15, 1.0e6, finances);
      env.$("#modal-nation .tab[data-tab=budget]").click();
@@ -432,31 +564,44 @@ export class NationModalTest extends TestCase {
      this.assertSize(env.$("#budget-list table.budget-table"), 1);

      const text = env.$("#budget-list").text();
-      this.assertTrue(text.includes("+€1 035/h"), "tax income is green");
-      this.assertTrue(text.includes("Bank in Paris (building) +5.0%"), "a building bonus is listed");
-      this.assertTrue(text.includes("Republic (government) +10.0%"), "a government bonus is listed");
-      this.assertTrue(text.includes("−€400/h"), "the building group shows its total cost");
-      this.assertTrue(text.includes("Modern infantry ×3"), "unit upkeep is listed");
+      this.assertTrue(text.includes("+¤1 035"), "the month's tax income is shown");
+      this.assertTrue(text.includes("Resource sales"), "resource sales are shown");
+      this.assertTrue(text.includes("Building upkeep"), "a building category is listed");
+      this.assertTrue(text.includes("−¤400"), "the building cash is listed");
+      this.assertTrue(text.includes("materials valued at ¤700"), "the market value is noted");
+      this.assertTrue(text.includes("Unit upkeep"), "a unit category is listed");
+      this.assertTrue(text.includes("Bought Steel"), "a bought resource is listed");
+      this.assertTrue(text.includes("Sold Food"), "a sold resource is listed");
      this.assertTrue(text.includes("TOTAL"), "a total row is present");
-      this.assertTrue(text.includes("+€485/h"), "the total carries the net balance");
+      this.assertTrue(text.includes("+¤545"), "the total carries the month net");
      this.assertTrue(env.$("#budget-sub").text().includes("Treasury"));
+      this.assertTrue(env.$("#budget-sub").text().includes("January 2000"), "the month is named");

-      // Expanding the building type reveals the per-city cost.
-      env.$("#budget-list tr.budget-group .budget-name").click();
+      // Expanding an upkeep row names the resources it bought.
+      env.$("#budget-list tr .budget-name.clickable").first().click();
+      const expanded = env.$("#budget-list").text();
+      this.assertTrue(expanded.includes("Steel"), "the expanded row names steel");
+      this.assertTrue(expanded.includes("−¤250"), "and what it paid for it");
+
+      // The pager steps back to the previous month's digest.
+      env.$("#budget-months .budget-month-nav").first().click();
      this.assertTrue(
-        env.$("#budget-list").text().includes("Bank in Paris — level 2"),
-        "expanding a building type shows its cities"
+        env.$("#budget-sub").text().includes("December 1999"),
+        "the pager names the older month"
      );

      modal.refresh(0, new Set(), 1.0e9, 1.0e15, 1.0e6, {
-        income: { rate: 0.001, base: 100, modifier: 0, total: 100, sources: [] },
-        buildingUpkeep: { total: 400, sources: [], groups: [] },
-        unitUpkeep: { total: 150, sources: [], groups: [] },
-        net: -450,
+        months: [month({
+          income: 100,
+          totalCash: 400,
+          totalEconomic: 400,
+          net: -300,
+          expenses: [["buildings", 400, 400]],
+        })],
+        cities: [],
      });
      const refreshed = env.$("#budget-list").text();
-      this.assertTrue(refreshed.includes("−€450/h"), "the total updates");
-      this.assertTrue(refreshed.includes("No bonuses"), "empty income sources are named");
+      this.assertTrue(refreshed.includes("−¤300"), "the total updates");
    } finally {
      teardownDom(env);
    }
@@ -522,8 +667,8 @@ export class NationModalTest extends TestCase {
      this.assertTrue(rows.eq(0).find(".name").text() === "Britain", "alphabetical by default");
      this.assertTrue(rows.eq(0).find(".status").text().includes("At peace"));
      const numbers = rows.eq(0).find("td.numeric");
-      this.assertTrue(numbers.eq(0).text().includes("€3B"), "Britain's GDP shows");
-      this.assertTrue(numbers.eq(1).text().includes("€2K"), "Britain's GDP/capita shows");
+      this.assertTrue(numbers.eq(0).text().includes("¤3B"), "Britain's GDP shows");
+      this.assertTrue(numbers.eq(1).text().includes("¤2K"), "Britain's GDP/capita shows");
      this.assertTrue(numbers.eq(2).text().includes("1.5M"), "Britain's population shows");

      const own = rows.eq(1);
@@ -586,6 +731,54 @@ export class NationModalTest extends TestCase {
      teardownDom(env);
    }
  }
+
+  async test_economy_tab_shows_private_cash_central_bank_and_rates() {
+    const env = await setupDom();
+    try {
+      const modal = new NationModal();
+      const money = {
+        viewerCiv: 0,
+        currency: { code: "FRF", symbol: "₣", name: "French Franc" },
+        currencies: [
+          { civ: 0, code: "FRF", symbol: "₣", name: "French Franc", value: 1 },
+          { civ: 1, code: "GBP", symbol: "£", name: "British Pound", value: 1 },
+        ],
+        exchangeRates: [
+          { civ: 0, code: "FRF", symbol: "₣", name: "French Franc", rate: 1 },
+          { civ: 1, code: "GBP", symbol: "£", name: "British Pound", rate: 0.85 },
+        ],
+        centralBank: {
+          rate: 0.02,
+          currency: { code: "FRF", symbol: "₣", name: "French Franc" },
+          reserves: [{ code: "GBP", symbol: "£", name: "British Pound", amount: 1234 }],
+          loans: 987654,
+        },
+        privateCash: 5000,
+        cities: [{ id: 1, civ: 0, name: "Paris", cashValue: 5000 }],
+      };
+      modal.show(
+        GOVERNMENTS, 0, TECHNOLOGIES, new Set(), 1.0e9, 1.0e15, 1.0e6,
+        { months: [], cities: [] }, null, [], null, null, null, money
+      );
+      env.$("#modal-nation .tab[data-tab=economy]").click();
+      this.assertTrue(env.$("#tab-economy").hasClass("active"));
+      const summary = env.$("#economy-summary").text();
+      this.assertTrue(summary.includes("Paris"), "the region is listed");
+      this.assertTrue(summary.includes("5 000"), "its private cash is shown");
+
+      env.$("#economy-subtabs .subtab[data-view=centralbank]").click();
+      const bank = env.$("#economy-central-bank").text();
+      this.assertTrue(bank.includes("British Pound"), "the foreign reserve is listed");
+      this.assertTrue(bank.includes("987 654"), "the outstanding loans are listed");
+      this.assertTrue(env.$("#cb-rate").length === 1, "the rate input is present");
+
+      env.$("#economy-subtabs .subtab[data-view=rates]").click();
+      this.assertTrue(env.$("#economy-rates").text().includes("British Pound"), "the rate table shows");
+      this.assertTrue(env.$("#economy-rates").text().includes("0.8500"), "the rate is shown");
+    } finally {
+      teardownDom(env);
+    }
+  }
 }

