Hoshe finding 1: derive_all_districts passed a permanently-empty
region_cache, so every survey cell paid four on-the-fly baseline
derivations — and derive_district_profile's docstring (build the cache
before calling in a loop) was contradicted by its sole production
caller. The cache is now pre-built on the TRUE region keys the shared
core looks up (survey-cell centre metres -> containing district ->
region ±1 ring, BTreeSet-deduped), restoring the per-body build-once
cost model. Cache-hit == cache-miss byte-identity holds by D-227 purity
(build_region_profile and the miss branch share the same expressions) —
verified by the believability harness passing against the UNCHANGED
golden. Finding 2: the cascade.rs call-site comment and the stale
module header now state the pre-build truthfully.
Found in passing, filed as T-1186 (pre-existing, out of scope here):
region_centre_latitude_deg is pole-anchored while the derive core keys
equator-anchored signed regions — northern-hemisphere baselines clamp
to +90.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
jpmschweitzerandClaude Fable 5
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