The rewrite (D-049) starts from a clean slate; this commit is the reference
implementation of the graduated design.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
SeaLevelModel: "flat" (one scalar, SeaLevelValue) or "field" (the
legacy latitude Lerp 0.26..0.15). Only GetSeaLevel's body changes —
all nine call sites (crater carve target, both flood fills, biome
split, beach band, Capitol window, town filters, A* zero-point)
inherit the model automatically; no consumer re-tuning. Default:
flat 0.15, pinned in ServerConfig.json.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>