A read-only deeper-dive over a video's already-stored transcript (ADR-021).
Safe by construction: the Service has no VideoSource and no caption-fetch
dependency — only a Completer factory over the existing LiteLLM gateway — so it
cannot reach YouTube or the rate gate. Reuses the summarizer's truncation
discipline (TAPIR_MAX_TRANSCRIPT_CHARS), reporting the cut so the UI can be
honest about a bounded transcript. Model defaults to the summary's model and is
switchable among an offered, local-first list; an un-offered alias is forced
back to the default so chat can never call the gateway with an arbitrary model.
Ephemeral: history is carried per-request, nothing persisted.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
