fix(gateway): detect launchd for restart service path

[oddrap]

Summary

• Detect macOS launchd-managed gateway processes via XPC_SERVICE_NAME when handling /restart.
• Route launchd-managed gateway restarts through the existing service restart path (via_service=True) instead of detached restart.
• Add regression coverage for launchd and tighten the detached-path test to require no service manager env.

Root cause

On macOS, Hermes Gateway runs under launchd. launchd sets XPC_SERVICE_NAME, not systemd's INVOCATION_ID. Without recognizing launchd, /restart falls through to the detached restart path and can exit cleanly without launchd relaunching the gateway.

Verification

• ./venv/bin/python -m pytest tests/gateway/test_restart_notification.py -q -o 'addopts=' → 26 passed
• ./venv/bin/python -m py_compile gateway/run.py tests/gateway/test_restart_notification.py
• git diff --check

Related: #29180

[alt-glitch]

Duplicate/competing: Competing fix in the launchd restart cluster — same XPC_SERVICE_NAME detection as #19940, #24898, #33393. More comprehensive approach in #34230/#34988. Also see merged #28341.

[teknium1]

Thanks for the focused launchd restart fix. This is already implemented on current main by a later, stronger version of the same approach.

Automated hermes-sweeper review evidence:

• gateway/slash_commands.py:1302 detects launchd through XPC_SERVICE_NAME and routes the restart through request_restart(detached=False, via_service=True).
• The merged implementation deliberately excludes XPC_SERVICE_NAME="0", which interactive macOS shells inherit; treating it as launchd would incorrectly take the service path without a supervisor.
• tests/gateway/test_restart_service_detection.py:46 covers both a launchd job label and the "0" interactive-shell sentinel.
• The implementation landed in abc3662bf6076045e4d4dc1e14a74cb35d69b86e (fix(gateway): detect launchd in /restart service-manager probe (#43475)) and is contained in v2026.7.1.

This also matches the duplicate/competing-fix context noted by @alt-glitch.