Layer 1 backstop — transcribe eligible content that has none.

THE ONLY PATH for reference-only content. Farcaster auto-tokenised pieces never pass through upload/complete, so no upload trigger can reach them; run_pending existed for exactly this and had zero callers until now.

Also the net under the create-content trigger, for a piece whose upload finished after its content row was written, and for any piece marked pending_ai_key whose creator has since connected a key.

BYOK-only, like every AI surface: extract() hard-stops without a connected audio-capable provider and marks the row rather than spending anything. Thumbnail-only historical imports are excluded by is_transcript_candidate — a JPEG has no audio and attempting one would only consume the run's budget.