Request cancellation of a run

Asks a pending, running or paused run to stop. Takes no request body.

The answer is always 200 — read the body to learn what happened:

• {"status":"cancelling","cancelled":true} — cancellation was REQUESTED, not completed. A running step is executing inside a worker process, so the request is a flag the executor picks up; the run unwinds and settles as cancelled shortly after. Poll GET /api/runs/{id} until status is terminal. (A pending run is settled immediately even though the response still says cancelling.)
• {"status":"cancelled","cancelled":true} — a paused run, which has no executor to unwind, was settled synchronously.
• {"status":"<settled status>","cancelled":false} — the run was ALREADY terminal; nothing was done and the reported status is the one it already had. This is not an error, so do not retry.

Cancellation is signalled through Redis. If Redis is not configured the call is refused with 503.