Derived every description figure from the rule it describes

AGENTS.md

@@ -89,7 +89,14 @@ There is no linter, formatter, or CI. Do not invent commands beyond these.
   simulation: they surface in tooltips — city building cards and resource
   producers (`client/js/ui/card.js` `tooltipSections`), spy operations and
   minority policies (`game_screen/panels.js`, `modals/nation.js`) — so correct
-  them when the behaviour they describe changes.
+  them when the behaviour they describe changes. Never type a figure into that
+  prose: interpolate the field or constant the simulation uses (a
+  `get description()`/`get targetEffect()`, not a literal), and render it with
+  the shared formatters so the description quotes exactly what the game shows.
+  The amount formatters live in `shared/data/resources.js` (`formatEnergy`,
+  `formatResourceAmount`, re-exported by `shared/resources.js`); `text_format.js`
+  has `formatNumber`/`formatPercent`. `tests/descriptions_test.js` recomputes each
+  figure and fails when the prose drifts from its source.
 - Keep aircraft out of the melee: `_battleTiles`/`_combatTarget` skip them and
   their strikes are routed explicitly. Mirror the air rules (airport-only
   rebasing, strike radius, ferry fuel) on both client and server, or prediction

client/js/devlog_data.js

@@ -1,6 +1,12 @@
 // Generated by scripts/generate-devlog.js from `git log`; do not edit.
 // The pre-commit hook refreshes it so the main menu shows the latest commits.
 export const DEVLOG = [
+  {
+    "hash": "c85f79f",
+    "date": "2026-09-27",
+    "subject": "Drew one bombardment arc per stack above the unit icons",
+    "body": ""
+  },
   {
     "hash": "4d3591c",
     "date": "2026-09-27",
@@ -54,11 +60,5 @@ export const DEVLOG = [
     "date": "2026-09-24",
     "subject": "Flew aircraft and missiles straight and let strikes target fogged cities",
     "body": ""
-  },
-  {
-    "hash": "36ac669",
-    "date": "2026-09-24",
-    "subject": "Let stacks split by shift-click and cross allied or at-war land",
-    "body": ""
   }
 ];

shared/data/buildings.js

@@ -3,6 +3,13 @@
 // the level too.
 
 import { EFFECT_PRODUCTION, EFFECT_RESEARCH, EFFECT_CULTURE, effect } from "./effects.js";
+import { formatNumber, formatPercent } from "../text_format.js";
+import { AIR_DEFENSE } from "./combat.js";
+import { SATELLITE } from "./intelligence.js";
+
+// Extra production lines a barracks or shipyard level adds. Shared by the
+// simulation and the descriptions so the two never disagree.
+export const PARALLEL_LINES_PER_LEVEL = 1;
 
