* feat(retain): delta retain — skip LLM re-extraction for unchanged chunks on upsert
When upserting a document (same document_id), instead of deleting all
facts and re-extracting from scratch, compare chunk content hashes
and only process changed/new chunks. Unchanged chunks keep their
existing facts, entities, and links.
- Add content_hash column to chunks table (migration b3c4d5e6f7a8)
- Add chunk delta comparison functions in chunk_storage.py
- Add delta_mode to fact_storage.handle_document_tracking (skip full delete)
- Add update_memory_units_tags for propagating tag changes to existing facts
- Refactor orchestrator into _try_delta_retain and _full_retain paths
- Automatic fallback to full retain for pre-migration data or all-changed scenarios
- Fix ty type error in metrics.py (resource module import on Windows)
- 16 new tests covering entities, links, tags, metadata, edge cases
* refactor(retain): deduplicate delta and full retain paths
Extract shared _insert_facts_and_links() and _extract_and_embed()
functions used by both the full retain and delta retain paths.
Remove delta_mode flag from handle_document_tracking — delta path
uses dedicated upsert_document_metadata() instead.
* chore: regenerate clients, openapi spec, and lockfile
* chore: regenerate docs skill
fd88c0efa5