Starts a run of a published flow whose first node is a webhook, scheduled, or manual
trigger. A draft flow is rejected with 422 — use actions/test-run to run one.

No Idempotency-Key is required. This is a state transition, not a resource creation.

The response is a snapshot taken at dispatch, so status is always pending and the
timing fields are not yet populated. Read the run back through
GET /cloudflow/v1/flows/{flowId}/runs/{runId} to follow its progress.

A flow holds a concurrency lock while it runs, so triggering one that is already running
returns 409 with the active run embedded in the problem body — no second lookup needed.