Check transcript coverage for a channel or playlist

Authenticated source-caption coverage for exactly one channel or playlist. Costs 0 credits. Allows 200 requests per free key per UTC day or 2,000 per paid key, including valid warm snapshots. The allowance is checked before upstream work; exhaustion returns 429 QuotaExceeded with Retry-After until 00:00 UTC. The normal key request rate also applies. A cold first enumeration page consumes the separate normal enumeration allowance and Data API capacity; further contiguous warm pages extend the snapshot without additional cold enumeration. Missing IDs and the create_job cold selection are capped at 500. snapshot_complete is false while source enumeration is truncated; next_offset identifies the next enumeration page. Display metadata is refreshed only when the original listing snapshot changes; repeated warm calls do not rewrite unchanged fields or extend their original 30-day freshness deadline. Indexing preserves newer listing metadata. Required counts.uncaptioned counts known non-indexed videos recorded as no_captions or unavailable; they are excluded from missing and cold selections. An existing searchable index takes precedence. complete is true only for a complete source snapshot with nothing indexable missing, and may be true while counts.uncaptioned is positive. This does not promise captions for every known video.