Lakes fill only to their lower rim and keep clear of spawn and the dock (t96)

The lake lip was Math.min(surfY), the highest ground (y grows downward), so water was poured
above the lower rim and, once levelled, ran up to the trade dock on 4 of 12 seeds. The lip is
now the lower rim edge minus one, and each lake stays 80 grains from spawn. Seed hashes and
the shallow-ore hash re-baselined (changes only under lake basins); golden fixtures also
freeze surfY/dirtY/AMB from the previous generator.

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

docs/DESIGN.md

@@ -599,6 +599,14 @@ above, including:
   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.
+- **Lakes fill only to their lower rim and keep clear of spawn (t96 round 3, 2026-10-29).**
+  The generator took the basin's `lip` as `Math.min(surfY)`, the highest ground (y grows
+  downward), so water was poured above the lower rim and ran out toward low ground; once
+  levelled it reached the trade dock on 4 of 12 seeds. The owner chose option 2: the lip is
+  now the lower of the two rim edges, minus one, so a lake is filled to just under that rim,
+  and each lake's half-width is capped so its edge stays 80 grains from spawn (and the dock).
+  Lakes are smaller and lower: about 180-250 grains wide instead of 250-330, 5-15 grains
+  lower. The random draws keep their order.
 
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