Record one immutable Stratum enforcement event against this workspace's rules. Idempotent on ``event_id``: a replay returns 200 with ``created: false`` and the item id of the event already stored. Errors: 400 ``invalid_event`` — the event violates the exchange contract. 400 ``deviation_requires_human`` — ``outcome='deviation'`` without ``resolved_by='human'``, ``resolved_by_user_id`` and ``rationale``. 400 ``workspace_mismatch`` — a cited rule source belongs to another workspace.