Docs: the snapping sound confirmed in the owner's world (water boiling on hot deep rock)

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

docs/DESIGN.md

@@ -180,8 +180,9 @@ above, including:
 - **World sounds are local.** Sounds from the world (water sizzling on hot metal or lava, and
   any other event with a place) fade with distance from the view and pan left or right; they go
   silent one screen width off-screen. The owner heard a constant snapping that followed the bot
-  in an older world but not in a new one. Most likely the sizzle: in a test, a lava and water
-  contact far from the bot sizzled about 580 times a minute, all played at full volume.
+  in an older world but not in a new one. It was the sizzle: in the owner's world, water that
+  had found its way down to hot basalt and granite (480-800°C, about 500 grains below the
+  surface) boiled about 48 times a minute, and every sizzle played at full volume.
 
 - **The silo has pixel art in the pixel look**, drawn grain by grain like the rest of the world;
   the smooth look keeps the illustrated silo. The owner noticed it looked the same in both.

docs/agent-log.md

@@ -35,7 +35,10 @@ effects are not local?" The owner then confirmed a new world is quiet.
   `docs/DESIGN.md`, `docs/PROJECT_MAP.md`.
 - `test/play.py`: far off-screen is silent, on screen plays, just off-screen is quieter and
   panned. All 11 headless suites, `play.py` and `t_smooth.py` pass.
-- Open: not tested against the owner's own save; the owner checks by ear.
+- Checked afterwards with the owner's exported world (seed 622525): over one minute, 48 sizzles
+  and no other sounds, all from water boiling on naturally hot deep rock (a pool on 580°C basalt
+  and drips in a shaft and a cave, about 500 grains below the bot). Nothing built there. With
+  the fix every one of them is silent from the surface.
 
 ## 2026-10-23: fewer, smaller messages (Claude Code, with Codex)