[moetemp]

This PR adds session start, session running and session watch, so the detached lifecycle the durable executor already supports can be driven from a command line.

A session is a workflow rather than a process, the running set comes from Temporal visibility, the store is shared, and a live tail re-reads. Put together, a session can outlive its client; nothing said so, and nothing on the command line could use it. The commands are thin HTTP clients against any serve in the deployment, because the serves are interchangeable, and they never talk to Temporal.

start hands a prompt over and returns the session id. running reads the executor's own answer, so it survives a restart of whichever process answers. watch follows a session from a machine that has never seen it and exits when the turn stops. The turn now publishes its own durable ending, session.next.turn.ended, because a step ending is not a turn ending (a steer or a queued prompt continues the same turn) and a follower in another process has only the replayable stream to read. A turn the user stopped or a provider error ended has no ordinary ending, so a slow poll of the running set is the backstop.

scripts/detached-session-check.sh proves it against real processes: a Temporal dev server, one standalone worker, two serve processes and one shared store. Serve A starts a turn and is killed with a tool still running; the turn finishes on the worker; serve B, which never saw the session, reports it running and replays the transcript; then start, running and watch work from a cold client. The assertions were mutation-checked: giving serve B its own store makes exactly the cross-process ones fail.

The schedule command, the container check, the worktree quarantine and the turn budget, which used to ride in this PR, are their own PRs in the stack now.

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