 export class ConfirmModalTest extends TestCase {
@@ -0,0 +1,269 @@
+import { TestCase } from "./framework/test_case.js";
+import { smallState, cityOf } from "./framework/helpers.js";
+import { HOURS_PER_DAY } from "../shared/game_state/constants.js";
+import { MONEY } from "../shared/data/economy.js";
+
+export class MoneyTest extends TestCase {
+  // The money in the world: treasuries, region baskets and bank reserves, less
+  // every debt owed to a bank. Rates are frozen by the caller so revaluation
+  // does not move the measure.
+  totalMoney(state) {
+    let total = 0;
+    for (let civ = 0; civ < state.civilisations.length; civ++) {
+      total += state.getBudget(civ);
+      for (const city of state.cities) {
+        if (city.civ !== civ) continue;
+        total -= state.getRegionDebt(city);
+      }
+      for (const [, amount] of state.getCentralBankDebt(civ)) total -= amount;
+    }
+    for (const city of state.cities) {
+      for (const [, amount] of state.getRegionCash(city)) total += amount;
+    }
+    for (const reserves of state.centralBankReserves.values()) {
+      for (const [, amount] of reserves) total += amount;
+    }
+    return total;
+  }
+
+  test_government_spending_is_paid_into_the_regions() {
+    const state = smallState();
+    const code = state.currencyOf(0).code;
+    const cities = state.cities.filter((city) => city.civ === 0);
+    const before = cities.map((city) => state.getRegionCash(city).get(code) || 0);
+    const budgetBefore = state.getBudget(0);
+    state._spendBudget(0, 1_000_000);
+    const after = cities.map((city) => state.getRegionCash(city).get(code) || 0);
+    const reached = after.reduce((sum, value, index) => sum + value - before[index], 0);
+    this.assertApprox(reached, 1_000_000, 1, "the money reached the private sector");
+    this.assertApprox(state.getBudget(0), budgetBefore - 1_000_000, 1e-6);
+  }
+
+  test_taxes_are_taken_from_the_regions() {
+    const state = smallState();
+    const code = state.currencyOf(0).code;
+    const cities = state.cities.filter((city) => city.civ === 0);
+    const holding = () => cities.reduce(
+      (sum, city) => sum + (state.getRegionCash(city).get(code) || 0), 0
+    );
+    const before = holding();
+    state._chargeRegions(0, 500_000);
+    this.assertApprox(before - holding(), 500_000, 1, "the tax came out of the regions");
+  }
+
+  test_a_spend_neither_creates_nor_destroys_money() {
+    const state = smallState();
+    // Hold the exchange rates still so the measure reads units, not revaluation.
+    state.setCurrencyValue = () => {};
+    const before = this.totalMoney(state);
+    state._spendBudget(0, 5_000_000, "training");
+    this.assertApprox(this.totalMoney(state), before, 1, "the spend moved money, it did not mint it");
+  }
+
+  test_a_market_purchase_neither_creates_nor_destroys_money() {
+    const state = smallState();
+    state.setCurrencyValue = () => {};
+    const city = cityOf(state, 0);
+    const before = this.totalMoney(state);
+    state._chargeRegionCash(city, state.currencyOf(0).code, 2_000_000);
+    state._payWorld(0, 2_000_000, state.currencyOf(0).code);
+    this.assertApprox(this.totalMoney(state), before, 1, "the import stayed in the world");
+  }
+
+  test_every_civilisation_has_a_currency() {
+    const state = smallState();
+    const codes = new Set();
+    for (let civ = 0; civ < state.civilisations.length; civ++) {
+      const currency = state.currencyOf(civ);
+      this.assertTrue(currency.name, "the currency is named");
+      this.assertTrue(currency.code, "the currency has a code");
+      this.assertTrue(currency.symbol, "the currency has a symbol");
+      codes.add(currency.code);
+    }
+    this.assertEqual(codes.size, state.civilisations.length, "codes are unique");
+  }
+
+  test_regions_open_with_private_cash_in_their_own_currency() {
+    const state = smallState();
+    for (const city of state.cities) {
+      const basket = state.getRegionCash(city);
+      this.assertSize(basket, 1, "a region opens holding one currency");
+      const code = state.currencyOf(city.civ).code;
+      this.assertTrue((basket.get(code) || 0) > 0, "its own national currency");
+      this.assertGreater(state.getRegionCashValue(city), 0, "the reserve has value");
+    }
+  }
+
+  test_a_short_region_borrows_from_the_central_bank() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const code = state.currencyOf(0).code;
+    state.getRegionCash(city).set(code, 0);
+    state._chargeRegionCash(city, code, 500);
+    this.assertApprox(state.getRegionDebt(city), 500, 1e-6, "the shortfall became debt");
+  }
+
+  test_region_debt_accrues_interest_daily() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    // No cash to repay with, so the debt compounds.
+    state.getRegionCash(city).set(state.currencyOf(0).code, 0);
+    state.regionDebt.set(city.id, 1000);
+    state._tickMoney();
+    this.assertApprox(
+      state.getRegionDebt(city), 1000 * (1 + MONEY.defaultInterestRate / 365), 1e-6
+    );
+  }
+
+  test_setting_the_rate_changes_the_debt_interest() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    this.assertTrue(state.requestSetInterestRate(0, 0.1));
+    state.getRegionCash(city).set(state.currencyOf(0).code, 0);
+    state.regionDebt.set(city.id, 1000);
+    state._tickMoney();
+    this.assertApprox(state.getRegionDebt(city), 1000 * (1 + 0.1 / 365), 1e-6);
+  }
+
+  test_the_government_can_run_an_overdraft() {
+    const state = smallState();
+    state.budgets.set(0, 100);
+    this.assertTrue(state._spendBudget(0, 1000, "training"), "a spend is never refused");
+    this.assertLess(state.getBudget(0), 0, "the treasury went into the red");
+    this.assertApprox(state.getGovernmentDebt(0), -state.getBudget(0), 1e-6);
+  }
+
+  test_the_rate_is_clamped_and_rejects_nonsense() {
+    const state = smallState();
+    state.requestSetInterestRate(0, 5);
+    this.assertEqual(state.getCentralBankRate(0), MONEY.maxInterestRate, "clamped to the ceiling");
+    this.assertFalse(state.requestSetInterestRate(0, -1), "a negative rate is refused");
+    this.assertFalse(state.requestSetInterestRate(99, 0.02), "an unknown nation is refused");
+  }
+
+  test_the_private_sector_aggregates_its_regions() {
+    const state = smallState();
+    let sum = 0;
+    for (const city of state.cities) {
+      if (city.civ !== 0) continue;
+      sum += state.getRegionCashValue(city);
+    }
+    this.assertApprox(state.getPrivateSectorCash(0), sum, 1e-6);
+  }
+
+  test_exchange_rates_follow_the_currency_values() {
+    const state = smallState();
+    this.assertApprox(state.exchangeRate(0, 1), 1, 1e-9, "currencies start at par");
+    state.setCurrencyValue(1, 0.5);
+    this.assertApprox(state.exchangeRate(0, 1), 2, 1e-9, "a cheaper currency buys fewer");
+  }
+
+  test_cross_border_trade_settles_through_the_central_bank() {
+    const state = smallState();
+    const buyer = cityOf(state, 0);
+    const seller = cityOf(state, 1);
+    state.getCityResourceStock(seller).food = 1e9;
+    state.getCityResourceStock(buyer).food = 0;
+    const buyerCode = state.currencyOf(0).code;
+    const sellerCode = state.currencyOf(1).code;
+    const buyerBefore = state.getRegionCash(buyer).get(buyerCode) || 0;
+    const sellerBefore = state.getRegionCash(seller).get(sellerCode) || 0;
+    const bought = state._procureFromNeighbours(
+      buyer, "food", 1000, state.getCityResourceStock(buyer), state._resourceNodes()
+    );
+    this.assertGreater(bought, 0, "the foreign neighbour sold food");
+    this.assertLess(
+      state.getRegionCash(buyer).get(buyerCode) || 0, buyerBefore, "the buyer spent its own currency"
+    );
+    this.assertGreater(
+      state.getRegionCash(seller).get(sellerCode) || 0,
+      sellerBefore,
+      "the seller was paid in its own currency"
+    );
+    this.assertGreater(
+      state.getCentralBankReserves(1).get(buyerCode) || 0,
+      0,
+      "the seller's central bank kept the buyer's currency as a reserve"
+    );
+  }
+
+  test_a_currency_in_demand_strengthens() {
+    const state = smallState();
+    const before = state.currencyValue(0);
+    state._recordCurrencyDemand(0, 1e12);
+    state._tickMoney();
+    this.assertGreater(state.currencyValue(0), before, "net demand lifts the rate");
+  }
+
+  test_regions_repatriate_foreign_cash() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const national = state.currencyOf(0).code;
+    const foreign = state.currencyOf(1).code;
+    const basket = state.getRegionCash(city);
+    basket.set(foreign, 1000);
+    const nationalBefore = basket.get(national) || 0;
+    state._tickMoney();
+    this.assertLess(basket.get(foreign) || 0, 1000, "the foreign holding shrank");
+    this.assertGreater(basket.get(national) || 0, nationalBefore, "national cash grew");
+  }
+
+  test_a_broke_region_buys_by_borrowing() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const portIndex = state.protoBuildings.findIndex((b) => b.id === "port");
+    const coastal = state.cities.find((c) => c.civ === 0 && state.isCoastalCity(c));
+    if (!coastal) return;
+    coastal.buildings[portIndex] = 1;
+    this.assertTrue(state._civMarketAccess(0), "a port opens the market");
+    state.getRegionCash(city).set(state.currencyOf(0).code, 0);
+    const store = state.getCityResourceStock(city);
+    const bought = state._buyMarketMaterial(city, "food", 100, store);
+    this.assertGreater(bought, 0, "the purchase still goes through");
+    this.assertGreater(state.getRegionDebt(city), 0, "it was funded by borrowing");
+  }
+
+  test_a_contested_surplus_is_bid_up() {
+    const state = smallState();
+    const buyer = cityOf(state, 0);
+    const nodes = state._resourceNodes();
+    const supplier = state._nearbySuppliers(buyer, "food", nodes)[0];
+    this.assertNotNull(supplier, "a supplier is reachable");
+    // Give that one node a huge surplus and drain every other store of food.
+    for (const [, stock] of state.resourceStock) stock.food = 0;
+    supplier.stock.food = 1e9;
+    state.getCityResourceStock(buyer).food = 0;
+    const receiverCity = supplier.city
+      || state._regionCityNear(supplier.civ, supplier.coords);
+    const code = state.currencyOf(supplier.civ).code;
+    const vSeller = state.currencyValue(supplier.civ);
+    // Pretend another buyer already claimed most of the surplus.
+    const surplus = state._nodeSurplus(supplier, "food");
+    state._nodeClaims = new Map([
+      [`${supplier.coords.x},${supplier.coords.y}`, surplus * 0.9],
+    ]);
+    const before = state.getRegionCash(receiverCity).get(code) || 0;
+    const store = state.getCityResourceStock(buyer);
+    const bought = state._procureFromNeighbours(
+      buyer, "food", 1000, store, state._resourceNodes()
+    );
+    this.assertGreater(bought, 0, "food still changes hands");
+    const paid = (state.getRegionCash(receiverCity).get(code) || 0) - before;
+    const barePrice = (bought * state.getResourcePrice("food")) / vSeller;
+    this.assertGreater(paid, barePrice, "the contested surplus fetched a premium");
+  }
+
+  test_the_snapshot_ships_the_money_view() {
+    const state = smallState();
+    const stats = state.snapshot(0).viewerStats;
+    this.assertTrue(stats.currency && stats.currency.code, "the viewer's currency travels");
+    this.assertSize(stats.currencies, state.civilisations.length, "every currency travels");
+    this.assertSize(stats.exchangeRates, state.civilisations.length, "every rate travels");
+    this.assertTrue(stats.centralBank, "the central bank travels");
+    this.assertApprox(stats.centralBank.rate, MONEY.defaultInterestRate, 1e-9);
+    this.assertGreater(stats.privateCash, 0, "the private-sector total travels");
+    const city = state.snapshot(0).cityStats[0];
+    this.assertNotNull(city.cash, "a region's cash basket travels");
+    this.assertGreater(city.cashValue, 0, "and its value");
+  }
+}
@@ -365,6 +365,14 @@ export class PoliticsModelTest extends TestCase {

