Fire a schedule-triggered workflow immediately, outside its regular schedule.

Restricted to the schedule trigger type: batch/webhook/etc. triggers have their own dedicated entry points (batch_jobs, the public webhook URL) with trigger-specific guardrails this endpoint doesn't replicate. Requires the workflow to be active, same gate the scheduler itself applies in internal_process_due_schedules.

Send an Idempotency-Key header to dedupe retries (a double-click, or a client retry after a timed-out request): a repeat with the same key returns the first call's result instead of firing a second AI task. Without the header, every call fires a new run.