fix(proxy): hydrate MCP server registry from DB on startup when store_model_in_db is false (#31775)

MCP servers created through the UI are persisted to the database independent of
store_model_in_db, but the in-memory registry that GET /v1/mcp/server reads was
hydrated from the database only through add_deployment, which runs solely when
store_model_in_db is True. On a DB-backed single-instance proxy with
store_model_in_db unset the registry started empty after a restart, so the MCP
Servers page showed nothing until an add or edit triggered a reload.

Hydrate the registry from the database on startup regardless of store_model_in_db
via a new ProxyConfig.init_mcp_servers_from_db, honoring supported_db_objects.

litellm/proxy/proxy_server.py

@@ -6314,6 +6314,10 @@ class ProxyConfig:
                 "litellm.proxy.proxy_server.py::ProxyConfig:_init_mcp_servers_in_db - {}".format(str(e))
             )
 
+    async def init_mcp_servers_from_db(self) -> None:
+        if self._should_load_db_object(object_type="mcp"):
+            await self._init_mcp_servers_in_db()
+
     async def _init_agents_in_db(self, prisma_client: PrismaClient):
         from litellm.proxy.agent_endpoints.agent_registry import (
             global_agent_registry as AGENT_REGISTRY,
@@ -7561,6 +7565,9 @@ class ProxyStartupEvent:
             )
             await proxy_config.get_credentials(prisma_client=prisma_client)
 
+        if store_model_in_db is not True:
+            await proxy_config.init_mcp_servers_from_db()
+
         await cls._initialize_slack_alerting_jobs(
             scheduler=scheduler,
             general_settings=general_settings,

tests/test_litellm/proxy/test_proxy_server.py

@@ -754,6 +754,66 @@ async def test_initialize_scheduled_jobs_credentials(monkeypatch):
         assert len(mock_scheduler_calls) > 0
 
 
+@pytest.mark.asyncio
+async def test_initialize_scheduled_jobs_hydrates_mcp_when_store_model_in_db_false(monkeypatch):
+    """
+    Regression (LIT-4128): MCP servers created via the UI are persisted to the DB
+    regardless of store_model_in_db, but the in-memory registry that GET
+    /v1/mcp/server reads is hydrated from the DB only by the store_model_in_db
+    model-sync loop (add_deployment). On a DB-backed proxy with store_model_in_db
+    unset the registry must still be hydrated on startup so previously-added
+    servers survive a restart instead of showing an empty list until a write.
+    """
+    monkeypatch.delenv("DISABLE_PRISMA_SCHEMA_UPDATE", raising=False)
+    monkeypatch.delenv("STORE_MODEL_IN_DB", raising=False)
+    from litellm.proxy.proxy_server import ProxyStartupEvent
+    from litellm.proxy.utils import ProxyLogging
+
+    mock_prisma_client = MagicMock()
+    mock_proxy_logging = MagicMock(spec=ProxyLogging)
+    mock_proxy_logging.slack_alerting_instance = MagicMock()
+    mock_proxy_config = AsyncMock()
+
+    with (
+        patch("litellm.proxy.proxy_server.proxy_config", mock_proxy_config),
+        patch("litellm.proxy.proxy_server.store_model_in_db", False),
+    ):
+        await ProxyStartupEvent.initialize_scheduled_background_jobs(
+            general_settings={},
+            prisma_client=mock_prisma_client,
+            proxy_budget_rescheduler_min_time=1,
+            proxy_budget_rescheduler_max_time=2,
+            proxy_batch_write_at=5,
+            proxy_logging_obj=mock_proxy_logging,
+        )
+
+    mock_proxy_config.add_deployment.assert_not_called()
+    mock_proxy_config.init_mcp_servers_from_db.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_init_mcp_servers_from_db_respects_supported_db_objects(monkeypatch):
+    """
+    init_mcp_servers_from_db hydrates MCP from the DB by default but skips it when
+    an explicit supported_db_objects allowlist omits "mcp".
+    """
+    from litellm.proxy.proxy_server import ProxyConfig
+
+    config = ProxyConfig()
+    with patch.object(config, "_init_mcp_servers_in_db", new=AsyncMock()) as mock_init:
+        monkeypatch.setattr("litellm.proxy.proxy_server.general_settings", {})
+        await config.init_mcp_servers_from_db()
+        mock_init.assert_awaited_once()
+
+        mock_init.reset_mock()
+        monkeypatch.setattr(
+            "litellm.proxy.proxy_server.general_settings",
+            {"supported_db_objects": ["models"]},
+        )
+        await config.init_mcp_servers_from_db()
+        mock_init.assert_not_awaited()
+
+
 def test_update_config_fields_deep_merge_db_wins():
     from litellm.proxy.proxy_server import ProxyConfig