Perform a custom action on a task — the generic escape hatch for tasks that expose workflow-specific actions beyond approve/deny.

For approval tasks, prefer POST /tasks/{task_id}/complete or POST /tasks/{task_id}/dismiss — those endpoints are simpler and do not require discovering the action type.

Use this endpoint only when the task exposes custom actions. Discover the available actions for a task with GET /tasks/{task_id}/actions; each returned action includes an action_type (the value to pass in this request body) and the status transitions it can produce.

transition_to is optional — if the action has exactly one possible target status, it is inferred. Pass it explicitly when an action can transition to more than one status.

Responses:

• 204 No Content — action performed.
• 400 Bad Request — unknown action type or invalid transition.
• 403 Forbidden — caller is not authorized to act on the task.
• 409 Conflict — task is already in the requested status.