 // 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.
@@ -29,7 +36,9 @@ export const BUILDINGS = [
   {
     id: "barracks",
     name: "Barracks",
-    description: "Enables training infantry units. Each level allows one more parallel training.",
+    get description() {
+      return `Enables training infantry units. Each level allows ${PARALLEL_LINES_PER_LEVEL} more parallel training.`;
+    },
     baseCost: 10_000_000,
     costAlpha: 1.1,
     refundFraction: 0.5,
@@ -40,7 +49,9 @@ export const BUILDINGS = [
   {
     id: "shelters",
     name: "Wartime shelters",
-    description: "Each level shelters another 10% of the city's people from bombing, up to all of them. Extremely hard to destroy. Does not protect other buildings.",
+    get description() {
+      return `Each level shelters another ${formatPercent(this.civilianProtectionPerLevel)} of the city's people from bombing, up to all of them. Extremely hard to destroy. Does not protect other buildings.`;
+    },
     baseCost: 100_000_000,
     costAlpha: 2,
     refundFraction: 0.5,
@@ -58,7 +69,9 @@ export const BUILDINGS = [
     id: "aa_building",
     advanced: true,
     name: "Air defense",
-    description: "Fires on hostile aircraft and missiles that come within two tiles of this city.",
+    get description() {
+      return `Fires on hostile aircraft and missiles that come within ${AIR_DEFENSE.rangeTiles} tiles of this city.`;
+    },
     baseCost: 1_000_000_000,
     costAlpha: 2,
     refundFraction: 0.5,
@@ -114,7 +127,9 @@ export const BUILDINGS = [
   {
     id: "port",
     name: "Port",
-    description: "Warm water port. Adds 1000 production per person per adjacent sea tile per level, and brings in extra food.",
+    get description() {
+      return `Warm water port. Adds ${formatNumber(this.productionPerSeaTilePerLevel)} production per person per adjacent sea tile per level, and brings in extra food.`;
+    },
     baseCost: 20_000_000,
     costAlpha: 1.7,
     refundFraction: 0.5,
@@ -144,7 +159,9 @@ export const BUILDINGS = [
   {
     id: "shipyard",
     name: "Shipyard",
-    description: "Naval yards that build warships. Only a coastal city can raise one, and it must already have a port. Each level adds one parallel building queue.",
+    get description() {
+      return `Naval yards that build warships. Only a coastal city can raise one, and it must already have a port. Each level adds ${PARALLEL_LINES_PER_LEVEL} parallel building queue.`;
+    },
     baseCost: 150_000_000,
     costAlpha: 1.65,
     refundFraction: 0.5,
@@ -172,7 +189,9 @@ export const BUILDINGS = [
     id: "space_launch_center",
     advanced: true,
     name: "Space launch centre",
-    description: "A rocket complex. Each level lets the nation launch one spy satellite, which uncovers a random patch of the world every two days. Extremely expensive.",
+    get description() {
+      return `A rocket complex. Each level lets the nation launch ${SATELLITE.perLaunchCentreLevel} spy satellite, which uncovers a random patch of the world every ${SATELLITE.revealEveryDays} days. Extremely expensive.`;
+    },
     baseCost: 10_000_000_000,
     costAlpha: 2,
     refundFraction: 0.5,

shared/data/improvements.js

@@ -63,8 +63,9 @@ 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.",
+    get description() {
+      return `Watches ${this.vision} tiles out. A ranged hit damages it and an enemy walking onto it captures it.`;
+    },
     buildCost: 60_000_000,
     maintenance: 1000,
     vision: 5,
@@ -76,8 +77,9 @@ export const TILE_IMPROVEMENTS = [
     id: "coastal_cannon",
     advanced: true,
     name: "Coastal cannon",
-    description:
-      "Automatically fires on hostile naval units within two tiles. Only a coastal tile can carry one.",
+    get description() {
+      return `Automatically fires on hostile naval units within ${this.range} tiles. Only a coastal tile can carry one.`;
+    },
     buildCost: 120_000_000,
     maintenance: 2000,
     range: 2,

shared/data/intelligence.js

@@ -53,9 +53,12 @@ export const ESPIONAGE = {
 
 // Spy satellites: a launch is free once the (very expensive) space launch centre
 // stands, and each satellite uncovers a random patch of the world on a cadence.
+// A centre sustains this many satellites for every level it has, one each by
+// default.
 export const SATELLITE = {
   revealEveryDays: 2,
   revealRadius: 2,
+  perLaunchCentreLevel: 1,
 };
 
 // `description` is the reference text the Intelligence tab shows, not a
@@ -72,8 +75,9 @@ export const SPY_OPERATIONS = [
   {
     id: SPY_SABOTAGE,
     name: "Sabotage",
-    description:
-      "Cripple a tile's production for a week. The act may be pinned on another nation, or on no one at all. Spends the spies.",
+    get description() {
+      return `Cripple a tile's production for ${SABOTAGE.blockDays} days. The act may be pinned on another nation, or on no one at all. Spends the spies.`;
+    },
   },
   {
     id: SPY_CITY,

shared/data/politics.js

@@ -56,6 +56,18 @@ export const POPULARITY = {
   pillage: 6,
 };
 
