fix: graceful shutdown — write last-run file on SIGTERM, show interrupted state in status

lib/lock.mjs

@@ -26,9 +26,21 @@ export function acquireLock(name, dataDir) {
   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;
+  // Graceful shutdown — call registered cleanup before exiting
+  const shutdownHandlers = [];
+  const shutdown = (code) => async () => {
+    console.log(`\n⚠️  ${name}: signal received, shutting down gracefully...`);
+    for (const fn of shutdownHandlers) {
+      try { await fn(); } catch {}
+    }
+    release();
+    process.exit(code);
+  };
+
+  process.on('exit', release);
+  process.on('SIGINT', shutdown(130));
+  process.on('SIGTERM', shutdown(143));
+
+  return { release, onShutdown: (fn) => shutdownHandlers.push(fn) };
 }