Use luminance pairs after the existing camera looks fail their colour-pair
minimum. Keep the source colour, exclude clipped pixels from training, and
check held-out luminance and each clipped pixel before accepting the curve.
The darkest supplied D610 sample changes from +2.81 to -0.09 stops at the
median. The other 15 renders are byte-identical. Add synthetic coverage for
source-colour precedence, independent holdout and invalid or clipped input.
Bump LOOK_VERSION to 10 and RENDER_CACHE_VERSION to 67 after checking open PRs.
Engine tests pass. Workspace tests pass with only the known #1457 overlay
test excluded. Formatting, Clippy, HEIC, parity, layers, assets and WASM pass.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
