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