POST /projects/{projectId}/briefs/{briefId}/actions/{actionKey}

POST /api/v1/projects/{projectId}/briefs/{briefId}/actions/{actionKey} on the Caveman Cloud control plane. Requires the opportunity:write scope. Exposed to autonomous agents as the act action of the caveman_briefs_write tool (write access). Rewrite a brief through the same write path people use (every claim cited, the version you read), move its status, assignee or priority, comment, and run its declared actions: mark done, dismiss, or prove it on recorded traffic (queues a replay whose result reads back as the brief's proof, always inferred). Fix is a person's action from their own session; your agent takes the fix itself by pulling the brief's fix packet and reporting back, which the brief shows as self-reported.