  test_cultural_impact_is_zero_sum_and_wins_friends() {
    const state = smallState();
+    // Funded treasuries and private-sector cash, so the test measures culture
+    // alone: a nation short of either runs a resource shortage, whose popularity
+    // hit drowns out the museum.
+    state.budgets.set(0, 1e15);
+    state.budgets.set(1, 1e15);
+    for (const city of state.cities) {
+      state.getRegionCash(city).set(state.currencyOf(city.civ).code, 1e15);
+    }
    const museum = BUILDINGS.findIndex((b) => b.id === "museum");
    const city = state.cities.find((c) => c.civ === 0);
    city.buildings[museum] = 1;
@@ -138,13 +138,13 @@ export class EconomyOrderEdgesTest extends TestCase {
  test_battle_triples_unit_upkeep() {
    const state = smallState();
    const pair = boundaryLand(state);
-    const before = state.getPlayerUpkeep(0);
+    const before = state.getCivUpkeepResources(0).steel;
    state._spawnUnit(pair.a, 0, state.protoUnits[0]);
    state._spawnUnit(pair.b, 1, state.protoUnits[0]);
    // The two hostile units are only "in battle" once they share a tile.
    state.units[state.units.length - 1].coords = pair.a;
-    const after = state.getPlayerUpkeep(0);
-    this.assertGreater(after, before, "a unit in battle costs more to keep");
+    const after = state.getCivUpkeepResources(0).steel;
+    this.assertGreater(after, before, "a unit in battle burns more steel");
  }

  test_buildings_in_the_catalogue_have_a_cost_curve() {
@@ -208,7 +208,7 @@ export class CatalogueSplitTest extends TestCase {
  test_pillaging_with_no_units_changes_nothing() {
    const result = pillageSteps(5000, 0);
    this.assertEmpty(result.steps);
-    this.assertEqual(result.gdpMultiplier, 1);
+    this.assertEqual(result.productionMultiplier, 1);
  }

