feat(70): add Linux systemd user unit service support

Add systemd --user service management alongside existing launchd (macOS)
and Task Scheduler (Windows). Includes Docker detection, linger hint,
OCX_SERVICE=1 parity, and log routing to ~/.opencodex/service.log.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: lidge-jun

src/service.ts

@@ -1,7 +1,7 @@
 /**
  * `ocx service` — run the proxy as a background service that auto-starts on login and
- * auto-restarts on crash. macOS → launchd LaunchAgent; Windows → Task Scheduler.
- * The plist/task sets OCX_SERVICE=1 so the proxy's shutdown handler does NOT restore native
+ * auto-restarts on crash. macOS → launchd; Windows → Task Scheduler; Linux → systemd user unit.
+ * The service sets OCX_SERVICE=1 so the proxy's shutdown handler does NOT restore native
  * Codex on a service-managed restart (the restarted instance re-injects); explicit stop/uninstall
  * restore it via the command.
  */
@@ -91,35 +91,113 @@ function stopWindows(): void { try { sh(`schtasks /end /tn ${TASK}`); } catch {
 function statusWindows(): string { try { return sh(`schtasks /query /tn ${TASK}`); } catch { return ""; } }
 function uninstallWindows(): void { try { sh(`schtasks /delete /tn ${TASK} /f`); } catch { /* absent */ } }
 
+// ── Linux (systemd user unit) ──
+function unitDir(): string {
+  return join(homedir(), ".config", "systemd", "user");
+}
+
+function unitPath(): string {
+  return join(unitDir(), `${TASK}.service`);
+}
+
+export function buildUnit(): string {
+  const { bun, cli } = cliEntry();
+  const log = logPath();
+  const path = process.env.PATH ?? "/usr/local/bin:/usr/bin:/bin";
+  return `[Unit]
+Description=OpenCodex Proxy Server
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=${bun} ${cli} start
+Restart=on-failure
+RestartSec=5
+Environment=OCX_SERVICE=1
+Environment=PATH=${path}
+StandardOutput=append:${log}
+StandardError=append:${log}
+
+[Install]
+WantedBy=default.target
+`;
+}
+
+function isSystemd(): boolean {
+  try { execSync("systemctl --version", { stdio: "pipe" }); return true; } catch { return false; }
+}
+
+function installSystemd(): void {
+  const dir = unitDir();
+  if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
+  if (!existsSync(getConfigDir())) mkdirSync(getConfigDir(), { recursive: true });
+  writeFileSync(unitPath(), buildUnit(), "utf8");
+  sh("systemctl --user daemon-reload");
+  sh(`systemctl --user enable --now ${TASK}`);
+}
+function startSystemd(): void { sh(`systemctl --user start ${TASK}`); }
+function stopSystemd(): void { try { sh(`systemctl --user stop ${TASK}`); } catch { /* not running */ } }
+function statusSystemd(): string { try { return sh(`systemctl --user status ${TASK}`); } catch { return ""; } }
+function uninstallSystemd(): void {
+  try { sh(`systemctl --user disable --now ${TASK}`); } catch { /* absent */ }
+  if (existsSync(unitPath())) unlinkSync(unitPath());
+  try { sh("systemctl --user daemon-reload"); } catch { /* best-effort */ }
+}
+
+type ServiceOps = {
+  install: () => void; start: () => void; stop: () => void;
+  status: () => string; uninstall: () => void;
+};
+
+function platformOps(): ServiceOps | null {
+  if (process.platform === "darwin")
+    return { install: installLaunchd, start: startLaunchd, stop: stopLaunchd, status: statusLaunchd, uninstall: uninstallLaunchd };
+  if (process.platform === "win32")
+    return { install: installWindows, start: startWindows, stop: stopWindows, status: statusWindows, uninstall: uninstallWindows };
+  if (process.platform === "linux") {
+    if (existsSync("/.dockerenv")) {
+      console.error("Docker detected. Run 'ocx start' directly instead of using the service manager.");
+      process.exit(1);
+    }
+    if (!isSystemd()) {
+      console.error("systemd not found. Run 'ocx start' under your process supervisor.");
+      process.exit(1);
+    }
+    return { install: installSystemd, start: startSystemd, stop: stopSystemd, status: statusSystemd, uninstall: uninstallSystemd };
+  }
+  return null;
+}
+
 export function serviceCommand(sub?: string): void {
-  const mac = process.platform === "darwin";
-  const win = process.platform === "win32";
-  if (!mac && !win) {
-    console.error("ocx service supports macOS (launchd) and Windows (Task Scheduler). On Linux, run 'ocx start' under systemd or your process supervisor.");
+  const ops = platformOps();
+  if (!ops) {
+    console.error("ocx service supports macOS (launchd), Windows (Task Scheduler), and Linux (systemd).");
     process.exit(1);
   }
   switch (sub) {
     case "install":
-      mac ? installLaunchd() : installWindows();
+      ops.install();
       console.log("✅ opencodex service installed + started (auto-starts on login, auto-restarts on crash).");
+      if (process.platform === "linux") console.log("   For auto-start on boot: loginctl enable-linger $USER");
       break;
     case "start":
-      mac ? startLaunchd() : startWindows();
+      ops.start();
       console.log("✅ service started.");
       break;
     case "stop":
-      mac ? stopLaunchd() : stopWindows();
+      ops.stop();
       restoreNativeCodex();
       console.log("✅ service stopped + native Codex restored.");
       break;
     case "status": {
-      const s = mac ? statusLaunchd() : statusWindows();
+      const s = ops.status();
       console.log(s ? `✅ running:\n${s}` : "❌ service not installed/running.");
       break;
     }
     case "uninstall":
     case "remove":
-      mac ? uninstallLaunchd() : uninstallWindows();
+      ops.uninstall();
       restoreNativeCodex();
       console.log("✅ service uninstalled + native Codex restored.");
       break;