fix(engine): a Chrome shell that ignores SIGTERM can no longer freeze the CLI at launch (#6547)

The start probe waited for the shell to exit after SIGTERM, so a shell that stalled under load blocked the whole process. Kill it outright at the timeout.

packages/engine/src/services/chromeHostCeiling.test.ts

@@ -1,5 +1,8 @@
+import { chmodSync, mkdtempSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
 import { describe, expect, it } from "vitest";
-import { chromeMajorCeiling, exceedsChromeCeiling } from "./chromeHostCeiling.js";
+import { chromeMajorCeiling, exceedsChromeCeiling, shellStarts } from "./chromeHostCeiling.js";
 
 describe("chromeMajorCeiling", () => {
   it.each([
@@ -22,3 +25,19 @@ describe("exceedsChromeCeiling", () => {
     expect(exceedsChromeCeiling(name, ceiling)).toBe(expected);
   });
 });
+
+describe.skipIf(process.platform === "win32")("shellStarts", () => {
+  it("returns at its timeout even when the shell ignores SIGTERM", () => {
+    const dir = mkdtempSync(join(tmpdir(), "hf-shell-probe-"));
+    const binary = join(dir, "shell.sh");
+    writeFileSync(binary, "#!/bin/sh\ntrap '' TERM\nsleep 6\n");
+    chmodSync(binary, 0o755);
+    const started = Date.now();
+    try {
+      expect(shellStarts(binary, 300)).toBe(false);
+      expect(Date.now() - started).toBeLessThan(3000);
+    } finally {
+      rmSync(dir, { recursive: true, force: true });
+    }
+  });
+});

packages/engine/src/services/chromeHostCeiling.ts

@@ -64,11 +64,13 @@ const starts = new Map<string, boolean>();
 const debug = debuglog("hyperframes:browser");
 
 /** Whether a shell loads a blank page and exits: an old build can die at launch on a newer OS. Asked once per path. */
-export function shellStarts(binary: string): boolean {
+export function shellStarts(binary: string, timeoutMs = 10_000): boolean {
   let answer = starts.get(binary);
   if (answer === undefined) {
     const probe = ["--no-sandbox", "--dump-dom", "about:blank"];
-    answer = spawnSync(binary, probe, { stdio: "ignore", timeout: 10_000 })?.status === 0;
+    answer =
+      spawnSync(binary, probe, { stdio: "ignore", timeout: timeoutMs, killSignal: "SIGKILL" })
+        ?.status === 0;
     if (!answer) debug("skipping %s: it did not start", binary);
     starts.set(binary, answer);
   }