Engine wires the ports and exposes ProcessNewVideo, the core use case. Returns
ErrNotImplemented on purpose so the acceptance suite fails RED — implementing it
to make those tests pass is the first build task. Depends only on ports + domain
(dependencies point inward).
The hexagonal interfaces the engine depends on. Keeps the engine provider- and
sink-agnostic: YouTube/Vimeo implement VideoSource, the AI router implements
Summarizer, store/brain implement Sink, ESO implements SecretStore. This is what
makes standalone-vs-homelab a wiring choice (ADR-003).
Pure domain types matching docs/data-model.md: User, Subscription, Video,
Transcript, Summary, plus Provider and TranscriptSource enums. Stdlib-only,
no outward dependencies — the innermost layer. Video carries user_id per the
per-user-isolation decision (no global dedup).
mathias