faad4b57 shipped the field, shader scale, and plumbing but the
scripted edit inserting the sdr_white_level_scale() refresh in the
scratch-rebuild arm matched nothing and silently no-op'd (no assert) —
sdr_white_scale stayed at its 1.0 init, i.e. 80 nits, i.e. exactly the
old dark cursor. Now queried on every scratch rebuild, with an info
log of queried/applied so an HDR session shows what it uses.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>