Fix MCP client double initialize in config flow

homeassistant/components/mcp/config_flow.py

@@ -151,8 +151,11 @@ 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,
+        ):
+            pass
     except httpx.TimeoutException as error:
         _LOGGER.info("Timeout connecting to MCP server: %s", error)
         raise TimeoutConnectError from error

homeassistant/components/mcp/coordinator.py

@@ -11,6 +11,7 @@
 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
 import voluptuous as vol
 from voluptuous_openapi import convert_to_voluptuous
 
@@ -38,7 +39,7 @@ 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
@@ -57,8 +58,8 @@ 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,
@@ -78,8 +79,8 @@ async def mcp_client(
                     sse_client(url=url, headers=headers) 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
@@ -115,9 +116,10 @@ async def async_call(
         """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
                     )
@@ -161,7 +163,7 @@ async def _async_update_data(self) -> 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

@@ -120,6 +120,32 @@ async def test_form(
     assert len(mock_setup_entry.mock_calls) == 1
 
 
+async def test_initialize_called_once_in_config_flow(
+    hass: HomeAssistant, mock_setup_entry: AsyncMock, mock_mcp_client: Mock
+) -> None:
+    """Test that initialize is called exactly once during the config flow.
+
+    Regression test for the double-initialize bug: the mcp_client context
+    manager calls initialize() before yielding the session, and validate_input
+    previously called it a second time. MCP servers reject the second call with
+    -32600 "Invalid Request: Server already initialized".
+    """
+    response = Mock()
+    response.serverInfo.name = TEST_API_NAME
+    mock_mcp_client.return_value.initialize.return_value = response
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": config_entries.SOURCE_USER}
+    )
+    result = await hass.config_entries.flow.async_configure(
+        result["flow_id"],
+        {CONF_URL: MCP_SERVER_URL},
+    )
+
+    assert result["type"] is FlowResultType.CREATE_ENTRY
+    mock_mcp_client.return_value.initialize.assert_called_once()
+
+
 @pytest.mark.parametrize(
     ("side_effect", "expected_error"),
     [