Dry-run the FULL save-time authoring guard set against a Composition body WITHOUT persisting it and without a project. Runs the same pure, DB-free guards saveComposition enforces — wire shape, primitive membership (unknown_primitive / custom_missing_sourcecode), required-param shape (invalid_primitive_params), clip↔track family (clip_source_track_mismatch), and reframe coverage (reframe_coverage_gap) — and returns ONE shape, `200 { valid, errors[] }`, for BOTH wire-shape and deep-invariant…