fix(bench): kill gateway child trees on windows

test/scripts/bench-gateway-child-test-support.ts

@@ -1,4 +1,5 @@
 // Gateway benchmark child test support simulates child process behavior for script tests.
+import type { spawnSync } from "node:child_process";
 import { EventEmitter } from "node:events";
 import { expect, it, vi } from "vitest";
 
@@ -10,7 +11,12 @@ type StopChildResult = {
 
 type StopChild<TChild> = (
   child: TChild,
-  options?: { killGraceMs?: number; teardownGraceMs?: number },
+  options?: {
+    killGraceMs?: number;
+    platform?: NodeJS.Platform;
+    runTaskkill?: typeof spawnSync;
+    teardownGraceMs?: number;
+  },
 ) => Promise<StopChildResult>;
 
 export function registerStopChildBehaviorTests<TChild>(params: {
@@ -101,6 +107,52 @@ export function registerStopChildBehaviorTests<TChild>(params: {
     expect(child.unref).toHaveBeenCalledOnce();
   });
 
+  it("signals Windows child process trees with taskkill", async () => {
+    const child = new EventEmitter() as EventEmitter & {
+      exitCode: number | null;
+      kill: ReturnType<typeof vi.fn>;
+      pid: number;
+      signalCode: NodeJS.Signals | null;
+      stderr: { destroy: ReturnType<typeof vi.fn> };
+      stdin: { destroy: ReturnType<typeof vi.fn> };
+      stdout: { destroy: ReturnType<typeof vi.fn> };
+      unref: ReturnType<typeof vi.fn>;
+    };
+    child.exitCode = null;
+    child.kill = vi.fn(() => true);
+    child.pid = 4450;
+    child.signalCode = null;
+    child.stderr = { destroy: vi.fn() };
+    child.stdin = { destroy: vi.fn() };
+    child.stdout = { destroy: vi.fn() };
+    child.unref = vi.fn();
+    const runTaskkill = vi.fn(() => ({ error: undefined, status: 0 }));
+
+    await expect(
+      params.stopChild(child as unknown as TChild, {
+        killGraceMs: 1,
+        platform: "win32",
+        runTaskkill,
+        teardownGraceMs: 1,
+      }),
+    ).resolves.toEqual({
+      exitedBeforeTeardown: false,
+      exitCode: null,
+      signal: "SIGKILL",
+    });
+    expect(runTaskkill).toHaveBeenNthCalledWith(1, "taskkill", ["/PID", "4450", "/T"], {
+      stdio: "ignore",
+    });
+    expect(runTaskkill).toHaveBeenNthCalledWith(2, "taskkill", ["/PID", "4450", "/T", "/F"], {
+      stdio: "ignore",
+    });
+    expect(child.kill).not.toHaveBeenCalled();
+    expect(child.stdin.destroy).toHaveBeenCalledOnce();
+    expect(child.stdout.destroy).toHaveBeenCalledOnce();
+    expect(child.stderr.destroy).toHaveBeenCalledOnce();
+    expect(child.unref).toHaveBeenCalledOnce();
+  });
+
   it.skipIf(process.platform === "win32")(
     "preserves pre-teardown wrapper exits while cleaning the process group",
     async () => {
@@ -144,9 +196,7 @@ export function registerStopChildBehaviorTests<TChild>(params: {
           child.exitCode = 0;
           child.emit("exit", 0, null);
         });
-        await expect(
-          stopped,
-        ).resolves.toEqual({
+        await expect(stopped).resolves.toEqual({
           exitedBeforeTeardown: true,
           exitCode: 0,
           signal: null,