Level lakes at the end of world generation, keeping their water (t96)

Volume-preserving levelling pass for water bodies of 50+ cells; the dock foundation is placed
first so it cannot erase levelled water. Seed hashes re-baselined (water and air only).
Started by Codex, finished and reviewed by Claude after Codex hit its usage limit.

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

docs/DESIGN.md

@@ -590,12 +590,15 @@ above, including:
   ordinary repose rules take over. Keep stamped moves, barriers, burning-bed protection and
   worker independence. The existing worldgen POWDER_FAN switch disables new face releases.
 
-- **New-world lakes wake immediately; keep the seed layout (t96, 2026-10-29).** Keep the
-  recorded worldgen settling speeds and material/temperature output. Wake water after the
-  final startup reset so unfinished lakes level without drilling. Retain tree candidates and
-  their random draws, then omit whole trees whose bases are wet or on an open bank connected
-  to water at base height after settling. This keeps trees out of the lake as it spreads.
-  Existing load wake scheduling and later snowmelt/flooding rules stay as they are.
+- **Level lakes during world generation (t96, 2026-10-29).** The owner wants new worlds
+  to start with flat lakes instead of waiting 80–125 seconds for them to flow level. Changed
+  generated worlds are accepted: seeds no longer reproduce the old water layout. After the
+  existing settling loop, level four-connected water bodies of at least 50 grains, preserving
+  their exact volume. Fill reachable air/water from the bottom upward, respecting solid/powder
+  walls and dry rims; place a partial top row from the middle outward. Establish the dock's
+  existing foundation first so it cannot erase newly levelled water. Keep the pinned settling
+  values, startup water wakes, and round-1 wet/water-connected-bank tree filtering. Existing
+  load wakes and later snowmelt/flooding rules stay as they are.
 
 ## Ideas not built yet
 

docs/PROJECT_MAP.md

@@ -322,9 +322,9 @@ Bars and other loose objects (ents), and the bag: adding, taking, costs and refu
 - functions: entSolidCell, entSupportCount, entFreeAt, entMark, spawnBar, removeEnt, entScrewAt, entScrewFree, entScrewMove, entScrewLane, entScrewEdge, entScrewEnter, entScrewTick, entDiagonalScrewTick, entBeltScrewEnter, entSlopeBeltTick, entTick, entsInCircle, bagAdd, bagTake, giveOrDrop, refundAt, canAfford, payCost, fmtMoney, costText, needText
 - variables: BAR_W, BAR_H, entCurM, droppedLast
 
-### src/sim/tools.js (65 lines)
+### src/sim/tools.js (30 lines)
 Tool helpers: reach, brushes, and plain digging.
-- functions: setBuildRange, inBuildRange, inReach, forBrush, drillReach, inDrillReach, toolDig
+- functions: setBuildRange, inBuildRange, inReach, forBrush, drillReach, inDrillReach
 - variables: BUILD_MAX, buildBox
 
 ### src/sim/drill.js (183 lines)
@@ -378,12 +378,12 @@ The same chunk schedule runs inline or in workers. Workers only own a pass at a
 simTick: one simulation step, in order.
 - functions: simTick
 
-### src/sim/worldgen-helpers.js (61 lines)
+### src/sim/worldgen-helpers.js (131 lines)
 World generation helpers: noise and removal of tiny hard rock specks.
-- functions: makeNoise, fbm, clearHardSpecks
+- functions: makeNoise, fbm, clearHardSpecks, levelWorldWater
 - variables: SPECK_MIN
 
-### src/sim/worldgen.js (303 lines)
+### src/sim/worldgen.js (305 lines)
 World generation: staged terrain, ore, caves and placement, with synchronous and async entry points.
 - functions: generateWorld, generateWorldAsync
 
@@ -397,9 +397,9 @@ Saving and loading a world (serializeWorld / deserializeWorld) and old-save migr
 - functions: serializeWorld, deserializeWorld, startLoadWake, wakeLoadArea, wakeLoadNearBot, loadWakeTick
 - variables: SAVE_VERSION, TOFF
 
-### src/render/setup.js (190 lines)
+### src/render/setup.js (188 lines)
 Drawing (src/render/): browser only. This file: the renderer state R, colour tables (glow, thermal palettes, pipes, trees, sky), canvas setup and the camera.
-- functions: glowIndex, thermIdx, pipeCellColor, pipeBodyCell, thinPipeColor, beltLike, buildSky, initRender, resizeRender, viewCells, updateCamera, snapCamera, screenToWorld, worldToScreenPx, renderMonoFont
+- functions: glowIndex, thermIdx, pipeCellColor, pipeBodyCell, thinPipeColor, buildSky, initRender, resizeRender, viewCells, updateCamera, snapCamera, screenToWorld, worldToScreenPx, renderMonoFont
 - variables: R, GLOW_W, GLOW_R, GLOW_G, GLOW_B, THERM, PC, TREE_R, TREE_G, TREE_B, BG, SKY_R, SKY_G, SKY_B
 
