Root cause: fuser-based EADDRINUSE handler killed the current process
due to a race condition during systemd restart cycles. The fuser command
returned the current PID because the socket was half-open, and the guard
condition (p !== process.pid) failed to filter it.
Additionally, two competing systemd services (system-level and user-level)
created a restart war where each instance killed the other.
Fix approach (inspired by Next.js, Vite, webpack-dev-server):
- Replace fuser with net.createServer port probe (no external commands)
- PID-file based stale detection + ss fallback for orphan detection
- Wait loop with 300ms polling after SIGTERM to stale process
- Single-service architecture (disabled user-level unit)
Tested: 5 consecutive rapid restarts, 8+ minute uptime, zero crashes.
Co-Authored-By: zcode <noreply@zcode.dev>
