Make the document (PDF) exclusivity validation — previously web-only — also apply when scheduling/publishing via the public API and MCP, so a misconfigured post can't slip through these entry points.
- ContentTypeCompatibleWithMedia: stored-media fallback for partial updates + a stored-state assertStoredPostCompatible(Post)
- MCP PublishPostTool: assert stored-state compatibility before publish (the media-side mirror of assertStoredPostPublishable)
- API UpdatePostRequest: validate each platform's effective content_type against effective media on schedule/publish (covers publishing without resubmitting content_type)
- MCP UpdatePostTool: apply the rule on schedule with stored-media fallback
- Tests: API + MCP happy + rejection paths, plus rule fallback/precedence units
14e44538a7