  test_effect_value_is_zero_for_a_non_positive_level() {
@@ -0,0 +1,681 @@
+import { TestCase } from "./framework/test_case.js";
+import { smallState, cityOf, grantBuilding } from "./framework/helpers.js";
+import { key } from "../shared/hex.js";
+import {
+  RESOURCE_RULES,
+  RESOURCE_MARKET_BASE,
+  RESOURCE_BUILDINGS,
+  EFFECT_RESEARCH,
+  technologyCost,
+} from "../shared/data.js";
+import { DAYS_PER_YEAR } from "../shared/game_state/constants.js";
+import {
+  formatEnergy,
+  formatResourceAmount,
+  foodNeedPerDay,
+  steelNeedPerDay,
+  luxuryNeedPerDay,
+  foodMonthlyTarget,
+  cityEnergyPerDay,
+  deliveryEnergyKwh,
+  deliveryEnergyForResource,
+  nextMarketPrice,
+} from "../shared/resources.js";
+
+function freeLandTile(state, civ = 0) {
+  for (const coords of state._territoryByCiv.get(civ) || []) {
+    if (state.cityAt(coords)) continue;
+    if (state.tileImprovements.has(key(coords.x, coords.y))) continue;
+    if (state._isLand(coords)) return coords;
+  }
+  return null;
+}
+
+function placeResourceBuilding(state, coords, id, civ = 0) {
+  const k = key(coords.x, coords.y);
+  state.tileImprovements.set(k, id);
+  state.tileImprovementOwner.set(k, civ);
+  state.tileImprovementHp.set(k, 1000);
+  state._ensureResourceStock(k);
+  return k;
+}
+
+export class ResourceRulesTest extends TestCase {
+  test_energy_formats_in_friendly_units() {
+    this.assertEqual(formatEnergy(500), "500 kWh");
+    this.assertTrue(formatEnergy(1_500).includes("MWh"));
+    this.assertTrue(formatEnergy(2_500_000).includes("GWh"));
+    this.assertTrue(formatEnergy(3_000_000_000).includes("TWh"));
+  }
+
+  test_material_units_step_up() {
+    this.assertEqual(formatResourceAmount("steel", 250), "250 t");
+    this.assertTrue(formatResourceAmount("steel", 2_500_000).includes("kt"));
+    this.assertTrue(formatResourceAmount("steel", 2_500_000_000).includes("Mt"));
+    this.assertTrue(formatResourceAmount("luxury", 2500).includes("ct"));
+  }
+
+  test_per_person_needs_follow_the_rules() {
+    // 1 kg a day of food and steel, 0.01 ct of luxury, for 2 million people.
+    this.assertApprox(foodNeedPerDay(2_000_000), 2000);
+    this.assertApprox(steelNeedPerDay(2_000_000), 2000);
+    this.assertApprox(luxuryNeedPerDay(2_000_000), 20_000);
+  }
+
+  test_food_target_is_a_month_with_a_cushion() {
+    const need = foodNeedPerDay(2_000_000) * 30 * RESOURCE_RULES.foodMonthlyBuffer;
+    this.assertApprox(foodMonthlyTarget(2_000_000), need);
+  }
+
+  test_city_energy_scales_with_gdp() {
+    this.assertApprox(cityEnergyPerDay(0), 0);
+    this.assertGreater(cityEnergyPerDay(1e11), 0);
+  }
+
+  test_delivery_energy_matches_the_roadmap_figures() {
+    // 1 tonne, 1 tile: 10 MWh by road, 1 MWh by train, 50 kWh by ship.
+    this.assertApprox(deliveryEnergyKwh(1, 1, "road"), 10_000);
+    this.assertApprox(deliveryEnergyKwh(1, 1, "train"), 1_000);
+    this.assertApprox(deliveryEnergyKwh(1, 1, "ship"), 50);
+    // Off-road trucks burn 50 MWh a tile, times the tile's movement cost.
+    this.assertApprox(deliveryEnergyKwh(1, 1, "truck", 4), 200_000);
+  }
+
+  test_energy_delivery_counts_ten_gwh_per_tonne() {
+    // Delivering 10 GWh of energy is one tonne, so its transport is the same
+    // as moving one tonne of steel the same distance.
+    const asEnergy = deliveryEnergyForResource("energy", 10_000_000, 1, "road");
+    const asSteel = deliveryEnergyForResource("steel", 1, 1, "road");
+    this.assertApprox(asEnergy, asSteel);
+  }
+
+  test_market_price_rises_on_shortage_and_falls_on_glut() {
+    const base = RESOURCE_MARKET_BASE.steel;
+    const scarce = nextMarketPrice(base, base, 10, 20);
+    const glut = nextMarketPrice(base, base, 20, 10);
+    this.assertGreater(scarce, base);
+    this.assertLess(glut, base);
+  }
+}
+
+export class ResourceModelTest extends TestCase {
+  test_cities_start_with_a_food_store() {
+    const state = smallState();
+    for (const city of state.cities) {
+      const stock = state.getCityResourceStock(city);
+      this.assertGreater(stock.food, 0, "the city opens with food");
+      this.assertGreater(stock.steel, 0, "the city opens with steel");
+    }
+  }
+
+  test_construction_resource_cost_follows_the_money_cost() {
+    const state = smallState();
+    const cost = state.constructionResourceCost({ buildCost: 1_000_000, effects: [] });
+    this.assertApprox(cost.steel, 1_000_000 * RESOURCE_RULES.steelPerBudgetEuro);
+    this.assertEqual(cost.hightech, 0);
+    const lab = state.protoBuildings.find((b) => b.id === "research_lab");
+    this.assertGreater(state.constructionResourceCost(lab, 0, lab.baseCost).hightech, 0);
+  }
+
+  test_resource_money_tracks_buying_and_selling() {
+    const state = smallState();
+    state._recordResourceSpend(0, "goods", 1000, "steel");
+    state._recordResourceEarn(0, "steel", 400);
+    const breakdown = state.budgetBreakdown(0);
+    const steel = breakdown.resourceMoney.find((entry) => entry.id === "steel");
+    this.assertNotNull(steel, "steel appears in the trade breakdown");
+    this.assertApprox(steel.bought, 1000);
+    this.assertApprox(steel.sold, 400);
+  }
+
+  test_national_gdp_per_capita_matches_the_regions() {
+    const state = smallState();
+    const snapshot = state.snapshot(0);
+    let gdp = 0;
+    let population = 0;
+    for (const city of state.cities) {
+      if (city.civ !== 0) continue;
+      const stats = snapshot.cityStats.find((entry) => entry.id === city.id);
+      gdp += stats.gdp;
+      population += stats.population;
+    }
+    this.assertApprox(snapshot.viewerStats.gdpPerCapita, gdp / population, 1e-6);
+  }
+
+  test_construction_draws_steel_from_the_city_before_the_market() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const stock = state.getCityResourceStock(city);
+    stock.steel = 1000;
+    const before = state.getBudget(0);
+    const ok = state._payConstructionResources(0, city.coords, { steel: 400, hightech: 0 });
+    this.assertTrue(ok);
+    this.assertApprox(stock.steel, 600, 1e-6, "steel came out of the store");
+    this.assertApprox(state.getBudget(0), before, 1e-6, "no market bill was needed");
+  }
+
+  test_construction_buys_the_shortfall_on_the_market() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    // Every city of the nation must be empty, or the draw would find another
+    // store before it reaches the market.
+    for (const own of state.cities) {
+      if (own.civ === 0) state.getCityResourceStock(own).steel = 0;
+    }
+    const price = state.getResourcePrice("steel");
+    const before = state.getBudget(0);
+    const ok = state._payConstructionResources(0, city.coords, { steel: 1000, hightech: 0 });
+    this.assertTrue(ok);
+    this.assertApprox(before - state.getBudget(0), 1000 * price, 1e-3);
+  }
+
+  test_research_spends_high_tech() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    grantBuilding(state, city, "research_lab");
+    const tech = state.technologies.findIndex((t) => t.id === "scientific_method");
+    this.assertTrue(state.requestFocusTechnology(0, tech));
+    const governmentRate = state.getCivGovernmentModifiers(0)[EFFECT_RESEARCH] || 0;
+    // With a store of high-tech the lab's one point an hour comes through.
+    for (const own of state.cities) {
+      if (own.civ === 0) state.getCityResourceStock(own).hightech = 1000;
+    }
+    const before = state.getTechnologyProgress(0, tech);
+    state.advanceHour();
+    const withTech = state.getTechnologyProgress(0, tech) - before;
+    this.assertApprox(withTech, governmentRate + 1.0, 1e-6);
+    // With no store, the lab's point is simply not produced.
+    for (const own of state.cities) {
+      if (own.civ === 0) state.getCityResourceStock(own).hightech = 0;
+    }
+    const before2 = state.getTechnologyProgress(0, tech);
+    state.advanceHour();
+    const withoutTech = state.getTechnologyProgress(0, tech) - before2;
+    this.assertApprox(withoutTech, governmentRate, 1e-6);
+  }
+
+  test_a_power_plant_supplies_its_grid() {
+    const withPlant = smallState();
+    const tile = freeLandTile(withPlant, 0);
+    placeResourceBuilding(withPlant, tile, "coal_power_plant", 0);
+    withPlant._tickResources();
+    const stats = withPlant.resourceMarketStats.get("energy");
+    this.assertGreater(stats.supply, 0, "the plant fed the grid");
+  }
+
+  test_gdp_is_the_market_value_of_what_a_region_produces() {
+    const state = smallState();
+    const tile = freeLandTile(state, 0);
+    const region = state.regionCityAt(tile);
+    this.assertNotNull(region, "the tile belongs to a region");
+    const before = state._regionProductionValue(region);
+    placeResourceBuilding(state, tile, "steel_mill", 0);
+    const after = state._regionProductionValue(region);
+    const proto = RESOURCE_BUILDINGS.find((b) => b.id === "steel_mill");
+    const outputValue = proto.outputPerDay * state.getResourcePrice("steel") * DAYS_PER_YEAR;
+    this.assertApprox(after - before, outputValue, outputValue * 1e-6, "the mill's output is GDP");
+  }
+
+  test_a_steel_mill_consumes_energy_and_makes_steel() {
+    const state = smallState();
+    const plantTile = freeLandTile(state, 0);
+    placeResourceBuilding(state, plantTile, "coal_power_plant", 0);
+    // A second owned tile for the mill, away from the city.
+    const millTile = state._territoryByCiv.get(0).find(
+      (coords) => state._isLand(coords) && !state.cityAt(coords) &&
+        key(coords.x, coords.y) !== key(plantTile.x, plantTile.y)
+    );
+    const k = placeResourceBuilding(state, millTile, "steel_mill", 0);
+    state._tickResources();
+    const stock = state._ensureResourceStock(k);
+    this.assertGreater(stock.steel, 0, "the mill produced steel");
+  }
+
+  test_a_city_buys_from_a_neighbour_before_the_market() {
