fix(cache): prevent corrupted cache rows from breaking model listings (#730)

Cache corruption (NULL model_name/file_name from legacy DB rows or partial
writes) caused format_response to raise KeyError/AttributeError, failing the
entire /loras/list request and showing no models in the UI.

Fix across three layers:
- format_response (lora/checkpoint/embedding): replace direct dict[] access
  with .get() fallbacks; return None for entries missing file_path
- handlers: filter None entries from list/excluded/fetch/duplicate/conflict
  endpoints instead of letting them crash or appear as null in responses
- model_scanner: always use validate_batch repaired copies (previously
  discarded when no invalid entries, leaving None values in raw_data)
- persistent_model_cache: add or-empty-string guards on read and write for
  nullable TEXT columns (model_name, file_name, folder, base_model, etc.)

tests/routes/test_base_model_routes_smoke.py

@@ -201,6 +201,45 @@ def test_list_models_returns_formatted_items(mock_service, mock_scanner):
     asyncio.run(scenario())
 
 
+def test_list_models_filters_out_corrupted_entries(mock_service, mock_scanner):
+    """Corrupted cache entries (format_response returns None) must not appear
+    in the response items nor cause a 500. See issue #730.
+    """
+    mock_service.paginated_items = [
+        {"file_path": "/tmp/good.safetensors", "name": "Good"},
+        {"file_path": None, "name": "Corrupted"},  # triggers None from format_response
+        {"file_path": "/tmp/also_good.safetensors", "name": "AlsoGood"},
+    ]
+
+    # Override format_response to return None for corrupted entries
+    original_format = mock_service.format_response
+
+    async def conditional_format(item):
+        if item.get("file_path") is None:
+            return None
+        return await original_format(item)
+
+    mock_service.format_response = conditional_format
+
+    async def scenario():
+        client = await create_test_client(mock_service)
+        try:
+            response = await client.get("/api/lm/test-models/list")
+            payload = await response.json()
+
+            assert response.status == 200
+            # Only the 2 non-corrupted entries should appear
+            assert len(payload["items"]) == 2
+            assert payload["items"][0]["name"] == "Good"
+            assert payload["items"][1]["name"] == "AlsoGood"
+            # None should never appear in the items list
+            assert None not in payload["items"]
+        finally:
+            await client.close()
+
+    asyncio.run(scenario())
+
+
 def test_model_types_endpoint_returns_counts(mock_service, mock_scanner):
     mock_service.model_types = [
         {"type": "LoRa", "count": 3},