+// An opinion shift as the integer popularity points the policies are quoted in,
+// so the wizard's estimates come straight from the applied effect.
+export function opinionToPoints(opinion) {
+  return Math.round(opinion / POPULARITY.opinionPerPoint);
+}
+
+// A signed popularity figure with the typographic minus the catalogue uses.
+function popularityPointsText(opinion) {
+  const points = opinionToPoints(opinion);
+  return `${points < 0 ? "\u2212" : "+"}${Math.abs(points)}`;
+}
+
 // A campaign costs nothing to start: it charges `defaultHourlyCost` for as long
 // as it runs, like any other upkeep and shown in the budget. The player may
 // raise or lower the spending up to `maxHourlyCost`; the opinion shift scales
@@ -102,16 +114,24 @@ export const POLICIES = [
     name: "Champion a minority",
     description:
       "Proclaim the state the protector of an ethnicity. Its people everywhere warm to you, but your own other populations resent the favouritism.",
-    targetEffect: "+30 popularity among the chosen people",
-    politicalCost: "−16 popularity among every other population in your country",
+    get targetEffect() {
+      return `${popularityPointsText(POLICY_OPINION.championTarget)} popularity among the chosen people`;
+    },
+    get politicalCost() {
+      return `${popularityPointsText(POLICY_OPINION.championMajority)} popularity among every other population in your country`;
+    },
   },
   {
     id: POLICY_PROTECT,
     name: "Protect a minority",
     description:
       "Shield an ethnicity inside your borders. It raises their view of you at home and abroad, at some cost with your other populations.",
-    targetEffect: "+24 popularity among the chosen people",
-    politicalCost: "−8 popularity among every other population in your country",
+    get targetEffect() {
+      return `${popularityPointsText(POLICY_OPINION.protectTarget)} popularity among the chosen people`;
+    },
+    get politicalCost() {
+      return `${popularityPointsText(POLICY_OPINION.protectMajority)} popularity among every other population in your country`;
+    },
   },
   {
     id: POLICY_EXPEL,
@@ -119,7 +139,9 @@ export const POLICIES = [
     description:
       "Force an ethnicity out of the country. Its people, in and outside your borders, will hate you for a long time, and they will press into your neighbours.",
     targetEffect: "The people begin to leave for neighbouring countries",
-    politicalCost: "−80 popularity among the expelled people, remembered for a generation",
+    get politicalCost() {
+      return `${popularityPointsText(POLICY_OPINION.expelTarget)} popularity among the expelled people, remembered for a generation`;
+    },
   },
   {
     id: POLICY_IMMIGRATION,
@@ -127,7 +149,9 @@ export const POLICIES = [
     description:
       "Invite an ethnicity in. They will come from lands where their government is unpopular, but every other population in your country dislikes the influx.",
     targetEffect: "The chosen people migrate into your country",
-    politicalCost: "−10 popularity among every other population in your country",
+    get politicalCost() {
+      return `${popularityPointsText(POLICY_OPINION.immigrationOthers)} popularity among every other population in your country`;
+    },
   },
 ];
 

shared/data/resources.js

@@ -13,6 +13,7 @@ import {
   EFFECT_LUXURY_EFFICIENCY,
   EFFECT_HIGHTECH_EFFICIENCY,
 } from "./effects.js";
+import { groupDigits } from "../text_format.js";
 
 // Energy is stored and moved as kWh. These keep the catalogue readable.
 export const KWH_PER_MWH = 1_000;
@@ -112,6 +113,35 @@ export function resourceById(id) {
   return RESOURCES[RESOURCE_INDEX[id]] || null;
 }
 
