Read an agent's editable workflow draft and bounded published-version summary

The target agent authorizes the tenant boundary. This is a pure reconciliation read for PATCH/publish clients: it returns the current editable draft and revision, in-memory validation, a safe canvas-only layout, current published-version metadata, and a stable newest-first bounded version page. No provider or AI call, compilation write, repair, lazy creation, audit event, or other mutation occurs. An existing agent without a workflow draft returns 200 with workflow_state=not_created, workflow=null, published=null, and an empty versions page; only a missing or inaccessible target agent is a 404, and an agent in another workspace answers exactly as one that never existed.