Read a story job by id, including its artifacts.

Poll this to follow status + progress. Terminal states: READY, PARTIAL, FAILED, CANCELED. A RESERVED job with progress.stage: provider_backoff is nonterminal: Sleeper Hit has retained its credits/checkpoint and scheduled the retry, so clients should keep polling rather than implement provider backoff. A RUNNING job with runStale: true lost its worker mid-run: POST /story-jobs/{jobId}/resume sends it on from its last checkpoint at no new cost (Sleeper Hit also does when its workers restart). Each artifact carries its manifest URLs once status: READY.