Replace or clear a revision's flow graph

Validation result for a submitted CompiledWorkflowGraph payload.

Full revision response — the compile-poll target (WF-08).

Clients poll GET /workflows/revisions/{id} and read compilation_status

• compilation_errors + compiled_graph to determine whether an async compile job is done. compilation_task_id is the Celery task handle the conductor uses to cancel an in-flight compile.