fix: mutable-default in VectorStoreRegistry, ruff format, endpoint test

- Root-cause the shard failures on the previous commit: `__init__`'s
  `vector_stores: list = []` default was a shared mutable, so every
  `VectorStoreRegistry()` without an explicit list appended to the same
  underlying list — the four new tests leaked state into one another
  and passed locally only because they were the only registrants.
  Switch the default to `None` and materialize a per-instance list.
- Apply `ruff format` to vector_store_registry.py (fixes `lint` job).
- Add an endpoint-level regression test to raise codecov/patch:
  `test_list_vector_stores_returns_config_sourced_and_leaves_registry_intact`
  exercises the DB-empty + config-loaded branch of `list_vector_stores`
  and asserts the registry is NOT mutated after the call.

litellm/vector_stores/vector_store_registry.py

@@ -94,8 +94,12 @@ class VectorStoreIndexRegistry:
 
 
 class VectorStoreRegistry:
-    def __init__(self, vector_stores: list[LiteLLM_ManagedVectorStore] = []):
-        self.vector_stores: list[LiteLLM_ManagedVectorStore] = vector_stores
+    def __init__(self, vector_stores: list[LiteLLM_ManagedVectorStore] | None = None):
+        # Never bind a mutable default: the previous `= []` default caused every
+        # VectorStoreRegistry() with no argument to share the same list, so a
+        # mutation in one place (test, request handler, etc.) leaked into every
+        # other caller.
+        self.vector_stores: list[LiteLLM_ManagedVectorStore] = list(vector_stores) if vector_stores is not None else []
         self.vector_store_ids_to_vector_store_map: dict[str, LiteLLM_ManagedVectorStore] = {}
         # IDs of vector stores that were loaded from config.yaml / kustomization.
         # These have no DB row, so reconciliation code paths that treat "in memory
@@ -400,8 +404,7 @@ class VectorStoreRegistry:
         list-endpoint reconciliation on the very next reload.
         """
         new_config_ids: set[str] = {
-            (cfg.get("litellm_params") or {}).get("vector_store_id")
-            for cfg in vector_stores_config
+            (cfg.get("litellm_params") or {}).get("vector_store_id") for cfg in vector_stores_config
         }
         new_config_ids.discard(None)  # ids missing here will re-raise below with a clearer error
 

tests/test_litellm/proxy/vector_store_endpoints/test_vector_store_endpoints.py

@@ -3107,3 +3107,65 @@ class TestAzureAIAnalyzeNamedIndexClassification:
             user_api_key_dict=self._team_member("analyze", ["read"]),
         )
         assert result is True
+
+
+# ---------------------------------------------------------------------------
+# /vector_store/list — config-sourced entries must survive DB reconciliation.
+# Regression test for: config.yaml-loaded stores were pruned from the
+# in-memory registry on every list call because they had no DB row.
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_list_vector_stores_returns_config_sourced_and_leaves_registry_intact():
+    from litellm.proxy.vector_store_endpoints.management_endpoints import list_vector_stores
+    from litellm.vector_stores.vector_store_registry import VectorStoreRegistry
+
+    registry = VectorStoreRegistry()
+    registry.load_vector_stores_from_config(
+        [
+            {
+                "vector_store_name": "docs-kb",
+                "litellm_params": {
+                    "vector_store_id": "vs_from_config",
+                    "custom_llm_provider": "bedrock",
+                },
+            }
+        ]
+    )
+
+    original_registry = litellm.vector_store_registry
+    try:
+        litellm.vector_store_registry = registry
+
+        with (
+            # Empty DB — the store exists only in config/memory.
+            patch(
+                "litellm.vector_stores.vector_store_registry.VectorStoreRegistry._get_vector_stores_from_db",
+                new=AsyncMock(return_value=[]),
+            ),
+            patch("litellm.proxy.proxy_server.prisma_client", MagicMock()),
+            patch(
+                "litellm.proxy.vector_store_endpoints.management_endpoints._check_vector_store_access",
+                new=AsyncMock(return_value=True),
+            ),
+            patch(
+                "litellm.proxy.vector_store_endpoints.management_endpoints.check_feature_access_for_user",
+                new=AsyncMock(return_value=None),
+            ),
+        ):
+            response = await list_vector_stores(
+                user_api_key_dict=UserAPIKeyAuth(
+                    token="sk-test",
+                    key_name="sk-...test",
+                    user_role=LitellmUserRoles.PROXY_ADMIN,
+                ),
+            )
+
+        returned_ids = [vs["vector_store_id"] for vs in response.data]
+        assert "vs_from_config" in returned_ids
+        # And, critically, the registry must NOT have been mutated —
+        # config-loaded stores stay resident for downstream routing.
+        assert any(vs.get("vector_store_id") == "vs_from_config" for vs in registry.vector_stores)
+    finally:
+        litellm.vector_store_registry = original_registry