Pre-gateway PMs/Board sent formal notifications (require ack); gateway
had say/dm only. Now PMs and Board can issue ack-required notifications
via NotificationService through the standard envelope path.
ContentActions.commit was stripping user-supplied prefixes but never
re-adding the canonical one. Dev prompt promised auto-prefix; code
delivered nothing. Now every gateway commit lands with [task-id-short].
Format choice: simple [task_id[:8]] (8-char), matching the dev prompt
("Auto-prefixes [task-id]") and CLAUDE.md's documented commit format.
The legacy templates/git/commit.py uses the richer
[root_short:task_short] for the commit_for_task API path with full
traceability metadata; the gateway commit path is intentionally simpler
and stays aligned with the prompt-level promise.