No deep ore in rock hot enough to light or melt it; reloaded worlds settle again (t3)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/DESIGN.md

@@ -240,6 +240,10 @@ above, including:
     their price). The top quarter of the underground is unchanged; copper also forms in deep stone
     and granite, coal in basalt, tin deeper. Lenses grow from lower noise thresholds only:
     stretching the noise with depth sheared it into diagonal streaks.
+    No ore is placed where the natural rock temperature would light it (coal) or melt it (metal
+    ores, within 200°C): deep coal and gold next to the magma burned and ran forever once a
+    reload woke those areas, and a Huge world dropped to about 10 fps. So deep coal stays in a
+    cooler mid band, and coal is about 3.2x rather than 5x; total ore about 4.2x.
   - Waste rock pays: grinding granite and basalt finds about twice the ore, and builders order
     granite and basalt rubble in bulk.
   - A Huge size (6144 x 2048); saves are gzip-compressed (a Medium save went from 29 MB to 0.4 MB).

docs/PROJECT_MAP.md

@@ -324,7 +324,7 @@ Weather: clouds from steam, rain and snow, and the world water count.
 simTick: one simulation step, in order.
 - functions: simTick
 
-### src/sim/worldgen.js (322 lines)
+### src/sim/worldgen.js (326 lines)
 World generation: noise, layers, ores, caves, water, trees, and clearing tiny hard specks.
 - functions: makeNoise, fbm, clearHardSpecks, generateWorld
 - variables: SPECK_MIN

docs/agent-log.md

@@ -4,6 +4,19 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-24: t3 fix: deep ore burned and melted after a reload (Claude Code)
+
+- Owner: a Huge world ran at about 10 fps after travelling between claims, even after a refresh.
+  Cause: reloading wakes every area, and t3's deep coal (ignites at 430°C, natural rock reaches
+  that at about 70% depth) and gold next to the magma burned and melted forever: about 2,100 of
+  12,288 areas stayed busy, 65 ms per tick. A fresh world hid it because nothing deep was awake.
+- `worldgen.js`: an ore is not placed where `AMB[y]` is within 120°C of its ignition or 200°C of
+  its melting point; a cooler coal band in stone and granite at 45%+ depth replaces most of the
+  lost coal. Huge after a reload: 335 areas awake, about 5 ms per tick; Medium 104 (126 before
+  t3). Medium seed 424242 ore is now about 4.2x the original (coal 3.2x, gold 2.8x).
+- `test/t_world.js`: no ore in too-hot rock; a reloaded world settles with no fires and under
+  10% of areas moving; ore balance ranges updated. Existing saves made with the bug keep it.
+
 ## 2026-10-24: t3: a world that lasts (Claude Code, Codex)
 
 - `26d17c2` deeper is richer (`worldgen.js` ore thresholds drop with depth below fy 0.25).