Retrieval now reads <dataDir>/cache/decks/<courseId>/<deckId>/text.json and
<dataDir>/cache/transcripts/<courseId>/<lessonId>.json (skipped when the lesson
has a transcript file). DraftSink returns { location?, branch?, commit? }, so
the studio's createDraftWriter(ctx) needs no adapter; generateDraft computes
paths itself and reports the draft branch.
Co-Authored-By: Claude Opus 5.5 <[email protected]>