feat: lockfile to prevent parallel runs + AI keywords lib

lib/lock.mjs

@@ -0,0 +1,34 @@
+/**
+ * lock.mjs — Simple PID-based lockfile to prevent parallel runs
+ */
+import { existsSync, readFileSync, writeFileSync, unlinkSync } from 'fs';
+import { resolve } from 'path';
+
+export function acquireLock(name, dataDir) {
+  const lockFile = resolve(dataDir, `${name}.lock`);
+
+  if (existsSync(lockFile)) {
+    const pid = parseInt(readFileSync(lockFile, 'utf8').trim(), 10);
+    // Check if that process is still alive
+    try {
+      process.kill(pid, 0); // signal 0 = check existence only
+      console.error(`⚠️  ${name} already running (PID ${pid}). Exiting.`);
+      process.exit(0);
+    } catch {
+      // Stale lock — process is gone, safe to continue
+      console.warn(`🔓 Stale lock found (PID ${pid}), clearing.`);
+    }
+  }
+
+  writeFileSync(lockFile, String(process.pid));
+
+  // Release lock on exit (normal or crash)
+  const release = () => {
+    try { unlinkSync(lockFile); } catch {}
+  };
+  process.on('exit', release);
+  process.on('SIGINT', () => { release(); process.exit(130); });
+  process.on('SIGTERM', () => { release(); process.exit(143); });
+
+  return release;
+}