fix(qa): taskkill lifecycle probe trees on windows

test/e2e/qa-lab/plugins/plugin-lifecycle-probe-runtime.ts

@@ -1,5 +1,5 @@
 // Plugin Lifecycle Probe tests cover QA Lab plugin lifecycle evidence.
-import { spawn } from "node:child_process";
+import { spawn, spawnSync } from "node:child_process";
 import { randomBytes } from "node:crypto";
 import fs from "node:fs";
 import os from "node:os";
@@ -17,6 +17,7 @@ interface CommandOptions {
   env?: NodeJS.ProcessEnv;
   outputFile?: string;
   spawnImpl?: typeof spawn;
+  taskkillImpl?: typeof spawnSync;
   timeoutKillGraceMs?: number;
   timeoutMs?: number;
 }
@@ -266,6 +267,26 @@ async function runCommand(command: string, args: readonly string[], options: Com
             // The process group may already be gone; fall back to the direct child.
           }
         }
+        if (!useProcessGroup && child.pid) {
+          const runTaskkill = options.taskkillImpl ?? spawnSync;
+          const args = ["/PID", String(child.pid), "/T"];
+          if (signal === "SIGKILL") {
+            args.push("/F");
+          }
+          const result = runTaskkill("taskkill", args, { stdio: "ignore", windowsHide: true });
+          if (!result.error && result.status === 0) {
+            return;
+          }
+          if (signal !== "SIGKILL") {
+            const forceResult = runTaskkill("taskkill", [...args, "/F"], {
+              stdio: "ignore",
+              windowsHide: true,
+            });
+            if (!forceResult.error && forceResult.status === 0) {
+              return;
+            }
+          }
+        }
         child.kill(signal);
       };
       const isProcessGroupRunning = () => {

test/e2e/qa-lab/plugins/plugin-lifecycle-probe.e2e.test.ts

@@ -136,6 +136,50 @@ describe("plugin lifecycle matrix probe", () => {
     }
   });
 
+  it("force-kills timed Windows commands with taskkill when graceful taskkill fails", async () => {
+    vi.useFakeTimers();
+    const platformDescriptor = Object.getOwnPropertyDescriptor(process, "platform");
+    Object.defineProperty(process, "platform", { value: "win32", configurable: true });
+    try {
+      const child = Object.assign(new FakeCommandChild(), { pid: 12345 });
+      const taskkillImpl = vi
+        .fn()
+        .mockReturnValueOnce({ status: 1 })
+        .mockImplementationOnce(() => {
+          queueMicrotask(() => child.emit("exit", null, "SIGTERM"));
+          return { status: 0 };
+        });
+      const runPromise = probeTesting.runCommand("fake-command", ["install"], {
+        spawnImpl: (() => child) as unknown as typeof import("node:child_process").spawn,
+        taskkillImpl,
+        timeoutKillGraceMs: 100,
+        timeoutMs: 10,
+      });
+      const runError = runPromise.catch((error: unknown) => error);
+
+      await vi.advanceTimersByTimeAsync(10);
+
+      expect(taskkillImpl).toHaveBeenNthCalledWith(1, "taskkill", ["/PID", "12345", "/T"], {
+        stdio: "ignore",
+        windowsHide: true,
+      });
+      expect(taskkillImpl).toHaveBeenNthCalledWith(2, "taskkill", ["/PID", "12345", "/T", "/F"], {
+        stdio: "ignore",
+        windowsHide: true,
+      });
+      expect(child.signals).toEqual([]);
+
+      const error = await runError;
+      expect(error).toBeInstanceOf(Error);
+      expect((error as Error).message).toBe("fake-command install timed out after 10ms");
+    } finally {
+      if (platformDescriptor) {
+        Object.defineProperty(process, "platform", platformDescriptor);
+      }
+      vi.useRealTimers();
+    }
+  });
+
   it("keeps fallback SIGKILL armed for ignored-stdio descendants", async () => {
     if (process.platform === "win32") {
       return;