+// --------------------------------------------------------------- formatting --
+//
+// The canonical rendering of an amount, shared with the browser so a
+// description quotes exactly what the game shows. Energy reads in kWh, MWh,
+// GWh or TWh; a material in its own unit, stepping through kt/Mt, kct and ku.
+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`;
+}
+
+export function formatResourceAmount(id, value) {
+  if (id === "energy") return formatEnergy(value);
+  const amount = Math.max(0, value);
+  const unit = resourceById(id) ? resourceById(id).unit : "";
+  if (amount >= 1e12) return `${trim(amount / 1e12)} T${unit}`;
+  if (amount >= 1e9) return `${trim(amount / 1e9)} G${unit}`;
+  if (amount >= 1e6) return `${trim(amount / 1e6)} M${unit}`;
+  return `${trim(amount)} ${unit}`;
+}
+
+function trim(value) {
+  if (value >= 100) return groupDigits(Math.round(value));
+  if (value >= 10) return value.toFixed(1).replace(/\.0$/, "");
+  return value.toFixed(2).replace(/\.?0+$/, "");
+}
+
 // 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
@@ -310,8 +340,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "coal_power_plant",
     name: "Coal power plant",
-    description:
-      "Burns coal to make 2,500 GWh of electricity a day. Cheap to raise, but the fuel bill never stops.",
+    get description() {
+      return `Burns coal to make ${formatEnergy(this.outputPerDay)} 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,
@@ -323,8 +354,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "natural_gas_power_plant",
     name: "Natural gas power plant",
-    description:
-      "The cleanest fossil plant: 3,000 GWh a day for a higher fuel bill.",
+    get description() {
+      return `The cleanest fossil plant: ${formatEnergy(this.outputPerDay)} a day for a higher fuel bill.`;
+    },
     resource: "energy",
     outputPerDay: 300 * KWH_PER_GWH,
     fuelEnergyPerDay: 300 * KWH_PER_GWH * 0.25,
@@ -336,7 +368,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "oil_power_plant",
     name: "Oil power plant",
-    description: "Burns oil for 2,700 GWh of electricity a day.",
+    get description() {
+      return `Burns oil for ${formatEnergy(this.outputPerDay)} of electricity a day.`;
+    },
     resource: "energy",
     outputPerDay: 270 * KWH_PER_GWH,
     fuelEnergyPerDay: 270 * KWH_PER_GWH * 0.25,
@@ -348,8 +382,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "solar_power_plant",
     name: "Solar power plant",
-    description:
-      "A field of panels producing a steady 300 GWh a day with no fuel and no upkeep.",
+    get description() {
+      return `A field of panels producing a steady ${formatEnergy(this.outputPerDay)} a day with no fuel and no upkeep.`;
+    },
     resource: "energy",
     outputPerDay: 30 * KWH_PER_GWH,
     energyPerDay: 0,
@@ -361,7 +396,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "geothermal_plant",
     name: "Geothermal plant",
-    description: "Taps the earth's heat for 600 GWh a day of free electricity.",
+    get description() {
+      return `Taps the earth's heat for ${formatEnergy(this.outputPerDay)} a day of free electricity.`;
+    },
     resource: "energy",
     outputPerDay: 60 * KWH_PER_GWH,
     energyPerDay: 0,
@@ -373,7 +410,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "wind_turbines",
     name: "Wind turbines",
-    description: "A hilltop wind farm making 250 GWh a day for free.",
+    get description() {
+      return `A hilltop wind farm making ${formatEnergy(this.outputPerDay)} a day for free.`;
+    },
     resource: "energy",
     outputPerDay: 25 * KWH_PER_GWH,
     energyPerDay: 0,
@@ -385,7 +424,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "offshore_wind_turbines",
     name: "Offshore wind turbines",
-    description: "Turbines out at sea making 500 GWh a day. Needs a coastal tile.",
+    get description() {
+      return `Turbines out at sea making ${formatEnergy(this.outputPerDay)} a day. Needs a coastal tile.`;
+    },
     resource: "energy",
     outputPerDay: 50 * KWH_PER_GWH,
     energyPerDay: 0,
@@ -399,7 +440,9 @@ export const RESOURCE_BUILDINGS = [
     id: "fusion_power_plant",
     advanced: true,
     name: "Fusion power plant",
-    description: "A late-game reactor producing 40 TWh of electricity a day.",
+    get description() {
+      return `A late-game reactor producing ${formatEnergy(this.outputPerDay)} of electricity a day.`;
+    },
     resource: "energy",
     outputPerDay: 4_000 * KWH_PER_GWH,
     energyPerDay: 0,
@@ -416,8 +459,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "steel_mill",
     name: "Steel mill",
-    description:
-      "Smelts iron into 200,000 t of steel a day, spending 20 MWh of energy per tonne.",
+    get description() {
+      return `Smelts iron into ${formatResourceAmount(this.resource, this.outputPerDay)} of steel a day, spending ${formatEnergy(RESOURCE_RULES.energyPerSteelTonne)} of energy per tonne.`;
+    },
     resource: "steel",
     outputPerDay: 20_000,
     energyPerDay: 2_000 * RESOURCE_RULES.energyPerSteelTonne,
@@ -428,7 +472,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "gold_mine",
     name: "Gold mine",
-    description: "Produces 200,000 carats of luxury a day, at 10 MWh a carat.",
+    get description() {
+      return `Produces ${formatResourceAmount(this.resource, this.outputPerDay)} of luxury a day, at ${formatEnergy(RESOURCE_RULES.energyPerLuxuryCarat.gold_mine)} a carat.`;
+    },
     resource: "luxury",
     outputPerDay: 20_000,
     energyPerDay: 20_000 * RESOURCE_RULES.energyPerLuxuryCarat.gold_mine,
@@ -439,7 +485,9 @@ export const RESOURCE_BUILDINGS = [
   {
     id: "diamond_mine",
     name: "Diamond mine",
-    description: "Produces 200,000 carats of luxury a day, at 5 MWh a carat.",
+    get description() {
+      return `Produces ${formatResourceAmount(this.resource, this.outputPerDay)} of luxury a day, at ${formatEnergy(RESOURCE_RULES.energyPerLuxuryCarat.diamond_mine)} a carat.`;
+    },
     resource: "luxury",
     outputPerDay: 20_000,
     energyPerDay: 20_000 * RESOURCE_RULES.energyPerLuxuryCarat.diamond_mine,
@@ -451,8 +499,9 @@ export const RESOURCE_BUILDINGS = [
     id: "chip_foundry",
     advanced: true,
     name: "Chip foundry",
-    description:
-      "Fabricates 50,000 units of high-tech a day, spending 10 MWh of energy per unit.",
+    get description() {
+      return `Fabricates ${formatResourceAmount(this.resource, this.outputPerDay)} of high-tech a day, spending ${formatEnergy(RESOURCE_RULES.energyPerHighTechUnit)} of energy per unit.`;
+    },
     resource: "hightech",
     outputPerDay: 5_000,
     energyPerDay: 5_000 * RESOURCE_RULES.energyPerHighTechUnit,

