Every Atlas rung currently re-derives from the heightmap independently. D-258
inserts one deterministic whole-body layer between the baked inputs and the
ladder, and points every deeper rung at it instead of at the source files.
Two failures forced it. The Global rung was deriving a five-class hue map
while a per-body artefact labelled "clean color hypsometric render (display /
Atlas)" sat unused beside it. And hydrology was not derivable at all: flow is
a global solve, so no per-window derivation could produce a coherent water
system — Region carried no courses and lakes could not fill.
The record also fixes what the reliefmap IS. It is a plurality, not a
classification: each cell names the biome dominating ~38 km, a vote already
counted and discarded. So rung 0.5 un-summarises it rather than upscaling it,
which binds three consequences — biome edges are gradients never lines
(D-243's climate rule extended to biome), descending reveals composition
rather than sharpness, and invented detail must downsample back to the
summary it came from. That last one is the acceptance gate for any sub-biome
algorithm.
Rung 0.5 is a stored derived artefact and therefore a named carve-out from
D-227's derive-don't-store. The boundary is principled: D-227 governs what is
LOCALLY computable, where storage is pure cost. A whole-body flow solve is not
locally computable by construction — that is why it must exist — so storage
here buys correctness, not convenience. Everything below rung 0.5 stays
derive-don't-store.
Record precedes implementation; no code changes here. Complements the same
session's D-255 extent inversion, which governs how a canvas is sized rather
than what it is made of.
Pair session with Jeroen, 2026-07-26.
Co-Authored-By: Claude <noreply@anthropic.com>
jpmschweitzerandClaude
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