Fix MCP client double initialize in config flow (#181594)

Co-authored-by: Home Assistant Developer <hello@home-assistant.io>

homeassistant/components/mcp/config_flow.py

@@ -117,8 +117,15 @@ async def validate_input(
     except vol.Invalid as error:
         raise InvalidUrl from error
     try:
-        async with mcp_client(hass, url, token_manager=token_manager) as session:
-            response = await session.initialize()
+        async with mcp_client(hass, url, token_manager=token_manager) as (
+            _session,
+            response,
+        ):
+            if not response.capabilities.tools:
+                raise MissingCapabilities(
+                    f"MCP Server {url} does not support 'Tools' capability"
+                )
+            return {"title": response.serverInfo.name}
     except httpx.TimeoutException as error:
         _LOGGER.info("Timeout connecting to MCP server: %s", error)
         raise TimeoutConnectError from error
@@ -132,13 +139,6 @@ async def validate_input(
         _LOGGER.info("Cannot connect to MCP server: %s", error)
         raise CannotConnect from error
 
-    if not response.capabilities.tools:
-        raise MissingCapabilities(
-            f"MCP Server {url} does not support 'Tools' capability"
-        )
-
-    return {"title": response.serverInfo.name}
-
 
 class ModelContextProtocolConfigFlow(AbstractOAuth2FlowHandler, domain=DOMAIN):
     """Handle a config flow for Model Context Protocol."""

homeassistant/components/mcp/coordinator.py

@@ -12,6 +12,7 @@ from mcp import McpError
 from mcp.client.session import ClientSession
 from mcp.client.sse import sse_client
 from mcp.client.streamable_http import streamable_http_client
+from mcp.types import InitializeResult
 from probatio import from_openapi
 import voluptuous as vol
 
@@ -65,7 +66,7 @@ async def mcp_client(
     hass: HomeAssistant,
     url: str,
     token_manager: TokenManager | None = None,
-) -> AsyncGenerator[ClientSession]:
+) -> AsyncGenerator[tuple[ClientSession, InitializeResult]]:
     """Create an MCP client.
 
     This is an asynccontext manager that exists to wrap other async context managers
@@ -84,8 +85,8 @@ async def mcp_client(
             ) as (read_stream, write_stream, _),
             ClientSession(read_stream, write_stream) as session,
         ):
-            await session.initialize()
-            yield session
+            result = await session.initialize()
+            yield session, result
     except ExceptionGroup as streamable_err:
         main_error = streamable_err.exceptions[0]
         # Method not Allowed likely means this is not a streamable HTTP server,
@@ -109,8 +110,8 @@ async def mcp_client(
                     ) as streams,
                     ClientSession(*streams) as session,
                 ):
-                    await session.initialize()
-                    yield session
+                    result = await session.initialize()
+                    yield session, result
             except ExceptionGroup as sse_err:
                 _LOGGER.debug("Error creating SSE MCP client: %s", sse_err)
                 raise sse_err.exceptions[0] from sse_err
@@ -149,9 +150,10 @@ class ModelContextProtocolTool(llm.Tool):
         """Call the tool."""
         try:
             async with asyncio.timeout(TIMEOUT):
-                async with mcp_client(
-                    hass, self.server_url, self.token_manager
-                ) as session:
+                async with mcp_client(hass, self.server_url, self.token_manager) as (
+                    session,
+                    _,
+                ):
                     result = await session.call_tool(
                         tool_input.tool_name, tool_input.tool_args
                     )
@@ -219,7 +221,7 @@ class ModelContextProtocolCoordinator(DataUpdateCoordinator[list[llm.Tool]]):
             async with asyncio.timeout(TIMEOUT):
                 async with mcp_client(
                     self.hass, self.config_entry.data[CONF_URL], self.token_manager
-                ) as session:
+                ) as (session, _):
                     result = await session.list_tools()
         except TimeoutError as error:
             _LOGGER.debug("Timeout when listing tools: %s", error)

tests/components/mcp/test_config_flow.py

@@ -119,6 +119,7 @@ async def test_form(
     assert result["result"].unique_id is None
 
     assert len(mock_setup_entry.mock_calls) == 1
+    mock_mcp_client.return_value.initialize.assert_called_once()
 
 
 @pytest.mark.parametrize(