shared/data/statuses.js

@@ -7,6 +7,8 @@
 // each day), a `cityHpLossPerDay` override for when the unit stands in a city,
 // and an `upkeepMultiplier` applied to the unit's upkeep while it is active.
 
+import { formatPercent } from "../text_format.js";
+
 export const STATUS_ENCIRCLED = "encircled";
 export const STATUS_BESIEGED = "besieged";
 export const STATUS_BATTLE = "battle";
@@ -16,7 +18,9 @@ export const STATUSES = [
     id: STATUS_ENCIRCLED,
     label: "Encircled",
     icon: "encirclement.svg",
-    description: "Cut off: every adjacent land tile is held by a hostile unit and no friendly port supplies it by sea. Loses 10% of its maximum hit points each day, or 2% inside a city.",
+    get description() {
+      return `Cut off: every adjacent land tile is held by a hostile unit and no friendly port supplies it by sea. Loses ${formatPercent(this.hpLossPerDay)} of its maximum hit points each day, or ${formatPercent(this.cityHpLossPerDay)} inside a city.`;
+    },
     hpLossPerDay: 0.10,
     cityHpLossPerDay: 0.02,
   },
@@ -30,7 +34,9 @@ export const STATUSES = [
     id: STATUS_BATTLE,
     label: "In battle",
     icon: "icon_battle.svg",
-    description: "Fighting an enemy unit on the same tile. Upkeep is tripled and the unit cannot pillage while the battle rages.",
+    get description() {
+      return `Fighting an enemy unit on the same tile. Upkeep is multiplied by ${this.upkeepMultiplier} and the unit cannot pillage while the battle rages.`;
+    },
     upkeepMultiplier: 3,
   },
 ];

shared/game_state/economy.js

@@ -11,7 +11,7 @@ import {
   EFFECT_RAIL_SPEED,
 } from "../data/effects.js";
 import { CITY_GARRISON_HEAL_PER_HOUR } from "../data/combat.js";
-import { BUILDING_MECHANIC } from "../data/buildings.js";
+import { BUILDING_MECHANIC, PARALLEL_LINES_PER_LEVEL } from "../data/buildings.js";
 import { technologyCost, technologyById } from "../data/technologies.js";
 import { NEWS_TECHNOLOGY } from "../data/relations.js";
 import {
@@ -1099,8 +1099,8 @@ export const economyMethods = {
       // (units) and Shipyards (buildings) add. Each line works one entry at full
       // capacity, so a higher-level city produces several things at once; the
       // overflow of a finished entry carries into the next waiting one.
-      const unitLines = 1 + this._cityMechanicLevel(city, BUILDING_MECHANIC.PARALLEL_TRAINING);
-      const buildingLines = 1 + this._cityMechanicLevel(city, BUILDING_MECHANIC.PARALLEL_BUILDING);
+      const unitLines = 1 + PARALLEL_LINES_PER_LEVEL * this._cityMechanicLevel(city, BUILDING_MECHANIC.PARALLEL_TRAINING);
+      const buildingLines = 1 + PARALLEL_LINES_PER_LEVEL * this._cityMechanicLevel(city, BUILDING_MECHANIC.PARALLEL_BUILDING);
       this._advanceProduction(queue, city, "unit", unitLines);
       this._advanceProduction(queue, city, "building", buildingLines);
       if (queue.length === 0) completed.push(cityId);

