Fix CI: coverage, ruff format, and remove unused handle_list_tools

- Add anyio.sleep(0) between terminate() and cancel_scope.cancel() so
  the message router can observe the ClosedResourceError from the closed
  streams before the task group is cancelled (restores line 1022 coverage)
- Remove handle_list_tools from test — it was never called (only
  call_tool is exercised), so its return was an uncovered line
- Mark the CallToolResult return as pragma: no cover — intentionally
  unreachable in this test because the task is always cancelled at
  await tool_gate.wait() before the return executes
- Collapse multi-line function signatures to satisfy ruff-format

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: wiggzz

src/mcp/server/streamable_http_manager.py

@@ -193,6 +193,9 @@ async def run_request_handler(*, task_status: TaskStatus[None] = anyio.TASK_STAT
                 await http_transport.handle_request(scope, receive, send)
                 # Terminate the transport after the request is handled
                 await http_transport.terminate()
+                # Yield one scheduling step so other tasks (e.g. the message
+                # router) can observe the closed streams before we cancel.
+                await anyio.sleep(0)
                 # Cancel the request-scoped task group to stop the server task
                 request_tg.cancel_scope.cancel()
 

tests/server/test_streamable_http_manager.py

@@ -292,24 +292,13 @@ async def test_stateless_requests_task_leak_on_client_disconnect():
     tool_started = anyio.Event()
     tool_gate = anyio.Event()
 
-    async def handle_list_tools(
-        ctx: ServerRequestContext, params: PaginatedRequestParams | None
-    ) -> ListToolsResult:
-        return ListToolsResult(
-            tools=[Tool(name="slow_tool", description="A slow tool", inputSchema={"type": "object"})]
-        )
-
-    async def handle_call_tool(
-        ctx: ServerRequestContext, params: Any
-    ) -> CallToolResult:
+    async def handle_call_tool(ctx: ServerRequestContext, params: Any) -> CallToolResult:
         tool_started.set()
-        # Simulate a slow tool (e.g., API call to Discovery/Snowflake)
         await tool_gate.wait()
-        return CallToolResult(content=[TextContent(type="text", text="done")])
+        return CallToolResult(content=[TextContent(type="text", text="done")])  # pragma: no cover
 
     app = Server(
         "test-stateless-leak",
-        on_list_tools=handle_list_tools,
         on_call_tool=handle_call_tool,
     )