generate_skeleton / compute_district_mix / derive_layout_mode /
organic_placements / derive_reservations now take a SeedChain instead of a
bare seed: u64. The two ad-hoc wrapping_add pre-mixing hacks are replaced with
real domain separation:
- district-type allocation draws from chain.derive(SeedDomain::Layer4Quarter, 0)
- organic block placement draws from chain.derive(SeedDomain::Block, 0)
DistrictSkeleton.seed now records chain.seed(); test call sites pass
SeedChain::root(N); stale seed-param docs updated.
Re-tuned all_district_types_can_appear: the seed-stream change exposed it as
latently fragile — every type has a clamped weight >= 1 (reachable), but 50
weighted draws can miss a low-weight type (Administrative) depending on the
sequence; the old seed got lucky. Raised the draw count to 500 so it tests
genuine reachability rather than a lucky sequence. Determinism-affecting by
design — this is the RNG-using layer D-224 flagged.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.7
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