shared/game_state/intelligence.js

@@ -330,7 +330,7 @@ export const intelligenceMethods = {
       for (const [index, level] of Object.entries(city.buildings || {})) {
         const proto = this.protoBuildings[index];
         if (proto && proto.mechanic === BUILDING_MECHANIC.SPACE_LAUNCH) {
-          total += Number(level) || 0;
+          total += (Number(level) || 0) * SATELLITE.perLaunchCentreLevel;
         }
       }
     }

shared/resources.js

@@ -8,42 +8,16 @@ import {
   RESOURCE_RULES,
   RESOURCE_MARKET,
   RESOURCE_MARKET_BASE,
-  resourceById,
+  formatEnergy,
+  formatResourceAmount,
 } from "./data/resources.js";
 import { EFFECT_RESEARCH } from "./data/effects.js";
-import { groupDigits } from "./text_format.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. The prefix and the divisor move
-// together, so a million tonnes reads as 1 Mt rather than 1 kt.
-export function formatResourceAmount(id, value) {
-  if (id === "energy") return formatEnergy(value);
-  const amount = Math.max(0, value);
-  const unit = resourceById(id) ? resourceById(id).unit : "";
-  if (amount >= 1e12) return `${trim(amount / 1e12)} T${unit}`;
-  if (amount >= 1e9) return `${trim(amount / 1e9)} G${unit}`;
-  if (amount >= 1e6) return `${trim(amount / 1e6)} M${unit}`;
-  return `${trim(amount)} ${unit}`;
-}
-
-function trim(value) {
-  if (value >= 100) return groupDigits(Math.round(value));
-  if (value >= 10) return value.toFixed(1).replace(/\.0$/, "");
-  return value.toFixed(2).replace(/\.?0+$/, "");
-}
+// The amount formatters live with the resource catalogue so its descriptions
+// can quote the same figures; re-exported here for the existing callers.
+export { formatEnergy, formatResourceAmount };
 
 // --------------------------------------------------------------- per-person --
 

shared/text_format.js

@@ -69,6 +69,16 @@ export function compact(value) {
   return sign + text + suffixes[index];
 }
 
+// A fraction as a whole-number percentage, the unit most descriptions quote:
+// 0.1 reads "10%". Callers pass the raw fraction the simulation applies so a
+// description can never drift from the rule it describes.
+export function formatPercent(fraction, { decimals = 0 } = {}) {
+  const value = Number(fraction) * 100;
+  const fixed = value.toFixed(decimals);
+  const text = decimals === 0 ? fixed : fixed.replace(/\.?0+$/, "");
+  return `${text}%`;
+}
+
 export function improvements(list) {
   if (!list || list.length === 0) return "None";
   return list.join(", ");

