fix(scripts): kill boundary prep trees on windows

scripts/prepare-extension-package-boundary-artifacts.mjs

@@ -1,6 +1,6 @@
 // Prepares declaration and entry-shim artifacts that prove plugin package
 // boundary imports resolve through public package surfaces.
-import { spawn } from "node:child_process";
+import { spawn, spawnSync } from "node:child_process";
 import fs from "node:fs";
 import path, { resolve } from "node:path";
 import { isLocalCheckEnabled } from "./lib/local-heavy-check-runtime.mjs";
@@ -399,8 +399,16 @@ function abortSiblingSteps(abortController) {
   }
 }
 
-function signalNodeStep(child, signal) {
-  if (process.platform !== "win32" && typeof child.pid === "number") {
+export function signalNodeStep(
+  child,
+  signal,
+  {
+    platform = process.platform,
+    runTaskkill = spawnSync,
+    useProcessGroup = platform !== "win32",
+  } = {},
+) {
+  if (useProcessGroup && typeof child.pid === "number") {
     try {
       process.kill(-child.pid, signal);
       return;
@@ -408,6 +416,16 @@ function signalNodeStep(child, signal) {
       // The child process group can already be gone by the time cleanup runs.
     }
   }
+  if (platform === "win32" && typeof child.pid === "number") {
+    const args = ["/PID", String(child.pid), "/T"];
+    if (signal === "SIGKILL") {
+      args.push("/F");
+    }
+    const result = runTaskkill("taskkill", args, { stdio: "ignore" });
+    if (!result?.error && result?.status === 0) {
+      return;
+    }
+  }
   child.kill(signal);
 }
 
@@ -464,9 +482,10 @@ export function runNodeStep(label, args, timeoutMs, params = {}) {
     let killDeadlineAt = 0;
     const stdoutWriter = createPrefixedOutputWriter(label, process.stdout);
     const stderrWriter = createPrefixedOutputWriter(label, process.stderr);
-    const killNodeStep = (signal) => signalNodeStep(child, signal);
+    const useProcessGroup = process.platform !== "win32";
+    const killNodeStep = (signal) => signalNodeStep(child, signal, { useProcessGroup });
     const processGroupAlive = () => {
-      if (process.platform === "win32" || !child.pid) {
+      if (!useProcessGroup || !child.pid) {
         return false;
       }
       try {

test/scripts/prepare-extension-package-boundary-artifacts.test.ts

@@ -7,7 +7,7 @@ import os from "node:os";
 import path from "node:path";
 import { setTimeout as delay } from "node:timers/promises";
 import { pathToFileURL } from "node:url";
-import { afterEach, describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import {
   createPrefixedOutputWriter,
   isArtifactSetFresh,
@@ -17,6 +17,7 @@ import {
   runNodeStep,
   runNodeSteps,
   runNodeStepsInParallel,
+  signalNodeStep,
 } from "../../scripts/prepare-extension-package-boundary-artifacts.mjs";
 import { makeTempDir } from "../helpers/temp-dir.js";
 
@@ -123,6 +124,31 @@ describe("prepare-extension-package-boundary-artifacts", () => {
     expect(Date.now() - startedAt).toBeLessThan(abortBudgetMs);
   }, 45_000);
 
+  it("signals Windows node step process trees with taskkill", () => {
+    const child = {
+      kill: vi.fn(),
+      pid: 12345,
+    };
+    const runTaskkill = vi.fn(() => ({ error: undefined, status: 0 }));
+
+    signalNodeStep(child, "SIGTERM", {
+      platform: "win32",
+      runTaskkill,
+    });
+    expect(runTaskkill).toHaveBeenNthCalledWith(1, "taskkill", ["/PID", "12345", "/T"], {
+      stdio: "ignore",
+    });
+
+    signalNodeStep(child, "SIGKILL", {
+      platform: "win32",
+      runTaskkill,
+    });
+    expect(runTaskkill).toHaveBeenNthCalledWith(2, "taskkill", ["/PID", "12345", "/T", "/F"], {
+      stdio: "ignore",
+    });
+    expect(child.kill).not.toHaveBeenCalled();
+  });
+
   it.runIf(process.platform !== "win32")(
     "force-kills aborted sibling step process groups",
     async () => {