- app/services/retriever.py: hybrid BM25 + semantic Retriever with BM25-only fallback when llm=None
- app/services/synthesizer.py: LLM answer synthesis with citation assembly over retrieved chunks
- app/api/chat.py: POST /api/chat endpoint with 402 gate when PAGEPIPER_OLLAMA_URL is unset
- tests/test_synthesizer.py: 3 TDD unit tests (mocked LLM, context building, system prompt)
- tests/test_chat_api.py: 2 integration tests (402 without Ollama, 200 with mocked retriever+LLM)
Implements GET/DELETE /api/library, POST /api/library/{id}/reingest,
POST /api/library/scan, and GET /api/library/{id}/status. Adds FastAPI
app factory with lifespan migrations, BM25 singleton wiring, get_db
dependency, ingest task registry with cf-orch/BackgroundTasks fallback,
and placeholder search/chat routers. All 5 new tests pass (14 total).