tests/descriptions_test.js

@@ -0,0 +1,121 @@
+import { TestCase } from "./framework/test_case.js";
+import {
+  RESOURCE_BUILDINGS,
+  RESOURCE_RULES,
+  TILE_IMPROVEMENTS,
+  STATUSES,
+  POLICY_OPINION,
+  opinionToPoints,
+  SPY_OPERATIONS,
+  AIR_DEFENSE,
+  SATELLITE,
+  SABOTAGE,
+  PARALLEL_LINES_PER_LEVEL,
+  buildingById,
+  policyById,
+} from "../shared/data.js";
+import { formatEnergy, formatResourceAmount } from "../shared/resources.js";
+import { formatNumber, formatPercent } from "../shared/text_format.js";
+
+// Every figure a description quotes must be derived from the same field the
+// simulation applies, never typed in. These tests recompute the figure and
+// assert the description shows it, so a rule change that leaves the prose stale
+// fails here.
+export class DescriptionsTest extends TestCase {
+  test_resource_building_descriptions_quote_their_output() {
+    for (const proto of RESOURCE_BUILDINGS) {
+      const output = formatResourceAmount(proto.resource, proto.outputPerDay);
+      this.assertTrue(
+        proto.description.includes(output),
+        `${proto.id} should quote ${output}: ${proto.description}`
+      );
+    }
+  }
+
+  test_material_producer_descriptions_quote_their_energy_ratio() {
+    const ratios = {
+      steel_mill: RESOURCE_RULES.energyPerSteelTonne,
+      gold_mine: RESOURCE_RULES.energyPerLuxuryCarat.gold_mine,
+      diamond_mine: RESOURCE_RULES.energyPerLuxuryCarat.diamond_mine,
+      chip_foundry: RESOURCE_RULES.energyPerHighTechUnit,
+    };
+    for (const [id, ratio] of Object.entries(ratios)) {
+      const proto = RESOURCE_BUILDINGS.find((b) => b.id === id);
+      const energy = formatEnergy(ratio);
+      this.assertTrue(
+        proto.description.includes(energy),
+        `${id} should quote ${energy} per unit: ${proto.description}`
+      );
+    }
+  }
+
+  test_building_descriptions_quote_their_rules() {
+    const shelters = buildingById("shelters");
+    const protection = formatPercent(shelters.civilianProtectionPerLevel);
+    this.assertTrue(shelters.description.includes(protection), `shelters quote ${protection}`);
+
+    const air = buildingById("aa_building");
+    this.assertTrue(air.description.includes(`${AIR_DEFENSE.rangeTiles} tiles`), "air defense range");
+
+    const port = buildingById("port");
+    const production = formatNumber(port.productionPerSeaTilePerLevel);
+    this.assertTrue(port.description.includes(production), `port quote ${production}`);
+
+    const space = buildingById("space_launch_center");
+    this.assertTrue(space.description.includes(`${SATELLITE.revealEveryDays} days`), "satellite cadence");
+    this.assertTrue(
+      space.description.includes(String(SATELLITE.perLaunchCentreLevel)),
+      "satellites per centre level"
+    );
+
+    for (const id of ["barracks", "shipyard"]) {
+      const proto = buildingById(id);
+      this.assertTrue(
+        proto.description.includes(String(PARALLEL_LINES_PER_LEVEL)),
+        `${id} quotes ${PARALLEL_LINES_PER_LEVEL} line(s)`
+      );
+    }
+  }
+
+  test_improvement_descriptions_quote_their_range() {
+    for (const [id, field] of [["radar_tower", "vision"], ["coastal_cannon", "range"]]) {
+      const proto = TILE_IMPROVEMENTS.find((i) => i.id === id);
+      this.assertTrue(
+        proto.description.includes(String(proto[field])),
+        `${id} quotes its ${field} (${proto[field]})`
+      );
+    }
+  }
+
+  test_status_descriptions_quote_their_effect() {
+    const encircled = STATUSES.find((s) => s.id === "encircled");
+    this.assertTrue(encircled.description.includes(formatPercent(encircled.hpLossPerDay)));
+    this.assertTrue(encircled.description.includes(formatPercent(encircled.cityHpLossPerDay)));
+
+    const battle = STATUSES.find((s) => s.id === "battle");
+    this.assertTrue(battle.description.includes(String(battle.upkeepMultiplier)));
+  }
+
+  test_policy_effects_quote_their_opinion_shift() {
+    const expected = [
+      ["champion", "championTarget", "targetEffect"],
+      ["champion", "championMajority", "politicalCost"],
+      ["protect", "protectTarget", "targetEffect"],
+      ["protect", "protectMajority", "politicalCost"],
+      ["expel", "expelTarget", "politicalCost"],
+      ["immigration", "immigrationOthers", "politicalCost"],
+    ];
+    for (const [id, field, slot] of expected) {
+      const points = opinionToPoints(POLICY_OPINION[field]);
+      this.assertTrue(
+        policyById(id)[slot].includes(String(Math.abs(points))),
+        `${id}.${slot} should quote ${Math.abs(points)} points`
+      );
+    }
+  }
+
+  test_spy_operation_descriptions_quote_their_block() {
+    const sabotage = SPY_OPERATIONS.find((op) => op.id === "sabotage");
+    this.assertTrue(sabotage.description.includes(`${SABOTAGE.blockDays} days`));
+  }
+}