feat(cache): opportunistic cache sync on metadata read with in-place update

- 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)

tests/services/test_persistent_model_cache.py

@@ -225,3 +225,119 @@ def test_incremental_updates_only_touch_changed_rows(tmp_path: Path, monkeypatch
     assert second['metadata_source'] == 'archive_db'
     assert second['civitai_deleted'] is True
     assert second['civitai']['creator']['username'] == 'builder_v2'
+
+
+# ── update_single_model ───────────────────────────────────────────────
+
+
+def test_update_single_model_insert(tmp_path: Path, monkeypatch):
+    """Insert a brand-new model row via update_single_model."""
+    monkeypatch.setenv('LORA_MANAGER_DISABLE_PERSISTENT_CACHE', '0')
+    db_path = tmp_path / 'cache.sqlite'
+    store = PersistentModelCache(db_path=str(db_path))
+
+    file_path = (tmp_path / 'x.safetensors').as_posix()
+    new_item = {
+        'file_path': file_path,
+        'file_name': 'x',
+        'model_name': 'Model X',
+        'folder': '',
+        'size': 42,
+        'modified': 1.0,
+        'sha256': 'sha-x',
+        'base_model': 'SDXL',
+        'preview_url': '',
+        'preview_nsfw_level': 0,
+        'from_civitai': True,
+        'favorite': True,
+        'notes': 'test note',
+        'usage_tips': '{}',
+        'metadata_source': None,
+        'exclude': False,
+        'db_checked': False,
+        'last_checked_at': 0.0,
+        'tags': ['test', 'new'],
+        'civitai': None,
+        'civitai_deleted': False,
+        'skip_metadata_refresh': False,
+        'license_flags': DEFAULT_LICENSE_FLAGS,
+        'hash_status': 'completed',
+        'hf_url': '',
+    }
+
+    store.update_single_model('dummy', new_item)
+
+    persisted = store.load_cache('dummy')
+    assert persisted is not None
+    items = {item['file_path']: item for item in persisted.raw_data}
+    assert file_path in items
+    assert items[file_path]['model_name'] == 'Model X'
+    assert items[file_path]['favorite'] is True
+    assert sorted(items[file_path]['tags']) == ['new', 'test']
+
+
+def test_update_single_model_update_tags(tmp_path: Path, monkeypatch):
+    """Tags are updated incrementally: old tags removed, new tags added."""
+    monkeypatch.setenv('LORA_MANAGER_DISABLE_PERSISTENT_CACHE', '0')
+    db_path = tmp_path / 'cache.sqlite'
+    store = PersistentModelCache(db_path=str(db_path))
+
+    file_path = (tmp_path / 'y.safetensors').as_posix()
+    base = {
+        'file_path': file_path, 'file_name': 'y', 'model_name': 'Y',
+        'folder': '', 'size': 1, 'modified': 1.0, 'sha256': 'sha-y',
+        'base_model': '', 'preview_url': '', 'preview_nsfw_level': 0,
+        'from_civitai': True, 'favorite': False, 'notes': '', 'usage_tips': '{}',
+        'metadata_source': None, 'exclude': False, 'db_checked': False,
+        'last_checked_at': 0.0, 'civitai': None, 'civitai_deleted': False,
+        'skip_metadata_refresh': False, 'license_flags': DEFAULT_LICENSE_FLAGS,
+        'hash_status': 'completed', 'hf_url': '',
+    }
+
+    # First insert with tags [alpha, beta]
+    store.update_single_model('dummy', {**base, 'tags': ['alpha', 'beta']})
+
+    # Now update: replace with [beta, gamma]
+    old_item = {'file_path': file_path, 'tags': ['alpha', 'beta'], 'sha256': 'sha-y'}
+    new_item = {**base, 'tags': ['beta', 'gamma']}
+    store.update_single_model('dummy', new_item, old_item=old_item)
+
+    persisted = store.load_cache('dummy')
+    assert persisted is not None
+    items = {item['file_path']: item for item in persisted.raw_data}
+    assert sorted(items[file_path]['tags']) == ['beta', 'gamma']
+
+
+def test_update_single_model_update_hash(tmp_path: Path, monkeypatch):
+    """When sha256 changes, the hash_index is updated incrementally."""
+    monkeypatch.setenv('LORA_MANAGER_DISABLE_PERSISTENT_CACHE', '0')
+    db_path = tmp_path / 'cache.sqlite'
+    store = PersistentModelCache(db_path=str(db_path))
+
+    file_path = (tmp_path / 'z.safetensors').as_posix()
+    base = {
+        'file_path': file_path, 'file_name': 'z', 'model_name': 'Z',
+        'folder': '', 'size': 1, 'modified': 1.0, 'base_model': '',
+        'preview_url': '', 'preview_nsfw_level': 0, 'from_civitai': True,
+        'favorite': False, 'notes': '', 'usage_tips': '{}',
+        'metadata_source': None, 'exclude': False, 'db_checked': False,
+        'last_checked_at': 0.0, 'tags': [], 'civitai': None,
+        'civitai_deleted': False, 'skip_metadata_refresh': False,
+        'license_flags': DEFAULT_LICENSE_FLAGS, 'hash_status': 'completed', 'hf_url': '',
+    }
+
+    store.update_single_model('dummy', {**base, 'sha256': 'old-hash'})
+
+    old_item = {'file_path': file_path, 'tags': [], 'sha256': 'old-hash'}
+    new_item = {**base, 'sha256': 'new-hash'}
+    store.update_single_model('dummy', new_item, old_item=old_item)
+
+    persisted = store.load_cache('dummy')
+    assert persisted is not None
+    # old hash should be gone from hash_index
+    old_hash_pairs = [p for p in persisted.hash_rows if p[0] == 'old-hash']
+    assert len(old_hash_pairs) == 0
+    # new hash should be present
+    new_hash_pairs = [p for p in persisted.hash_rows if p[0] == 'new-hash']
+    assert len(new_hash_pairs) == 1
+    assert new_hash_pairs[0][1] == file_path