Function startPpidWatchdog

src/mcp/proxy.ts:548–570

* PPID watchdog mirroring the one in `MCPServer.start` — kills the proxy if * the MCP host (or its proxy of a host, see HOST_PPID_ENV) goes away without * closing stdin. Issue #277 documents why we can't rely on stdin EOF on * Linux: the parent may be SIGKILL'd and reparenting doesn't close pipes

(socket: net.Socket)

 * watchers to clean up, so this is cheap.
 */
function startPpidWatchdog(socket: net.Socket): void {
  const pollMs = parsePollMs(process.env.CODEGRAPH_PPID_POLL_MS);
  if (pollMs <= 0) return;
  // Baseline from the CLI entry's earliest capture, not process.ppid here —
  // a launcher killed during our first ~100ms would otherwise leave the
  // baseline at 1 and blind the divergence check forever (#1185).
  const originalPpid = EARLY_PPID;
  const hostPpid = parseHostPpid(process.env[HOST_PPID_ENV]);
  const timer = setInterval(() => {
    const reason = supervisionLostReason({
      originalPpid,
      currentPpid: process.ppid,
      hostPpid,
      isAlive: isProcessAliveLocal,
    });
    if (reason) {
      process.stderr.write(`[CodeGraph MCP] Parent process exited (${reason}); shutting down.\n`);
      try { socket.destroy(); } catch { /* ignore */ }
      process.exit(0);
    }
  }, pollMs);
  timer.unref?.();
}

function parsePollMs(raw: string | undefined): number {
  if (raw === undefined || raw === '') return DEFAULT_PPID_POLL_MS;