 ### src/render/slope-belts.js (167 lines)
@@ -664,7 +664,9 @@ The frame loop and boot.
 - `test/t_gpu_light.py`: The former CPU light behavioural checks, now read from the actual GPU light grid.
 - `test/t_import_save.js`: Import must preserve the running world before reading or replacing it.
 - `test/t_joins.js`: The oracle states the geometric rule independently of the precomputed neighbour tables.
-- `test/t_lakes.js`: Generated lakes wake without a tool, settle on their own, and have dry tree bases.
+- `test/t_lakes.py`: Pixel startup and fresh/reloaded flat lakes after 600 ticks; shots/t96-level.png.
+- `test/t_lakes.js`: Generated lakes start flat, conserve water, and have dry tree bases.
+- `test/t_lakes.py`: t96: flat generated lakes, fresh and reloaded, in the real pixel frame loop.
 - `test/t_load.js`: Reload wakes nearby areas first, without losing distant water, fire or saved state.
 - `test/t_molds.js`: Molds and furnaces stay usable: ingots drop below and keep their stubs, plugs over molds are cleared, spoiled castings can be knocked out, grains never drop through a grate by teleporting, and slag lets the fire breathe.
 - `test/t_nozzle.js`: Blowing aims within the nozzle's reach, with room for the brush and settling.

docs/TESTING.md

@@ -76,9 +76,14 @@ The conveyor fixture uses a wider feed pile, the screen fixture warms longer, an
 checks waking within eight ticks separately from the probabilistic consumption of fuel.
 
 `test/t_lakes.js` pins SHA-256 over raw `mat` followed by Float32 `temp` bytes for seeds
-7, 42 and 424242 at 2048x1024. These hashes predate t96 and must not be re-baselined for a
-wake/background-tree change. It also checks generated tree bases, startup wakes, and the
-seed-7 lake leveling within two grains after 6,000 undisturbed ticks, fresh and reloaded.
+7, 42 and 424242 at 2048x1024. t96 round 2 re-baselines only for the lake-levelling pass;
+`t_corner_seal.js` also pins three smaller worlds with the same intentional change. The lake
+suite checks all five seeds (also 2 and 1): surface pools wider than 20 grains start within
+one grain of level and stay so after 600 ticks, exact WATER count from the pre-pass 0.99
+progress callback, dry tree bases and startup wakes. Small fixtures cover solid/powder rims,
+volume, centered partial rows, the 50-grain cutoff and diagonal separation.
+`python3 test/t_lakes.py` checks pixel startup and fresh/reloaded lakes after 600 ticks with
+two browser helpers and no page errors; `shots/t96-level.png` shows the untouched new lake.
 
 `test/t_bot_rescue.js` covers deep basalt burial, nearest/upward and diagonal nudges,
 unexplored-pocket rejection, newest open trail points, ring wrap/load reset, bounded searches,

docs/agent-log.md

@@ -4,6 +4,26 @@ 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.
 
+## 2026-10-29: t96 round 2 — level lakes during generation (Codex)
+
+- Level 50+ grain water bodies with typed-array flood fills, exact volume and centered partial
+  rows; keep settling switches, startup wakes and tree rules. Establish the existing dock
+  foundation first (otherwise seed 42 loses 39 grains). Recorded the owner's changed-seed decision.
+- Files: src/sim/worldgen{,-helpers}.js, test/t_lakes.{js,py}, test/t_corner_seal.js,
+  docs/{DESIGN,TESTING,PROJECT_MAP}.md, tasks/t96* and this log.
+- Eight regressions failed first; all 40 headless suites pass (59 lake checks). Six world hashes
+  re-baselined only for WATER/EMPTY redistribution; bypassing the pass restores all six originals.
+  Pixel browser fresh/reload seed 7 at 600 ticks passes with two helpers and no page errors.
+  Inspected shots/t96-level.png: flat lake, centered one-grain top row, dry bank trees, dock at right.
+- Paired generation medians before→after (ms), seeds 7/42/424242: 871.09→903.88,
+  921.47→981.33, 1067.50→1119.16. Pass medians 13.67/22.17/15.27 ms; max 24.05
+  measured / 41.22 cold. Evidence: /tmp/t96-round2-{red,headless-final,browser,paired-times}.log.
+  Review pending; no full browser suite, no commit.
+- Claude finished the run after Codex hit its usage limit: registered test/t_lakes.py in run_all.py's
+  browser list; full `run_all.py --browser` passed except the known flaky t_smooth.py (t99), which
+  passed 3/3 reruns. Found that 4 of 12 seeds' levelled lakes now reach the trade dock's wall
+  (none enter it); cause is the lake lip using the highest rim point (see t96).
+
 ## 2026-10-29: t69 hot-load warning, visible damage and build-over repair (Codex)
 
 - Added persistent scorched/fractured screw overlays in both looks, 900°C load warnings,