Code review (Tier 2) found two P1s: (1) the early no-op fast-path persisted
mergeConfirmed/mergeTargetBranch without mergeTargetSource, so a shared-group
member landing via it could never satisfy the strict completion predicate —
promotion permanently blocked; thread mergeTarget.source through like the
standard landing sites. (2) createGroupPrCallback's findPrForBranch used
state:'all' and could reuse a closed/merged PR from a prior group, persisting
a terminal prState onto a fresh promotion; create path now matches open PRs
only.
bde7bdf766