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/DESIGN.md

@@ -237,6 +237,8 @@ above, including:
 - **Fog of war also reveals the ground around the bot (t17, 2026-10-24).** About 20 grains in every
   direction, through rock, fully clear with a soft edge. Line of sight alone hid everything inside
   the ground, so the owner couldn't see what was around them or where to dig.
+  As tuned: clear to 12 grains, fading out by 24, with a grainy edge; the owner found the first
+  version's narrow fade too sharp.
 
 ## Ideas not built yet
 

docs/PROJECT_MAP.md

@@ -221,10 +221,10 @@ World state: the per-cell typed arrays, alloc(), ambient temperature by depth, w
 - functions: emit, bagCap, discover, alloc, depthU, depthY, computeAmbient, fillNoise, wakeXY, wakeHeatXY, wakeIdx, wakeHeatIdx
 - variables: W, H, N, CW, CH, NCH, mat, temp, life, flags, stamp, part, mach, digp, noiseB, airS, netId, isPow, occ, surfY, dirtY, graniteY, basaltY, magmaY, roofY, AMB, worldSeed, surfBase, underD, shallowD, lapse, BW, BH, NB, blockP, blockV, ents, bgm, flyers, ghostBlocks, ghostMolds, awake, hot, hotLvl, tick, tickStamp, machines, molds, nets, pcells, powerDirty, beltL, beltR, tubeLists, brokenMachines, ghostMachines, ghostBlocked, EV, bot, bag, bagTotal, player, seen, ledger, stats
 
-### src/sim/fog.js (46 lines)
+### src/sim/fog.js (51 lines)
 Exploration only: never changes grains or the random stream.
 - functions: fogAlloc, fogMark, fogSeen, fogInit, fogLook, fogRevealAround, fogRevealAll
-- variables: FOG, FOG_SENSE, fog, FW, FH
+- variables: FOG, FOG_SENSE, FOG_SENSE_FADE, fog, FW, FH
 
 ### src/sim/cells.js (176 lines)
 Cell helpers (setCell, move, enter) and the falling-sand movement of powders, liquids and gases (simMove).
@@ -343,7 +343,7 @@ Drawing (src/render/): browser only. This file: the renderer state R, colour tab
 Propagated coloured light from glowing and burning cells.
 - functions: computeLight
 
-### src/render/world.js (297 lines)
+### src/render/world.js (299 lines)
 Scale colour without changing the smooth-look class.
 - functions: fogColor, drawWorld
 - variables: TUBE_CLASS

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,

docs/systems/fog.md

@@ -7,26 +7,30 @@ surface start seen. Exploration never changes the simulation.
 
 `src/sim/fog.js` keeps a `Uint8Array` at half the grain resolution (`FOG = 2`).
 Values run from 0 (unseen) to 255 (seen) and only increase. `alloc` allocates it with
-the other world arrays. `fogInit` reveals above `surfY` and fades eight grains below it.
+the other world arrays. `fogInit` reveals above `surfY` and fades 16 grains below it.
 
-Every four ticks, 256 rays from the bot's centre reveal up to 48 grains. The last eight
-grains fade out. Solid and powder stop sight after a four-grain fade into their face;
+Every four ticks, 256 rays from the bot's centre reveal up to 48 grains. The last 16
+grains fade out. Solid and powder stop sight after an eight-grain fade into their face;
 air, gas and liquid pass sight. Bars and machine voids do not block it.
 
 Each look also senses the ground around the bot through rock: every fog cell within
-`FOG_SENSE` (20 grains) of the bot is revealed, fully clear out to 16 grains and fading to
-nothing at 20, so the player can see ore and caves next to their tunnel and choose where to dig.
+`FOG_SENSE` (24 grains) of the bot is revealed, fully clear out to 12 grains and fading over
+the outer 12 grains to nothing at 24, so the player can see ore and caves next to their tunnel
+and choose where to dig.
 
 ## Saving
 
 The fog buffer is saved and exported with the other typed arrays, without a save version
 change. Older saves rebuild the surface, reveal a radius of 12 grains around built blocks,
-machine footprints and molds, then look from the bot. Loading and generating also look
+machine footprints and molds, fully clear inside six grains with a six-grain fade to the
+radius edge, then look from the bot. Loading and generating also look
 immediately from the bot.
 
 ## Drawing and setting
 
-Both looks and the thermal lens sample fog bilinearly. Seen grains use the usual drawing;
+Both looks and the thermal lens sample fog bilinearly. Partial values get stable per-grain
+noise of about ±40, clamped to 1–255, to break up stepped edges. Unseen and fully seen
+grains are unchanged. Seen grains use the usual drawing;
 unseen grains use the out-of-world colour and smooth-look buffers, hiding their shapes.
 Partial values dim foreground, background and trees. Bloom sources need at least 128;
 bars, flyers, rain and particles need at least 64. Hover info and the cursor label say