Marching into unexplored or enemy land reveals a tile every step, and each
reveal rebuilt the whole-map fog mesh: about 1.8M vertices and 50 MB on a
160x160 map, regenerated at the rebuild throttle. Walking through
already-explored home land reveals nothing, which is why the stutter only
showed up on a border crossing, with a single unit.
- buildKnowledge now takes a row range and builds only the rows on screen; the
row table stays full length so the existing row-banded draw keeps working.
- _flushFog rebuilds on a visibility change or a pan to a new row band, still
coalesced, and the draw clamps to the band that was built.
- A mode/zoom change schedules the band rebuild instead of building the whole
mesh, and uniform interior tiles skip the per-vertex blur kernel.
adrien
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