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Vance Ingalls
4101cb721a
## Summary Add four midpoint (`p=0.5`) regression invariants applied via a `describe` loop over `ALL_SHADERS`, so every existing and future shader transition automatically gets coverage at the most viewer-visible point in the animation. ## Why `Chunk 9G` of `plans/hdr-followups.md`. Existing smoke tests cover only the endpoints (`p=0 ≈ from`, `p=1 ≈ to`), which miss a class of regressions that surface specifically at the midpoint and let shaders silently rot in CI: - A shader becomes a no-op (returns input as-is) - A shader prematurely completes (returns target at midpoint) - A shader doesn't write to the output buffer at all - A shader loses determinism (`Math.random` / `Date.now` / leaked state) ## What changed `packages/engine/src/utils/shaderTransitions.test.ts`: a single `describe` loop over `ALL_SHADERS` that asserts at `p=0.5`: 1. `output ≠ from` — catches no-ops 2. `output ≠ to` — catches premature completion 3. `output` is non-zero — catches blank output 4. `output` is deterministic — catches accidental non-determinism Uses two distinct uniform input colors (40000/30000/20000 vs 10000/10000/10000) so equality checks have distinct byte patterns to compare against. Even shaders that warp UVs (which would be no-ops on uniform input alone) produce `mix16(from, to, 0.5)` at every pixel, distinct from both inputs. ## Test plan - [x] 60 new tests (4 invariants × 15 shaders), all passing. - [x] Any new transition added to the registry automatically picks up the same coverage. ## Stack Chunk 9G of `plans/hdr-followups.md`. Test-only change, independent of all other chunks.