Fog of war: wider fades and a grainy edge instead of stepped lines (t17)

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

docs/agent-log.md

@@ -4,6 +4,18 @@ 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: t17 follow-up: softer fog edges (Claude Code, Codex)
+
+- The owner found the edges sharp and stepped. `src/sim/fog.js`: sense ring 24 grains with a
+  12-grain fade (`FOG_SENSE_FADE`), rays fade 8 grains into rock and over the last 16 of range,
+  surface fade 16, `fogRevealAround` gets a 6-grain soft edge. `src/render/world.js`: partly seen
+  grains get ±40 of per-grain noise (`noiseB`), so edges look grainy, not stepped.
+- `test/t_fog.js`: a point in the fade band is between 0 and 128. `docs/systems/fog.md` updated.
+  Screenshots `shots/fog-edge-{before,after}{,-nolight}.png` compared.
+- Tests: all pass except `t_smooth` half-resolution, which failed 1 of 3 runs with the change and
+  passed 2 of 2 without, at load 6–12; that check runs with fog off, so the drawing change does
+  not run there. Fog drawing 0.43 → 0.45 ms.
+
 ## 2026-10-24: t17 Fog of war reveals the ground around the bot (Claude Code, Codex)
 
 - `src/sim/fog.js`: `FOG_SENSE = 20`; `fogLook` also reveals every fog cell within 20 grains,