Tyre's re-review found the C1 !Barren guard only covered the Grassland arm — the Wetland arm was an unconditional => true. Since derive_morphology_zone has no temperature gate, a frozen + wet + flat district still yields Wetland material, so the wetland palette would paint copse/bog onto frozen marsh: the exact C1 symptom via the material path. Not a regression (the arm was unchanged) and unreachable by the 2 harness bodies, but the D-246 amendment + the voxel.rs comment already claim the guarantee universally, so the gate must match the claim.
Gate is now: apply = !Barren && class in {Wetland, Forest, Grassland}. Behavior change is limited to frozen/hyper-arid Wetland districts (a temperate marsh is never Barren-dominant; Forest is Barren-free by construction). believability.json unchanged (neither harness body reaches the frozen-wet case). New regression test mosaic_pass_does_not_revegetate_frozen_wetland; D-246 amendment reworded to the unified gate. Full cargo test green; clippy -D warnings clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8
895bb83bad