domain glossary, context map, ADRs (library-as-source, playout, event queue)

crates/docs/adr/0001-library-as-single-source-of-truth.md

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+# ADR-0001: Library as single source of truth for media
+
+## Status
+
+Accepted
+
+## Context
+
+The system originally had two representations of media: MediaItem (fetched live from providers at schedule-generation time) and LibraryItem (cached in the local database for browsing). The schedule engine bypassed the library entirely and queried providers directly, creating a tight coupling to provider availability and duplicating the concept of "a piece of media."
+
+## Decision
+
+The local library is the single source of truth for all media in the system. Providers (Jellyfin, Plex, local files, YouTube, etc.) are sync sources only — they feed items into the library, but are never queried at runtime by the schedule engine.
+
+One unified type — MediaItem — lives in the library. The schedule engine queries the library, not providers.
+
+## Consequences
+
+- Schedule generation works even when a provider is offline.
+- No more two-type split (MediaItem vs LibraryItem) — one concept, one type.
+- Provider adapters become sync-only: their job is to discover items and upsert them into the library.
+- Stream URL resolution still needs the provider at playback time (the library stores metadata, not video files). This is the one runtime provider dependency.
+- Filters (genres, decade, content type, etc.) operate on library data, not provider APIs.