The nightly cold-on-latest run promotes canonical->LATEST, so every subsequent
nightly (until a new version ships) finds canonical==latest==version-under-test
-> base==head -> same-version no-op. This is the common path, not a rare edge.
M2 now proves the fix on that nightly scenario (canonical already==latest ->
step back to previous published).
Operator 2026-06-17. Closes the prevb resolver gap: when the last-green
warm-canonical base version equals the PR head version, step back to the
newest published version strictly older than head (design A) instead of a
same-version no-op or a skip. Design B (canonical history for a green-verified
older base) saved to IDEAS. Auto-runs after regall (watchdog advances + switches
to opus).
