feat: enable MCP execution in Responses impl (#2240)

## Test Plan

```
pytest -s -v 'tests/verifications/openai_api/test_responses.py' \
  --provider=stack:together --model meta-llama/Llama-4-Scout-17B-16E-Instruct
```

tests/integration/tool_runtime/test_registration.py

@@ -4,120 +4,54 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-import socket
-import threading
-import time
-
-import httpx
-import mcp.types as types
 import pytest
-import uvicorn
-from mcp.server.fastmcp import Context, FastMCP
-from mcp.server.sse import SseServerTransport
-from starlette.applications import Starlette
-from starlette.routing import Mount, Route
+
+from llama_stack import LlamaStackAsLibraryClient
+from tests.common.mcp import MCP_TOOLGROUP_ID, make_mcp_server
 
 
-@pytest.fixture(scope="module")
-def mcp_server():
-    server = FastMCP("FastMCP Test Server")
+def test_register_and_unregister_toolgroup(llama_stack_client):
+    # TODO: make this work for http client also but you need to ensure
+    # the MCP server is reachable from llama stack server
+    if not isinstance(llama_stack_client, LlamaStackAsLibraryClient):
+        pytest.skip("The local MCP server only reliably reachable from library client.")
 
-    @server.tool()
-    async def fetch(url: str, ctx: Context) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
-        headers = {"User-Agent": "MCP Test Server (github.com/modelcontextprotocol/python-sdk)"}
-        async with httpx.AsyncClient(follow_redirects=True, headers=headers) as client:
-            response = await client.get(url)
-            response.raise_for_status()
-            return [types.TextContent(type="text", text=response.text)]
-
-    sse = SseServerTransport("/messages/")
-
-    async def handle_sse(request):
-        async with sse.connect_sse(request.scope, request.receive, request._send) as streams:
-            await server._mcp_server.run(
-                streams[0],
-                streams[1],
-                server._mcp_server.create_initialization_options(),
-            )
-
-    app = Starlette(
-        debug=True,
-        routes=[
-            Route("/sse", endpoint=handle_sse),
-            Mount("/messages/", app=sse.handle_post_message),
-        ],
-    )
-
-    def get_open_port():
-        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
-            sock.bind(("", 0))
-            return sock.getsockname()[1]
-
-    port = get_open_port()
-
-    def run_server():
-        uvicorn.run(app, host="0.0.0.0", port=port)
-
-    # Start the server in a new thread
-    server_thread = threading.Thread(target=run_server, daemon=True)
-    server_thread.start()
-
-    # Polling until the server is ready
-    timeout = 10
-    start_time = time.time()
-
-    while time.time() - start_time < timeout:
-        try:
-            response = httpx.get(f"http://localhost:{port}/sse")
-            if response.status_code == 200:
-                break
-        except (httpx.RequestError, httpx.HTTPStatusError):
-            pass
-        time.sleep(0.1)
-
-    yield port
-
-
-def test_register_and_unregister_toolgroup(llama_stack_client, mcp_server):
-    """
-    Integration test for registering and unregistering a toolgroup using the ToolGroups API.
-    """
-    port = mcp_server
-    test_toolgroup_id = "remote::web-fetch"
+    test_toolgroup_id = MCP_TOOLGROUP_ID
     provider_id = "model-context-protocol"
 
-    # Cleanup before running the test
-    toolgroups = llama_stack_client.toolgroups.list()
-    for toolgroup in toolgroups:
-        if toolgroup.identifier == test_toolgroup_id:
-            llama_stack_client.toolgroups.unregister(toolgroup_id=test_toolgroup_id)
+    with make_mcp_server() as mcp_server_info:
+        # Cleanup before running the test
+        toolgroups = llama_stack_client.toolgroups.list()
+        for toolgroup in toolgroups:
+            if toolgroup.identifier == test_toolgroup_id:
+                llama_stack_client.toolgroups.unregister(toolgroup_id=test_toolgroup_id)
 
-    # Register the toolgroup
-    llama_stack_client.toolgroups.register(
-        toolgroup_id=test_toolgroup_id,
-        provider_id=provider_id,
-        mcp_endpoint=dict(uri=f"http://localhost:{port}/sse"),
-    )
+        # Register the toolgroup
+        llama_stack_client.toolgroups.register(
+            toolgroup_id=test_toolgroup_id,
+            provider_id=provider_id,
+            mcp_endpoint=dict(uri=mcp_server_info["server_url"]),
+        )
 
-    # Verify registration
-    registered_toolgroup = llama_stack_client.toolgroups.get(toolgroup_id=test_toolgroup_id)
-    assert registered_toolgroup is not None
-    assert registered_toolgroup.identifier == test_toolgroup_id
-    assert registered_toolgroup.provider_id == provider_id
+        # Verify registration
+        registered_toolgroup = llama_stack_client.toolgroups.get(toolgroup_id=test_toolgroup_id)
+        assert registered_toolgroup is not None
+        assert registered_toolgroup.identifier == test_toolgroup_id
+        assert registered_toolgroup.provider_id == provider_id
 
-    # Verify tools listing
-    tools_list_response = llama_stack_client.tools.list(toolgroup_id=test_toolgroup_id)
-    assert isinstance(tools_list_response, list)
-    assert tools_list_response
+        # Verify tools listing
+        tools_list_response = llama_stack_client.tools.list(toolgroup_id=test_toolgroup_id)
+        assert isinstance(tools_list_response, list)
+        assert tools_list_response
 
-    # Unregister the toolgroup
-    llama_stack_client.toolgroups.unregister(toolgroup_id=test_toolgroup_id)
+        # Unregister the toolgroup
+        llama_stack_client.toolgroups.unregister(toolgroup_id=test_toolgroup_id)
 
-    # Verify it is unregistered
-    with pytest.raises(Exception, match=f"Tool group '{test_toolgroup_id}' not found"):
-        llama_stack_client.toolgroups.get(toolgroup_id=test_toolgroup_id)
+        # Verify it is unregistered
+        with pytest.raises(Exception, match=f"Tool group '{test_toolgroup_id}' not found"):
+            llama_stack_client.toolgroups.get(toolgroup_id=test_toolgroup_id)
 
-    # Verify tools are also unregistered
-    unregister_tools_list_response = llama_stack_client.tools.list(toolgroup_id=test_toolgroup_id)
-    assert isinstance(unregister_tools_list_response, list)
-    assert not unregister_tools_list_response
+        # Verify tools are also unregistered
+        unregister_tools_list_response = llama_stack_client.tools.list(toolgroup_id=test_toolgroup_id)
+        assert isinstance(unregister_tools_list_response, list)
+        assert not unregister_tools_list_response