Update Outline

Low-level direct replacement of the plan. Caller sends the full plan dict; this endpoint does not merge or diff — it replaces.

Prefer refine_outline(apply=true) for conversational edits: it builds the new plan from the running chat and commits atomically. Reach for update_outline only when you already have a fully-formed plan dict (e.g. programmatic transforms, reapplying a saved plan).

Valid after planning has produced a plan, including post-write and cancelled stories. Written chapter rows remain frozen unless an outline-review client explicitly sets allow_written_outline_edits.