+    const state = smallState();
+    const cities = state.cities.filter((c) => c.civ === 0);
+    this.assertGreaterOrEqual(cities.length, 2, "the fixture has two cities");
+    const buyer = cities[0];
+    const seller = cities[1];
+    state.getCityResourceStock(seller).food = 1e9;
+    state.getCityResourceStock(buyer).food = 0;
+    const store = state.getCityResourceStock(buyer);
+    const bought = state._procureFromNeighbours(
+      buyer, "food", 1000, store, state._resourceNodes()
+    );
+    this.assertGreater(bought, 0, "the neighbour sold food");
+    this.assertGreater(store.food, 0, "the buyer received it");
+    this.assertTrue(
+      state.resourceLinks.some((link) => link.resource === "food"),
+      "the delivery is on the graph"
+    );
+  }
+
+  test_foreign_trade_runs_on_the_transport_network() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const buyer = cityOf(state, 0);
+    const seller = cityOf(state, 1);
+    state.getCityResourceStock(seller).food = 1e9;
+    state.getCityResourceStock(buyer).food = 0;
+    const store = state.getCityResourceStock(buyer);
+    const boughtOnNetwork = state._procureFromNeighbours(
+      buyer, "food", 1000, store, state._resourceNodes()
+    );
+    this.assertGreater(boughtOnNetwork, 0, "a foreign market on the network is reachable");
+
+    // Tear up every road and railway: the foreign market is now unreachable.
+    state.roads.clear();
+    state.railways.clear();
+    store.food = 0;
+    state.resourceLinks = [];
+    const boughtOffNetwork = state._procureFromNeighbours(
+      buyer, "food", 1000, store, state._resourceNodes()
+    );
+    this.assertEqual(boughtOffNetwork, 0, "no road, no foreign market");
+  }
+
+  test_cross_nation_deliveries_are_booked_as_imports_and_exports() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const buyer = cityOf(state, 0);
+    const seller = cityOf(state, 1);
+    state.getCityResourceStock(seller).food = 1e9;
+    state.getCityResourceStock(buyer).food = 0;
+    const bought = state._procureFromNeighbours(
+      buyer, "food", 1000, state.getCityResourceStock(buyer), state._resourceNodes()
+    );
+    this.assertGreater(bought, 0, "the neighbour sold food");
+    this.assertApprox(state._civResourceTrade(0).imports.food, bought, 1e-6, "the buyer imported it");
+    this.assertApprox(state._civResourceTrade(1).exports.food, bought, 1e-6, "the seller exported it");
+    // The snapshot carries every nation's trade ledger, so the panel can rank
+    // the world's major exporters and importers.
+    const snapshot = state.snapshot(0);
+    this.assertSize(snapshot.resourceTrade, 2);
+    this.assertApprox(snapshot.resourceTrade[1].exports.food, bought, 1e-3);
+  }
+
+  test_a_shortage_costs_popularity() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const before = state.getCivPopularity(0);
+    state._resourceShortages.set(city.id, { steel: 1 });
+    state._applyResourceShortages(new Map());
+    this.assertLess(state.getCivPopularity(0), before, "a shortage hurt the government");
+  }
+
+  test_a_resource_building_cannot_stand_inside_a_city() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    this.assertFalse(
+      state.requestBuildTileImprovement(0, city.coords, "coal_power_plant"),
+      "a power plant belongs on open land"
+    );
+    const tile = freeLandTile(state, 0);
+    state.budgets.set(0, 1e15);
+    this.assertTrue(
+      state.requestBuildTileImprovement(0, tile, "coal_power_plant"),
+      "and is accepted on a controlled land tile"
+    );
+  }
+
+  test_snapshot_ships_the_market_and_the_delivery_graph() {
+    const state = smallState();
+    const snapshot = state.snapshot(0);
+    this.assertSize(snapshot.resourceMarket, 5);
+    for (const entry of snapshot.resourceMarket) {
+      this.assertHas(entry, "price");
+      this.assertGreater(entry.price, 0);
+    }
+    this.assertHas(snapshot.viewerStats, "resources");
+    this.assertHas(snapshot.resourceGraph, "nodes");
+    this.assertHas(snapshot.resourceGraph, "links");
+  }
+
+  // ------------------------------------------------- starting industry ----
+
+  test_the_opening_economy_is_seeded_with_covering_industry() {
+    const state = smallState();
+    this.assertGreater(state.tileImprovements.size, 0, "the world opens with resource works");
+    const components = state._resourceLandComponents();
+    const foodEnergy = state._foodEnergyByComponent(components);
+    for (let civ = 0; civ < state.civilisations.length; civ++) {
+      const deficits = state._resourceSeedDeficits(civ);
+      this.assertTrue(deficits.steel <= 0, "steel production covers the people and the works");
+      this.assertTrue(deficits.luxury <= 0, "luxury production covers the people");
+      const energy = state._resourceSeedEnergy(civ, components, foodEnergy);
+      this.assertEmpty(energy, "every grid has the power its cities and industry draw");
+    }
+  }
+
+  test_seeded_industry_is_connected_to_the_transport_network() {
+    const state = smallState();
+    this.assertGreater(state.tileImprovements.size, 0, "there are seeded works");
+    for (const k of state.tileImprovements.keys()) {
+      this.assertTrue(
+        state.roads.has(k) || state.railways.has(k),
+        "a seeded work sits on the transport network"
+      );
+    }
+  }
+
+  test_seeding_is_deterministic_from_the_world_seed() {
+    const first = smallState(["france", "britain"], 12345);
+    const again = smallState(["france", "britain"], 12345);
+    const other = smallState(["france", "britain"], 999);
+    const describe = (state) =>
+      Array.from(state.tileImprovements.entries())
+        .map(([k, id]) => `${k}:${id}`)
+        .sort()
+        .join("|");
+    this.assertEqual(describe(first), describe(again), "the same seed lays out the same works");
+    this.assertNotEqual(describe(first), describe(other), "a different seed lays out different works");
+  }
+
+  // ------------------------------------------------------- upkeep -------
+
+  test_building_upkeep_is_materials_per_level_per_day() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    const before = state.getBuildingUpkeep(0);
+    const index = grantBuilding(state, city, "research_lab", 1);
+    const after = state.getBuildingUpkeep(0);
+    // A 100 M lab: 50 t of steel, 100 MWh of energy and 200 high-tech a day.
+    this.assertApprox(after.steel - before.steel, 50, 1e-6);
+    this.assertApprox(after.hightech - before.hightech, 200, 1e-6);
+    const beforeLevel = after.steel;
+    city.buildings[index] = 2;
+    this.assertGreater(state.getBuildingUpkeep(0).steel, beforeLevel, "a higher level wears more");
+  }
+
+  test_the_state_pays_upkeep_materials_from_the_budget() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    grantBuilding(state, city, "market", 4);
+    // Drain the stores so the day's upkeep has to be bought.
+    for (const own of state.cities) {
+      if (own.civ === 0) state.getCityResourceStock(own).steel = 0;
+    }
+    state.advanceHour();
+    // The material bill is settled on the daily tick, not hourly.
+    for (let i = 0; i < 23; i++) state.advanceHour();
+    const spend = state.resourceSpend.get(0) || {};
+    this.assertGreater(spend.upkeep || 0, 0, "the spend is booked as upkeep");
+    // The materials bill lands in the month's budget under an upkeep category.
+    const report = state.budgetMonthReports(0).at(-1);
+    const upkeep = report.expenses.filter(
+      (entry) => ["buildings", "units", "works", "transport"].includes(entry.id)
+    );
+    this.assertGreater(upkeep.length, 0, "the treasury paid it, filed as upkeep");
+  }
+
+  test_unaffordable_upkeep_costs_popularity() {
+    const state = smallState();
+    const before = state.getCivPopularity(0);
+    state._civilianUpkeepShortage(0, 1);
+    this.assertLess(state.getCivPopularity(0), before, "an unpaid bill is unrest");
+  }
+
+  // ------------------------------------------------------- repairs ------
+
+  test_a_razed_building_level_is_rebuilt_with_materials() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    const index = grantBuilding(state, city, "market", 1);
+    city.buildings[index] = 0;
+    state._queueCityRepair(city, index, 1);
+    state._tickRepairs();
+    this.assertEqual(city.buildings[index], 1, "the level came back once its materials were paid");
+  }
+
+  test_a_damaged_tile_work_heals_once_its_debt_is_paid() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const tile = freeLandTile(state, 0);
+    const k = placeResourceBuilding(state, tile, "fortifications", 0);
+    state.tileImprovementHp.set(k, 200);
+    state._recordRepairDebt(tile, 200);
+    const debt = state.tileRepairDebt.get(k);
+    this.assertGreater(debt, 0, "damage left a debt");
+    for (let i = 0; i < 20; i++) state._tickRepairs();
+    this.assertFalse(state.tileRepairDebt.has(k), "the debt was paid off");
+    this.assertGreater(state.tileImprovementHp.get(k), 200, "the work healed");
+  }
+
+  test_a_damaged_unit_heals_at_a_materials_cost() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    const unit = state._spawnUnit(city.coords, 0, state.protoUnits[0]);
+    unit.hp = 100;
+    // Empty the stores so the heal must be bought.
+    for (const own of state.cities) {
+      if (own.civ === 0) state.getCityResourceStock(own).steel = 0;
+    }
+    const before = state.getBudget(0);
+    state._tickGarrisonHealing();
+    this.assertGreater(unit.hp, 100, "the unit healed");
+    this.assertLess(state.getBudget(0), before, "healing cost the treasury");
+  }
+
+  test_a_tile_with_repair_debt_does_not_recover_its_gdp() {
+    const state = smallState();
+    const tile = freeLandTile(state, 0);
+    const k = key(tile.x, tile.y);
