Route and coordinator disagreed on landed/complete: the route required
mergeConfirmed + matching mergeTargetBranch, the coordinator accepted bare
column===done/in-review and never checked the branch. Extract canonical
isBranchGroupMemberLanded/isBranchGroupComplete in @fusion/core (stricter
route semantics win — load-bearing for merge-target safety) and consume from
both sides. Tightens promotion gating to fire only when all members are
merge-confirmed onto the group branch.
88b4b0d5b3