[Feature][Responses API] Support MCP tool in background mode (#23494)

Signed-off-by: wuhang <wuhang6@huawei.com>

vllm/entrypoints/context.py

@@ -4,13 +4,15 @@ import json
 import logging
 from abc import ABC, abstractmethod
 from collections.abc import Sequence
-from typing import TYPE_CHECKING, Union
+from contextlib import AsyncExitStack
+from typing import TYPE_CHECKING, Optional, Union
 
 from openai_harmony import Author, Message, Role, StreamState, TextContent
 
 from vllm.entrypoints.harmony_utils import (
     get_encoding, get_streamable_parser_for_assistant, render_for_completion)
 from vllm.entrypoints.tool import Tool
+from vllm.entrypoints.tool_server import ToolServer
 from vllm.outputs import RequestOutput
 
 if TYPE_CHECKING:
@@ -37,6 +39,11 @@ class ConversationContext(ABC):
     def render_for_completion(self) -> list[int]:
         pass
 
+    @abstractmethod
+    async def init_tool_sessions(self, tool_server: Optional[ToolServer],
+                                 exit_stack: AsyncExitStack) -> None:
+        pass
+
 
 class SimpleContext(ConversationContext):
 
@@ -55,16 +62,21 @@ class SimpleContext(ConversationContext):
     def render_for_completion(self) -> list[int]:
         raise NotImplementedError("Should not be called.")
 
+    async def init_tool_sessions(self, tool_server: Optional[ToolServer],
+                                 exit_stack: AsyncExitStack) -> None:
+        pass
+
 
 class HarmonyContext(ConversationContext):
 
     def __init__(
         self,
         messages: list,
-        tool_sessions: dict[str, Tool],
+        available_tools: list[str],
     ):
         self._messages = messages
-        self.tool_sessions = tool_sessions
+        self.available_tools = available_tools
+        self._tool_sessions: dict[str, Union[ClientSession, Tool]] = {}
 
         self.parser = get_streamable_parser_for_assistant()
         self.num_init_messages = len(messages)
@@ -116,10 +128,10 @@ class HarmonyContext(ConversationContext):
         if recipient is not None:
             if recipient.startswith("browser."):
                 return await self.call_search_tool(
-                    self.tool_sessions["browser"], last_msg)
+                    self._tool_sessions["browser"], last_msg)
             elif recipient.startswith("python"):
                 return await self.call_python_tool(
-                    self.tool_sessions["python"], last_msg)
+                    self._tool_sessions["python"], last_msg)
         raise ValueError("No tool call found")
 
     def render_for_completion(self) -> list[int]:
@@ -161,6 +173,15 @@ class HarmonyContext(ConversationContext):
                     recipient=Role.ASSISTANT)
         ]
 
+    async def init_tool_sessions(self, tool_server: Optional[ToolServer],
+                                 exit_stack: AsyncExitStack) -> None:
+        if tool_server:
+            for tool_name in self.available_tools:
+                if tool_name not in self._tool_sessions:
+                    self._tool_sessions[
+                        tool_name] = await exit_stack.enter_async_context(
+                            tool_server.new_session(tool_name))
+
 
 class StreamingHarmonyContext(HarmonyContext):