Python: Isolate MCP lifecycle task context

python/packages/core/agent_framework/_mcp.py

@@ -227,7 +227,7 @@ class MCPSpecificApproval(TypedDict, total=False):
     "_meta",
 })
 # object is a reference to the owner of the headers, so we keep track which headers belong to which tool
-_mcp_call_headers: ContextVar[tuple[object, dict[str, str]]] = ContextVar("_mcp_call_headers")
+_mcp_call_headers: ContextVar[tuple[object, dict[str, str]] | None] = ContextVar("_mcp_call_headers")
 _mcp_tool_runtime_context: ContextVar[tuple[object, Mapping[str, Any]] | None] = ContextVar(
     "_mcp_tool_runtime_context", default=None
 )
@@ -2010,10 +2010,14 @@ async def _ensure_lifecycle_owner(self) -> None:
                 return
 
             self._lifecycle_queue = asyncio.Queue()
-            self._lifecycle_owner_task = asyncio.create_task(
-                self._run_lifecycle_owner(),
-                name=f"mcp-lifecycle:{self.name}",
-            )
+            token = _mcp_call_headers.set(None)
+            try:
+                self._lifecycle_owner_task = asyncio.create_task(
+                    self._run_lifecycle_owner(),
+                    name=f"mcp-lifecycle:{self.name}",
+                )
+            finally:
+                _mcp_call_headers.reset(token)
 
     async def _run_lifecycle_owner(self) -> None:
         queue = self._lifecycle_queue

python/packages/core/tests/core/test_mcp.py

@@ -10740,6 +10740,35 @@ async def _pending_lifecycle_task_names() -> list[str]:
     return names
 
 
+async def test_lifecycle_owner_does_not_inherit_call_headers():
+    """Connection-lifetime work must not inherit headers from the call that starts it."""
+    from agent_framework._mcp import _mcp_call_headers
+
+    tool = MCPStreamableHTTPTool(name="context-check", url="https://mcp.example/mcp")
+    observed_call_headers: list[Any] = []
+    observed_request_context: list[str | None] = []
+    request_context = ContextVar[str]("request_context")
+
+    async def record_owner_context(**_: Any) -> None:
+        observed_call_headers.append(_mcp_call_headers.get(None))
+        observed_request_context.append(request_context.get(None))
+        tool.is_connected = True
+
+    call_headers_token = _mcp_call_headers.set((tool._header_request_owner, {"Authorization": "principal-a"}))
+    request_context_token = request_context.set("request-a")
+    try:
+        with patch.object(tool, "_connect_on_owner", new=record_owner_context):
+            await tool.connect()
+
+        assert observed_call_headers == [None]
+        assert observed_request_context == ["request-a"]
+    finally:
+        request_context.reset(request_context_token)
+        _mcp_call_headers.reset(call_headers_token)
+        tool.is_connected = False
+        await tool.close()
+
+
 async def test_failed_connect_stops_the_lifecycle_owner():
     """A connect that fails must not leave its owner task blocked on the queue forever."""
     client = _unauthorized_http_client()