browse/test/chromium-profile-isolation.test.ts: 2 of 9 cases fail on macOS — afterEach kill(-pgid) throws EPERM on an already-dead daemon #2908

Version: v1.87.2.0 (#2874) through v1.87.4.0 (a6b3a57). Platform: macOS 26 (Darwin 25.6.0), Bun 1.4.2. CI (ubuntu) is green.

Two cases fail deterministically on a Mac, every run:

✗ browse/test/chromium-profile-isolation.test.ts — Chromium profile isolation (#2817) > headless --force-restart stop preserves another project's headed profile
✗ browse/test/chromium-profile-isolation.test.ts — Chromium profile isolation (#2817) > headless disconnect preserves another project's headed profile
SystemError: kill() failed: EPERM: Operation not permitted
  at safeKill (lib/error-handling.ts:31)
  at afterEach (browse/test/chromium-profile-isolation.test.ts:52)

Both cases stop the daemon in the test body (--force-restart stop / disconnect), then afterEach does safeKill(-daemonPid, 'SIGKILL') on the whole process group. On macOS, kill(-pgid) on a group that no longer exists returns EPERM; Linux returns ESRCH. safeKill only swallows ESRCH, so the cleanup throws after the assertions already passed.

Diagnostic (not a patch proposal): wrapping the group kill in try/catch and logging shows isProcessAlive(daemonPid) === false, ps -p empty, and a direct kill(daemonPid) fine. With that throw tolerated: 9 pass / 0 fail.

Suggested fix: have safeKill (or just this afterEach) treat EPERM the same as ESRCH when the target is a negative pgid and the pid is no longer alive, or skip the group kill when the body already stopped the daemon.