- Add PersistentModelCache.update_single_model() for lightweight targeted
SQL update (single row + incremental tag/hash deltas, no full table scan)
- Add ModelScanner.sync_cache_from_metadata() with compare-first logic:
skips entirely when cache is already in sync; when stale, updates the
entry in-place (O(1) instead of O(n) remove+append), incrementally
adjusts tag counts/hash index/version index, and resorts only when
sort-relevant fields changed
- Wire sync_cache_from_metadata() into BaseModelService.get_model_metadata()
via fire-and-forget asyncio.create_task — disk I/O is already paid for
- Include identity re-validation guard against concurrent cache replacement
- Add 16 tests covering _cache_entries_differ, sync_cache_from_metadata
(no-change, in-place, fallback, conditional resort), and
update_single_model (insert, tag delta, hash delta)