+    state.tileBattleProductionDeficit.set(k, 1000);
+    state.tileBattleRecoveryStart.set(k, 0);
+    state._recordRepairDebt(tile, 100);
+    state._tickProductionRecovery();
+    this.assertApprox(state.tileBattleProductionDeficit.get(k), 1000, 1e-6, "the scar waits for its materials");
+  }
+
+  // ------------------------------------------------ tech gate / combat --
+
+  test_fusion_needs_its_technology() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const tile = freeLandTile(state, 0);
+    this.assertFalse(
+      state.requestBuildTileImprovement(0, tile, "fusion_power_plant"),
+      "fusion is locked without the technology"
+    );
+    const index = state.technologies.findIndex((t) => t.id === "fusion_power");
+    this.assertGreater(index, 0, "the fusion technology exists");
+    this.assertEqual(technologyCost(state.technologies[index]), 500_000, "it costs half a million points");
+    state.researched.get(0).add(index);
+    state.budgets.set(0, 1e15);
+    this.assertTrue(
+      state.requestBuildTileImprovement(0, tile, "fusion_power_plant"),
+      "and unlocks the plant once researched"
+    );
+  }
+
+  test_infantry_food_multiplies_in_combat_and_when_resting() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const proto = state.protoUnits.find((p) => p.id === "modern_infantry");
+    const unit = state._spawnUnit(city.coords, 0, proto);
+    const base = foodNeedPerDay(proto.population);
+    this.assertApprox(state._unitFoodRate(unit, proto, false), base, 1e-9, "idle rations");
+    this.assertApprox(
+      state._unitFoodRate(unit, proto, true),
+      base * RESOURCE_RULES.infantryCombatFoodMultiplier,
+      1e-9,
+      "combat rations"
+    );
+    unit.hp = 100;
+    this.assertApprox(
+      state._unitFoodRate(unit, proto, false),
+      base * RESOURCE_RULES.infantryRestingFoodMultiplier,
+      1e-9,
+      "wounded and resting rations"
+    );
+  }
+
+  test_a_land_unit_carries_fifty_days_of_food() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const proto = state.protoUnits.find((p) => p.id === "modern_infantry");
+    const unit = state._spawnUnit(city.coords, 0, proto);
+    this.assertEqual(unit.foodDays, RESOURCE_RULES.unitSupplyDays, "a full pack");
+  }
+
+  test_a_supplied_land_unit_tops_up_its_pack() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const proto = state.protoUnits.find((p) => p.id === "modern_infantry");
+    const unit = state._spawnUnit(city.coords, 0, proto);
+    unit.foodDays = 10;
+    state._tickUnitSupply();
+    this.assertEqual(unit.foodDays, RESOURCE_RULES.unitSupplyDays, "it is fed at home");
+  }
+
+  test_a_cut_off_land_unit_starves() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const proto = state.protoUnits.find((p) => p.id === "modern_infantry");
+    const unit = state._spawnUnit(city.coords, 0, proto);
+    // No reachable allied city, and an empty pack: the soldiers start dying.
+    state._unitSupplyCity = () => null;
+    unit.foodDays = 0;
+    const before = unit.hp;
+    state._tickUnitSupply();
+    this.assertLess(unit.hp, before, "starvation costs hit points");
+  }
+
+  test_air_and_naval_units_do_not_carry_supply() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const jet = state.protoUnits.find((p) => p.id === "jet_fighter");
+    const unit = state._spawnUnit(city.coords, 0, jet, city.id);
+    unit.foodDays = 5;
+    state._unitSupplyCity = () => null;
+    state._tickUnitSupply();
+    this.assertEqual(unit.foodDays, 5, "an aircraft uses endurance, not a food pack");
+  }
+
+  test_an_encircled_city_cannot_buy_from_the_market() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    // Ring the city with enemies and empty its stores.
+    for (const neighbour of state.topology.neighbours(city.coords.x, city.coords.y)) {
+      if (state._isLand(neighbour)) state._spawnUnit(neighbour, 1, state.protoUnits[0]);
+    }
+    const store = state.getCityResourceStock(city);
+    store.food = 0;
+    store.steel = 0;
+    store.luxury = 0;
+    const market = new Map(
+      ["food", "steel", "luxury", "energy", "hightech"].map((id) => [id, { demand: 0 }])
+    );
+    state._consumeCityResources(new Map(), market);
+    this.assertEqual(store.food, 0, "no food came in through the ring");
+    this.assertGreater(state._resourceShortages.size, 0, "the shortage is recorded");
+  }
+
+  test_an_encircled_unit_cannot_resupply() {
+    const state = smallState();
+    const unit = state.units[0];
+    for (const neighbour of state.topology.neighbours(unit.coords.x, unit.coords.y)) {
+      if (state._isLand(neighbour)) state._spawnUnit(neighbour, 1, state.protoUnits[0]);
+    }
+    unit.foodDays = 10;
+    state._tickUnitSupply();
+    this.assertLess(unit.foodDays, 10, "a cut-off unit eats its reserves");
+  }
+
+  test_a_unit_off_the_network_starves() {
+    const state = smallState();
+    const proto = state.protoUnits.find((p) => p.id === "modern_infantry");
+    const tile = freeLandTile(state, 0);
+    const unit = state._spawnUnit(tile, 0, proto);
+    // Tear up the network: the unit is cut off and eats its reserves.
+    state.roads.clear();
+    state.railways.clear();
+    unit.foodDays = 10;
+    state._tickUnitSupply();
+    this.assertLess(unit.foodDays, 10, "no road, no resupply");
+  }
+
+  test_naval_cities_start_with_a_port() {
+    const state = smallState();
+    const coastal = state.cities.find((c) => c.civ === 0 && state.isCoastalCity(c));
+    const inland = state.cities.find((c) => c.civ === 0 && !state.isCoastalCity(c));
+    this.assertNotNull(coastal, "the nation has a naval city");
+    this.assertTrue(state.hasCityBuilding(coastal, "port"), "a naval city starts with a port");
+    this.assertFalse(inland && state.hasCityBuilding(inland, "port"), "an inland city does not");
+  }
+
+  test_a_city_without_a_port_has_no_foreign_market() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    const store = state.getCityResourceStock(city);
+    const portIndex = state.protoBuildings.findIndex((b) => b.id === "port");
+    for (const own of state.cities) {
+      if (own.civ === 0) delete own.buildings[portIndex];
+    }
+    this.assertFalse(state._civMarketAccess(0), "no working port, no market");
+    this.assertEqual(state._buyMarketMaterial(city, "food", 100, store), 0, "nothing can be bought");
+
+    const coastal = state.cities.find((c) => c.civ === 0 && state.isCoastalCity(c));
+    coastal.buildings[portIndex] = 1;
+    this.assertTrue(state._civMarketAccess(0), "the port opens the market");
+    this.assertGreater(state._buyMarketMaterial(city, "food", 100, store), 0, "goods now arrive");
+  }
+
+  test_air_defense_spends_ammunition_when_it_fires() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    grantBuilding(state, city, "aa_building");
+    for (const own of state.cities) {
+      if (own.civ === 0) {
+        const store = state.getCityResourceStock(own);
+        store.steel = 0;
+        store.hightech = 0;
+      }
+    }
+    const plane = state.protoUnits.find((p) => p.id === "jet_fighter");
+    const intruder = state._spawnUnit(city.coords, 1, plane);
+    state._airDefenseVolley(intruder);
+    const spend = state.resourceSpend.get(0) || {};
+    this.assertGreater(spend.combat || 0, 0, "firing the air defense cost materials");
+  }
+
+  test_training_a_unit_draws_its_soldiers_from_the_region() {
+    const state = smallState();
+    const city = cityOf(state, 0);
+    const proto = state.protoUnits.find((p) => p.id === "modern_infantry");
+    const before = state.regionPopulation(city);
+    state._spawnTrainedUnit(city, proto);
+    const after = state.regionPopulation(city);
+    this.assertApprox(before - after, proto.population, 1e-6, "1000 people became soldiers");
+  }
+
+  test_healing_a_unit_draws_replacement_soldiers() {
+    const state = smallState();
+    state.budgets.set(0, 1e15);
+    const city = cityOf(state, 0);
+    const proto = state.protoUnits.find((p) => p.id === "modern_infantry");
+    const unit = state._spawnUnit(city.coords, 0, proto);
+    unit.hp = 100;
+    const before = state.regionPopulation(city);
+    state._tickGarrisonHealing();
+    const gained = unit.hp - 100;
+    this.assertGreater(gained, 0, "the unit healed");
+    // Each hit point is a share of the unit's soldiers, drawn from the people.
+    this.assertApprox(
+      before - state.regionPopulation(city),
+      (gained / unit.maxHp) * proto.population,
+      1e-6
+    );
+  }
+}
@@ -11,15 +11,15 @@ import {
  defenseFactors,
  defenseMultiplier,
  unitDefense,
-  gdpPerCapitaFactors,
-  gdpPerCapitaFromFactors,
+  productionFactors,
+  productionFromFactors,
 } from "../shared/rules.js";
 import {
  effectValue,
  GOVERNMENTS,
  TECHNOLOGIES,
  TERRAIN_TILES,
-  EFFECT_GDP,
+  EFFECT_PRODUCTION,
  EFFECT_RESEARCH,
  EFFECT_CULTURE,
 } from "../shared/data.js";
@@ -75,15 +75,15 @@ export class RulesTest extends TestCase {
  test_building_effect_value_sums_matching_stats() {
    const building = proto({
      effects: [
-        { stat: "gdp", baseValue: 0.04, exponent: 0.75 },
-        { stat: "gdp", baseValue: 0.01, exponent: 1.0 },
+        { stat: "production", baseValue: 0.04, exponent: 0.75 },
+        { stat: "production", baseValue: 0.01, exponent: 1.0 },
        { stat: "culture", baseValue: 1.0, exponent: 1.0 },
      ],
    });
-    this.assertApprox(buildingEffectValue(building, "gdp", 1), 0.05);
+    this.assertApprox(buildingEffectValue(building, "production", 1), 0.05);
    this.assertApprox(buildingEffectValue(building, "culture", 1), 1.0);
    this.assertEqual(buildingEffectValue(building, "research", 1), 0);
-    this.assertEqual(buildingEffectValue(building, "gdp", 0), 0);
+    this.assertEqual(buildingEffectValue(building, "production", 0), 0);
  }

