diff --git a/docs/DESIGN.md b/docs/DESIGN.md
index f65b817..4fd79ed 100644
--- a/docs/DESIGN.md
+++ b/docs/DESIGN.md
@@ -234,6 +234,10 @@ above, including:
   the bag; Ctrl+click a bag name adds it to the blow mix and Ctrl+right-click to pick-up; the menu
   is one line per material because the first version was too large.
 
+- **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.
+
 ## Ideas not built yet
 
 - **Concrete**, as a stronger wall material from rubble.
diff --git a/docs/PROJECT_MAP.md b/docs/PROJECT_MAP.md
index ac70253..e504ce7 100644
--- a/docs/PROJECT_MAP.md
+++ b/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 (35 lines)
+### src/sim/fog.js (46 lines)
 Exploration only: never changes grains or the random stream.
 - functions: fogAlloc, fogMark, fogSeen, fogInit, fogLook, fogRevealAround, fogRevealAll
-- variables: FOG, fog, FW, FH
+- variables: FOG, FOG_SENSE, 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).
diff --git a/docs/agent-log.md b/docs/agent-log.md
index 1bdecc3..cd5feb7 100644
--- a/docs/agent-log.md
+++ b/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: 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,
+  through rock (full to 16, fading to 20). Claude rewrote Codex's per-grain `Math.hypot` loop to
+  work per fog cell. `fogLook` cost: 0.042 → 0.043 ms (every 4 ticks).
+- `test/t_fog.js`: rock 12 grains away is seen, near the edge partly, 25 away still hidden.
+- `docs/systems/fog.md`, DESIGN.md decision. Also: `.kandown/kandown_work.md` rule to write
+  tasks from chat in our own words (no owner labels, dates or quotes); t16/t19 descriptions
+  rewritten that way; `docs/kandown.md` notes that web-board descriptions were lost.
+- Tests: `run_all.py --browser` all pass (220 `play.py` checks). `t_smooth` half-resolution failed
+  on two runs while the machine was loaded (load 6–10) and passed on the final run; timing
+  `fogLook` showed the change is not the cause. Screenshot `shots/fog-sense.png` checked.
+
 ## 2026-10-24: t19 Vacuum blow all visual (Claude Code, Codex)
 
 - The owner's description was lost in kandown; chosen in chat: bag rows light up and the card
diff --git a/docs/systems/fog.md b/docs/systems/fog.md
index edff906..bb90261 100644
--- a/docs/systems/fog.md
+++ b/docs/systems/fog.md
@@ -13,6 +13,10 @@ Every four ticks, 256 rays from the bot's centre reveal up to 48 grains. The las
 grains fade out. Solid and powder stop sight after a four-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.
+
 ## Saving
 
 The fog buffer is saved and exported with the other typed arrays, without a save version
diff --git a/src/sim/fog.js b/src/sim/fog.js
index 638c4a8..a250b35 100644
--- a/src/sim/fog.js
+++ b/src/sim/fog.js
@@ -1,5 +1,6 @@
 // Exploration only: never changes grains or the random stream.
 const FOG = 2;
+const FOG_SENSE = 20; // Reveal nearby ground through rock, in grains.
 let fog, FW, FH;
 function fogAlloc() { FW = Math.ceil(W / FOG); FH = Math.ceil(H / FOG); fog = new Uint8Array(FW * FH); }
 function fogMark(x, y, v) {
@@ -28,6 +29,16 @@ function fogLook(cx, cy) {
       fogMark(x, y, v);
     }
   }
+  // one fog cell at a time, measured from its centre; full inside FOG_SENSE - 4, fading to the edge
+  const R2 = FOG_SENSE * FOG_SENSE, in2 = (FOG_SENSE - 4) ** 2;
+  const fy0 = Math.max(0, Math.floor((cy - FOG_SENSE) / FOG)), fy1 = Math.min(FH - 1, Math.floor((cy + FOG_SENSE) / FOG));
+  const fx0 = Math.max(0, Math.floor((cx - FOG_SENSE) / FOG)), fx1 = Math.min(FW - 1, Math.floor((cx + FOG_SENSE) / FOG));
+  for (let fy = fy0; fy <= fy1; fy++) for (let fx = fx0; fx <= fx1; fx++) {
+    const dx = (fx + 0.5) * FOG - cx, dy = (fy + 0.5) * FOG - cy, d2 = dx * dx + dy * dy, i = fy * FW + fx;
+    if (d2 >= R2) continue;
+    const v = d2 <= in2 ? 255 : (FOG_SENSE - Math.sqrt(d2)) * 255 / 4;
+    if (v > fog[i]) fog[i] = v;
+  }
 }
 function fogRevealAround(x, y, r) {
   for (let yy = Math.max(0, Math.floor(y - r)); yy <= Math.min(H - 1, y + r); yy++) for (let xx = Math.max(0, Math.floor(x - r)); xx <= Math.min(W - 1, x + r); xx++) if ((xx - x) ** 2 + (yy - y) ** 2 <= r * r) fogMark(xx, yy, 255);
diff --git a/test/t_fog.js b/test/t_fog.js
index 10de206..bfe60a0 100644
--- a/test/t_fog.js
+++ b/test/t_fog.js
@@ -9,6 +9,9 @@ rect(run, 40, 100, 140, 110, run('EMPTY'));
 rect(run, 40, 125, 140, 135, run('EMPTY'));
 run('bot.x = 60; bot.y = 102; fogLook(62.5, 104.5)');
 check('open pocket is visible', run('fogSeen(82, 104) >= 200'));
+check('sense test points are rock', run('mat[117 * W + 62] === STONE && mat[122 * W + 62] === STONE'));
+check('nearby rock is clearly seen through the floor', run('fogSeen(62, 117) >= 200'));
+check('rock near the sense edge is seen', run('fogSeen(62, 122) > 0'));
 check('rock hides separate pocket', run('fogSeen(62, 130) === 0'));
 check('one look has limited range', run('fogSeen(124, 104) === 0'));
 check('fog only increases', run('(()=>{const f = fog.slice(); fogLook(90,104); return f.every((v,i)=>fog[i]>=v)})()'));