test(gateway): pin MCP loopback drain proof to a server-side barrier (#117181)

The drain test asserted "close has not settled" after a fixed 20ms sleep.
Node only exempts a connection from close()'s idle sweep once its parser has
begun a message, so a client-side connect barrier let a loaded machine reach
close() before the server parsed the request: the socket was swept as idle,
the client saw ECONNRESET, and the drain settled inside the window.

Wait on capture admission (onRequestStart) instead, which fires server-side
after the headers are accepted, and move the assertion to just before the
successor is used so it proves the successor was minted mid-drain.

src/gateway/mcp-http.test.ts

@@ -3413,13 +3413,22 @@ describe("createMcpLoopbackServerConfig", () => {
     if (!oldRuntime) {
       throw new Error("expected old MCP loopback runtime");
     }
-    let stalledRequest: ReturnType<typeof request> | undefined;
-    let resolveSocketReady: () => void = () => {};
-    let rejectSocketReady: (error: Error) => void = () => {};
-    const socketReady = new Promise<void>((resolve, reject) => {
-      resolveSocketReady = resolve;
-      rejectSocketReady = reject;
+    // Node only exempts a connection from close()'s idle sweep once its parser has
+    // begun a message, so the drain is pinned by the server-side request start, not
+    // by the client-side connect. Capture admission is that server-side signal.
+    const captureKey = "capture-stalled-drain";
+    let resolveRequestStarted: () => void = () => {};
+    let rejectRequestStarted: (error: Error) => void = () => {};
+    const requestStarted = new Promise<void>((resolve, reject) => {
+      resolveRequestStarted = resolve;
+      rejectRequestStarted = reject;
     });
+    beginMcpLoopbackToolCallCapture({
+      captureKey,
+      onRequestStart: () => resolveRequestStarted(),
+      onToolCallResult: vi.fn(),
+    });
+    let stalledRequest: ReturnType<typeof request> | undefined;
     const responsePromise = new Promise<void>((resolve, reject) => {
       const req = request(
         {
@@ -3431,6 +3440,7 @@ describe("createMcpLoopbackServerConfig", () => {
             authorization: `Bearer ${oldRuntime.ownerToken}`,
             connection: "close",
             "content-type": "application/json",
+            "x-openclaw-cli-capture-key": captureKey,
           },
         },
         (res) => {
@@ -3438,15 +3448,8 @@ describe("createMcpLoopbackServerConfig", () => {
           res.once("end", resolve);
         },
       );
-      req.once("socket", (socket) => {
-        if (!socket.connecting) {
-          resolveSocketReady();
-          return;
-        }
-        socket.once("connect", resolveSocketReady);
-      });
       req.once("error", (error) => {
-        rejectSocketReady(error);
+        rejectRequestStarted(error);
         reject(error);
       });
       req.write("{");
@@ -3462,20 +3465,13 @@ describe("createMcpLoopbackServerConfig", () => {
     };
     let oldClose: Promise<void> | undefined;
     try {
-      await socketReady;
-      await new Promise<void>((resolve) => {
-        setImmediate(resolve);
-      });
+      await requestStarted;
 
       let closeSettled = false;
       oldClose = closeMcpLoopbackServer().finally(() => {
         closeSettled = true;
       });
       expect(getActiveMcpLoopbackRuntime()).toBeUndefined();
-      await new Promise<void>((resolve) => {
-        setTimeout(resolve, 20);
-      });
-      expect(closeSettled).toBe(false);
 
       const successor = await startLoopbackServerForTest();
       const successorGrant = mintMcpLoopbackClientGrant({
@@ -3487,6 +3483,9 @@ describe("createMcpLoopbackServerConfig", () => {
         runtimeOwnerToken: successor.runtime.ownerToken,
         captureKey: "capture-successor",
       });
+      // The unfinished body still holds the old connection, so the successor was
+      // minted mid-drain: exactly the window where a late close could fence it.
+      expect(closeSettled).toBe(false);
 
       finishStalledRequest();
       await responsePromise;
@@ -3503,6 +3502,7 @@ describe("createMcpLoopbackServerConfig", () => {
         ).status,
       ).toBe(200);
     } finally {
+      clearMcpLoopbackToolCallCapture(captureKey);
       finishStalledRequest();
       await responsePromise.catch(() => undefined);
       await (oldClose ?? oldServer.close()).catch(() => undefined);