Fog of war: unexplored is black, fades ease into it with no stepped rim (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: no jagged rim, unexplored is black (Claude Code)
+
+- The owner still saw a jagged grey edge. Causes found by sampling pixels: the fade went to 0
+  (black) while unexplored was drawn (12, 10, 10), leaving a dark stepped rim; the ±40 noise lit
+  the faintest cells; rays that reached rock already dim dropped to 0 in 2–3 grains.
+- `src/render/world.js`: unexplored and off-map are pure black (`OUT`, smooth-look buffers);
+  partial fog eases into black along a smoothstep, with noise scaled by s·(1−s). `src/sim/fog.js`:
+  sight into rock fades over 8 grains as a fraction of its brightness.
+- `test/play.py`: the three unexplored-colour checks expect black (owner's decision).
+  `docs/systems/fog.md` updated. Screenshots `shots/fog-dig-black-{pixel,smooth,nolight}.png`.
+- Tests: `run_all.py --browser` passed except `t_smooth` once at load 7 (passed on rerun).
+
 ## 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