Read the compact Main Edit, exact time values, and named runtime capability diagnostics.

validation.export_readiness reports whether an mp4 export of this timeline would pass the export planner's plan-level gates ({exportable, reason?, detail?, work_units?, work_unit_budget, coverage: "plan"}): source availability and authorization, export capability audit, and the composited work budget — the same ladder the export lane enforces, priced with the same hydrated media metadata, so valid alone is never mistaken for "exportable". Render-time fidelity refusals (artwork a page cannot render faithfully) are only discoverable by rendering; they decline at export with the offending entity named.