The retarget-main-to-staging workflow tries to PATCH base=staging on
every bot-authored PR opened against main. Auto-promote staging→main
PRs have head=staging, base=main — retargeting them sets head AND
base to staging, which GitHub rejects with HTTP 422 "no new commits
between base 'staging' and head 'staging'".
This started surfacing on PR #2588 (2026-05-03 14:30) once #2586
switched the auto-promote workflow to an App token. Before #2586
the auto-promote PR was authored by github-actions[bot], which the
retarget filter happened to skip; now it's molecule-ai[bot], which
passes the bot filter and triggers the broken retarget attempt.
Add a head-ref != 'staging' guard so auto-promote PRs short-circuit
before the PATCH. The existing 422 "duplicate base" detector is
left alone — it covers a different operational case.
2b3f44c3c8