ensureCommitTaskMetadata (was ensureTaskTrailersOnHead) now also prefixes the
commit subject with `<taskId>: ` when includeTaskIdInCommit is on, in addition
to ensuring the Fusion-Task-Id / lineage trailers — so the landed commit both
starts with the task id and carries the board-association trailers even if the
AI agent omits them. Single idempotent amend.
Test: asserts the landed subject matches /^FN-1: / when the agent committed
without a prefix.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
7f536eb619