  test_government_change_cost() {
@@ -95,7 +95,7 @@ export class RulesTest extends TestCase {

  test_catalogue_effects() {
    const monarchy = GOVERNMENTS.find((g) => g.id === "monarchy");
-    this.assertApprox(governmentEffects(monarchy)[EFFECT_GDP], 0.1);
+    this.assertApprox(governmentEffects(monarchy)[EFFECT_PRODUCTION], 0.1);
    this.assertApprox(governmentEffects(monarchy)[EFFECT_CULTURE], 1.0);
    const technocracy = GOVERNMENTS.find((g) => g.id === "technocracy");
    this.assertGreater(
@@ -104,7 +104,7 @@ export class RulesTest extends TestCase {
    );
    const method = TECHNOLOGIES.find((t) => t.id === "scientific_method");
    this.assertApprox(technologyEffects(method)[EFFECT_RESEARCH], 1.0);
-    this.assertApprox(technologyEffects(method)[EFFECT_GDP], 0.02);
+    this.assertApprox(technologyEffects(method)[EFFECT_PRODUCTION], 0.02);
  }

  test_prerequisites_met() {
@@ -174,40 +174,40 @@ export class RulesTest extends TestCase {
    this.assertApprox(bonusOf("Land"), 0);
  }

-  test_gdp_per_capita_factors_name_the_terrain_and_settlement() {
+  test_production_factors_name_the_terrain_and_settlement() {
    const plains = TERRAIN_TILES.find((t) => t.terrainType === "Land");
-    const base = gdpPerCapitaFactors(plains);
+    const base = productionFactors(plains);
    this.assertSize(base, 1);
    this.assertEqual(base[0].label, "Land");
    this.assertApprox(base[0].multiplier, 1);

-    const city = gdpPerCapitaFactors(plains, { cityKind: "city" });
+    const city = productionFactors(plains, { cityKind: "city" });
    this.assertSize(city, 2);
    this.assertEqual(city[1].label, "City");
    this.assertApprox(city[1].multiplier, 2);

-    const capital = gdpPerCapitaFactors(plains, { cityKind: "capital" });
+    const capital = productionFactors(plains, { cityKind: "capital" });
    this.assertApprox(capital[1].multiplier, 2.5);

-    const near = gdpPerCapitaFactors(plains, { nextToCity: true });
+    const near = productionFactors(plains, { nextToCity: true });
    this.assertEqual(near[1].label, "Near city");
    this.assertApprox(near[1].multiplier, 1.3);
  }

-  test_gdp_per_capita_factors_include_the_marks_of_war() {
+  test_production_factors_include_the_marks_of_war() {
    const plains = TERRAIN_TILES.find((t) => t.terrainType === "Land");
-    const factors = gdpPerCapitaFactors(plains, { pillagePenalty: 0.7, battleDeficit: 500 });
+    const factors = productionFactors(plains, { pillagePenalty: 0.7, battleDeficit: 500 });
    this.assertEqual(factors[1].label, "Pillaging");
    this.assertApprox(factors[1].multiplier, 0.7);
    this.assertEqual(factors[2].label, "Battle damage");
    this.assertApprox(factors[2].amount, -500);
  }

-  test_gdp_per_capita_from_factors_applies_in_order_and_floors_at_zero() {
+  test_production_from_factors_applies_in_order_and_floors_at_zero() {
    this.assertApprox(
-      gdpPerCapitaFromFactors(10000, [{ multiplier: 2 }, { amount: -500 }]),
+      productionFromFactors(10000, [{ multiplier: 2 }, { amount: -500 }]),
      19500
    );
-    this.assertEqual(gdpPerCapitaFromFactors(100, [{ amount: -500 }]), 0);
+    this.assertEqual(productionFromFactors(100, [{ amount: -500 }]), 0);
  }
 }
@@ -1,7 +1,7 @@
 import { TestCase } from "./framework/test_case.js";
 import { setupDom, teardownDom } from "./framework/dom.js";
-import { smallState, mapLayers, SEED } from "./framework/helpers.js";
-import { parseKey } from "../shared/hex.js";
+import { smallState, mapLayers, SEED, grantBuilding } from "./framework/helpers.js";
+import { parseKey, key } from "../shared/hex.js";
 import { CIVILISATIONS, PROTO_UNITS, statusById, STATUS_ENCIRCLED, STATUS_BESIEGED } from "../shared/data.js";
 import { MapView } from "../client/js/map_view.js";

@@ -28,44 +28,18 @@ export class SiegeTest extends TestCase {
    }
  }

-  // The supply check only runs when a hostile is adjacent: the daily refresh
-  // never calls into the search otherwise.
-  test_the_check_only_triggers_with_an_adjacent_hostile() {
-    const state = smallState();
-    const unit = state.units[0];
-    const neighbours = state.topology.neighbours(unit.coords.x, unit.coords.y).filter(
-      (n) => state._isLand(n) && !state.unitAt(n) && !state.cityAt(n)
-    );
-    this.assertGreaterOrEqual(neighbours.length, 2, "the capital has open land around it");
-
-    let calls = 0;
-    const original = state._unitStatuses.bind(state);
-    state._unitStatuses = (...args) => {
-      calls += 1;
-      return original(...args);
-    };
-
-    state._refreshStatuses();
-    this.assertEqual(calls, 0, "no hostile, no supply search");
-
-    state._spawnUnit(neighbours[0], 0, state.protoUnits[0]);
-    state._refreshStatuses();
-    this.assertEqual(calls, 0, "a friendly neighbour does not trigger it");
-
-    state._spawnUnit(neighbours[1], 1, state.protoUnits[0]);
-    state._refreshStatuses();
-    this.assertGreater(calls, 0, "a hostile neighbour triggers the check");
-    this.assertEmpty(unit.statuses, "the unit is still supplied");
-  }
-
-  test_a_cut_off_unit_with_a_hostile_neighbour_is_encircled() {
+  test_a_gap_in_the_ring_frees_the_unit() {
    const state = smallState();
    const tile = findSurroundableTile(state);
-    this.assertNotNull(tile, "found an interior tile to surround");
    const unit = state._spawnUnit(tile, 0, state.protoUnits[0]);
-    surroundTile(state, tile, 1);
+    const blockers = surroundTile(state, tile, 1);
    state._refreshStatuses();
-    this.assertEqual(unit.statuses, [STATUS_ENCIRCLED]);
+    this.assertEqual(unit.statuses, [STATUS_ENCIRCLED], "a full ring encircles");
+
+    // Opening one land tile -- an allied unit or an empty tile -- breaks it.
+    state._destroyUnit(blockers[0]);
+    state._refreshStatuses();
+    this.assertEmpty(unit.statuses, "one open land tile frees the unit");
  }

  test_a_friendly_neighbour_does_not_trigger_encirclement() {
@@ -106,13 +80,13 @@ export class SiegeTest extends TestCase {
    this.assertApprox(unit.hp, before - unit.maxHp * 0.02);
  }

-  test_a_lone_city_can_never_be_besieged() {
+  test_a_lone_city_can_be_besieged() {
    const state = smallState(["france"], SEED, { citiesPerCiv: 1 });
    const city = state.cities[0];
    this.assertNotNull(city);
    surroundTile(state, city.coords, 1);
    state._refreshStatuses();
-    this.assertEmpty(city.statuses, "a city with no sibling is not besieged");
+    this.assertEqual(city.statuses, [STATUS_BESIEGED], "a surrounded portless city is besieged");
  }

  test_status_is_refreshed_once_a_day_not_every_snapshot() {
@@ -136,35 +110,32 @@ export class SiegeTest extends TestCase {
    this.assertEmpty(unit.statuses, "the daily refresh freed the unit");
  }

