Stop Precompute Build

Stop a running build, wherever it is running.

The break glass for a build that is alive but wedged: the lease it renews keeps it from expiring on its own, so an operator has to be able to say so. Releases the build lock, marks the job stopped, and broadcasts a cancel to every pod.

Nothing being served changes. A build only alters what is published in its final phase, so one stopped before that has published nothing, and whatever it staged stays in Redis for POST /activate to take live if that turns out to be wanted.

There is no restart endpoint: restarting is this call followed by POST /build, which is a new job with its own record either way.

Returns the stopped job in the same shape GET /build/{job_id} serves, with what the stop itself did alongside it.