Review P3: when runtime sigmas were present but malformed/empty while a
valid SIGMAS input was wired, behavior fell back to the wired anchor but
the coverage log still read the malformed runtime object and could
report "first 0 of 0 steps". Bind cov to whichever schedule the anchor
actually came from, and extend the fallback to a zero-start runtime
schedule (unusable) instead of going inert while a wired schedule is
available. Tooltip now states the wired input's runtime-fallback role.
Adds wiring tests for the denoise-mask hook: runtime-anchor coverage,
malformed/zero-start runtime fallback to wired, and warn-once inertness.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
