Why: repeated task-sync calls changed HEAD and invalidated CI even when main had not advanced.
Evidence: SELF red-green regression and 58 task lifecycle tests recorded through make evidence in the task card.
Impact: sync still fetches and validates components, creates records only for an actual merge, and reports the complete final source SHA.
Refs: U1; policy/merge-queue.md; .task/feature-merge-queue-policy-draft.md