-  test_an_allied_naval_unit_lifts_a_siege_across_water() {
+  test_a_port_survives_a_land_ring_and_falls_to_a_blockade() {
    const state = smallState();
-    const spot = findCoastalPair(state);
-    this.assertNotNull(spot, "found a sea tile between two land tiles");
-    const unit = state._spawnUnit(spot.l1, 0, state.protoUnits[0]);
-    surroundTile(state, spot.l1, 1);
+    const city = findCoastalClearCity(state, 0);
+    this.assertNotNull(city, "found a coastal city with a clear land ring");
+    grantBuilding(state, city, "port");
+    surroundTile(state, city.coords, 1);
    state._refreshStatuses();
-    this.assertEqual(unit.statuses, [STATUS_ENCIRCLED], "cut off by land");
+    this.assertEmpty(city.statuses, "the port supplies the city by sea");

-    state._spawnCity({ civIndex: 0, coords: { x: spot.l2.x, y: spot.l2.y }, isCapital: false });
-    state._rebuildCityIndex();
+    // Enemy warships now hold every sea tile around the city.
+    for (const neighbour of state.topology.neighbours(city.coords.x, city.coords.y)) {
+      const tile = state.tiles[key(neighbour.x, neighbour.y)];
+      if (tile && tile.terrainClass === "Sea") state._spawnUnit(neighbour, 1, navalProto());
+    }
    state._refreshStatuses();
-    this.assertEqual(unit.statuses, [STATUS_ENCIRCLED], "no lane without a ship");
-
-    state._spawnUnit({ x: spot.s.x, y: spot.s.y }, 0, navalProto());
-    state._refreshStatuses();
-    this.assertEmpty(unit.statuses, "the friendly navy reopens the lane");
+    this.assertEqual(city.statuses, [STATUS_BESIEGED], "the blockade cuts the sea lane");
  }

-  test_an_enemy_naval_unit_does_not_open_a_lane() {
+  test_an_allied_naval_unit_does_not_break_a_land_ring() {
    const state = smallState();
-    const spot = findCoastalPair(state);
-    const unit = state._spawnUnit(spot.l1, 0, state.protoUnits[0]);
-    surroundTile(state, spot.l1, 1);
-    state._spawnCity({ civIndex: 0, coords: { x: spot.l2.x, y: spot.l2.y }, isCapital: false });
-    state._rebuildCityIndex();
-    state._spawnUnit({ x: spot.s.x, y: spot.s.y }, 1, navalProto());
+    const tile = findSurroundableTile(state);
+    const unit = state._spawnUnit(tile, 0, state.protoUnits[0]);
+    surroundTile(state, tile, 1);
+    state._spawnUnit(tile, 0, navalProto()); // a friendly hull on the same land tile
    state._refreshStatuses();
-    this.assertEqual(unit.statuses, [STATUS_ENCIRCLED], "an enemy fleet is no supply line");
+    this.assertEqual(unit.statuses, [STATUS_ENCIRCLED], "only a port breaks the ring");
  }

  async test_the_client_draws_status_icons_over_units_and_cities() {
@@ -238,7 +209,22 @@ function surroundTile(state, coords, civ) {
 function findBesiegableCity(state, civ) {
  for (const city of state.cities) {
    if (city.civ !== civ) continue;
-    if (state.unitAt(city.coords)) continue;
+    // A coastal city now starts with a port, which keeps it supplied; besiege
+    // an inland city instead.
+    if (state.isCoastalCity(city)) continue;
+    const land = state.topology.neighbours(city.coords.x, city.coords.y).filter((n) => state._isLand(n));
+    if (land.length === 0) continue;
+    if (land.some((n) => state.unitAt(n) || state.cityAt(n))) continue;
+    return city;
+  }
+  return null;
+}
+
+// A coastal city whose land ring is clear, so a port's sea lane can be tested.
+function findCoastalClearCity(state, civ) {
+  for (const city of state.cities) {
+    if (city.civ !== civ) continue;
+    if (!state.isCoastalCity(city)) continue;
    const land = state.topology.neighbours(city.coords.x, city.coords.y).filter((n) => state._isLand(n));
    if (land.length === 0) continue;
    if (land.some((n) => state.unitAt(n) || state.cityAt(n))) continue;
@@ -135,7 +135,7 @@ export class PillageTest extends TestCase {
    this.assertTrue(state.requestPillage([unit.id]));

    this.assertApprox(state.tilePopulation.get(k), 90000, 1);
-    this.assertApprox(state.tileGdpPenalty.get(k), 0.7, 1e-9);
+    this.assertApprox(state.tileProductionPenalty.get(k), 0.7, 1e-9);
    this.assertApprox(state.getTileGdpPerCapita(coords), gdpBefore * 0.7, 1e-6);
    this.assertApprox(unit.hp, 110, 1e-9, "heals 1 HP per 1000 people removed");
  }
@@ -153,7 +153,7 @@ export class PillageTest extends TestCase {
    this.assertTrue(state.requestPillage([strong.id, weak.id]));

    this.assertApprox(state.tilePopulation.get(k), 81000, 1, "90% of 90% remains");
-    this.assertApprox(state.tileGdpPenalty.get(k), 0.49, 1e-9, "70% of 70% remains");
+    this.assertApprox(state.tileProductionPenalty.get(k), 0.49, 1e-9, "70% of 70% remains");
    this.assertApprox(weak.hp, strong.maxHp / 2 + 10, 1e-9, "the weakest pillages first");
    this.assertApprox(strong.hp, strong.maxHp - 100 + 9, 1e-9, "the second heals for the 9000 it removed");
  }
@@ -5,17 +5,17 @@ import { TERRAIN_TILES } from "../shared/data.js";
 export class TerrainStatsTest extends TestCase {
  test_authored_values_are_read() {
    const stats = new TerrainStats({
-      "0,0": { populationMultiplier: 0.3, gdpMultiplier: 0.5, movementCostMultiplier: 1.5 },
+      "0,0": { populationMultiplier: 0.3, productionMultiplier: 0.5, movementCostMultiplier: 1.5 },
    });
    this.assertApprox(stats.populationMultiplier({ x: 0, y: 0 }), 0.3);
-    this.assertApprox(stats.gdpMultiplier({ x: 0, y: 0 }), 0.5);
+    this.assertApprox(stats.productionMultiplier({ x: 0, y: 0 }), 0.5);
    this.assertApprox(stats.movementCostMultiplier({ x: 0, y: 0 }), 1.5);
  }

  test_unset_values_fall_back() {
    const stats = new TerrainStats({ "0,0": {} });
    this.assertApprox(stats.populationMultiplier({ x: 0, y: 0 }), 0.0);
-    this.assertApprox(stats.gdpMultiplier({ x: 0, y: 0 }), 0.0);
+    this.assertApprox(stats.productionMultiplier({ x: 0, y: 0 }), 0.0);
    this.assertApprox(stats.movementCostMultiplier({ x: 0, y: 0 }), DEFAULT_MOVEMENT_COST_MULTIPLIER);
  }

@@ -48,7 +48,7 @@ export class TerrainStatsTest extends TestCase {
    this.assertNotEmpty(land);
    for (const tile of land) {
      this.assertHas(tile, "populationMultiplier");
-      this.assertHas(tile, "gdpMultiplier");
+      this.assertHas(tile, "productionMultiplier");
      this.assertHas(tile, "movementCostMultiplier");
    }
    const cheapest = Math.min(...TERRAIN_TILES.map((t) => t.movementCostMultiplier || DEFAULT_MOVEMENT_COST_MULTIPLIER));
@@ -1,5 +1,5 @@
 import { TestCase } from "./framework/test_case.js";
-import { smallState, cityOf } from "./framework/helpers.js";
+import { smallState, cityOf, stripPorts } from "./framework/helpers.js";
 import { key } from "../shared/hex.js";
 import { TRENCH } from "../shared/data/combat.js";

@@ -47,6 +47,8 @@ export class TrenchTest extends TestCase {

  test_trenches_multiply_defense_and_cut_gdp() {
    const state = smallState();
+    // A seeded port adds flat GDP that the trench multiplier would not scale.
+    stripPorts(state, 0);
    const coords = ownLand(state);
    const k = key(coords.x, coords.y);
    const before = state.getTileGdpPerCapita(coords);
@@ -54,7 +56,7 @@ export class TrenchTest extends TestCase {
    state._gdpPerCapitaCache.delete(k);
    this.assertApprox(
      state.getTileGdpPerCapita(coords),
-      before * TRENCH.gdpMultiplier,
+      before * TRENCH.productionMultiplier,
      1e-6,
      "a trench costs the tile a fifth of its GDP per capita"
    );
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