fix: pidfile lock + port conflict guard + systemd ready

- Pidfile lock prevents duplicate instances (auto-kills stale PIDs)
- EADDRINUSE retry: kills port hog, retries up to 3x with 1.5s delay
- releasePidfile() on graceful shutdown
- Added fs/path imports needed by pidfile utilities

src/bot/index.js

@@ -4,6 +4,8 @@ import { sequentialize } from '@grammyjs/runner';
 import express from 'express';
 import { createServer } from 'http';
 import { WebSocketServer } from 'ws';
+import fs from 'fs';
+import path from 'path';
 import { logger } from '../utils/logger.js';
 import { checkEnv } from '../utils/env.js';
 import { getRTK } from '../utils/rtk.js';
@@ -13,6 +15,36 @@ import { sendFormatted, splitMessage, escapeMarkdown, sendStreamingMessage, Stre
 import { withSelfCorrection } from './self-correction.js';
 import { getMemory, getConversation } from './memory.js';
 
+// ── Pidfile lock: prevent duplicate instances ──
+const PIDFILE = path.join(process.env.HOME || '/tmp', '.zcode-bot.pid');
+function acquirePidfile() {
+  try {
+    if (fs.existsSync(PIDFILE)) {
+      const oldPid = parseInt(fs.readFileSync(PIDFILE, 'utf8').trim());
+      // Check if old process is still alive
+      try { process.kill(oldPid, 0); 
+        logger.warn(`⚠ Another zCode instance (PID ${oldPid}) is running — killing stale process`);
+        process.kill(oldPid, 'SIGTERM');
+        // Wait briefly for cleanup
+        const deadline = Date.now() + 5000;
+        while (Date.now() < deadline) {
+          try { process.kill(oldPid, 0); } catch { break; }
+          Atomics.wait(new Int32Array(new SharedArrayBuffer(4)), 0, 0, 200);
+        }
+        // Force kill if still alive
+        try { process.kill(oldPid, 0); process.kill(oldPid, 'SIGKILL'); } catch {}
+      } catch { /* old PID dead, safe */ }
+    }
+    fs.writeFileSync(PIDFILE, process.pid.toString());
+    logger.info(`✓ Pidfile acquired: ${PIDFILE} (PID ${process.pid})`);
+  } catch (e) {
+    logger.error(`Pidfile error: ${e.message}`);
+  }
+}
+function releasePidfile() {
+  try { if (fs.existsSync(PIDFILE)) fs.unlinkSync(PIDFILE); } catch {}
+}
+
 function buildSessionKey(chatId, threadId) {
   return threadId ? `${chatId}:${threadId}` : String(chatId);
 }
@@ -761,11 +793,14 @@ export async function initBot(config, api, tools, skills, agents) {
   const shutdown = async (signal) => {
     logger.info(`🛑 Shutting down (${signal})...`);
     await conversation.flush();
+    releasePidfile();
     process.exit(0);
   };
   process.on('SIGINT', () => shutdown('SIGINT'));
   process.on('SIGTERM', () => shutdown('SIGTERM'));
 
+  acquirePidfile();
+
   // ── Express + WebSocket server (keep for webhook compatibility) ──
   const app = express();
   app.use(express.json());
@@ -818,10 +853,39 @@ export async function initBot(config, api, tools, skills, agents) {
   });
 
   const PORT = process.env.ZCODE_PORT || 3000;
-  httpServer.listen(PORT, () => {
-    logger.info(`✓ HTTP on :${PORT} · WS ready · grammy bot online`);
-    logger.info(`✓ ${svc.tools.length} tools · ${svc.skills.length} skills · ${svc.agents.length} agents`);
+  // ── Port conflict guard: retry with cleanup ──
+  let listenAttempts = 0;
+  const MAX_LISTEN_ATTEMPTS = 3;
+  function tryListen() {
+    httpServer.listen(PORT, () => {
+      logger.info(`✓ HTTP on :${PORT} · WS ready · grammy bot online`);
+      logger.info(`✓ ${svc.tools.length} tools · ${svc.skills.length} skills · ${svc.agents.length} agents`);
+    });
+  }
+  httpServer.on('error', (err) => {
+    if (err.code === 'EADDRINUSE' && listenAttempts < MAX_LISTEN_ATTEMPTS) {
+      listenAttempts++;
+      logger.warn(`⚠ Port ${PORT} in use (attempt ${listenAttempts}/${MAX_LISTEN_ATTEMPTS}) — killing stale process`);
+      // Find and kill process on that port
+      try {
+        const { execSync } = require('child_process');
+        const out = execSync(`fuser ${PORT}/tcp 2>/dev/null`, { encoding: 'utf8' }).trim();
+        if (out) {
+          out.split(/\s+/).forEach(pid => {
+            try {
+              const p = parseInt(pid);
+              if (p !== process.pid) { process.kill(p, 'SIGTERM'); logger.warn(`  Killed PID ${p}`); }
+            } catch {}
+          });
+        }
+      } catch {}
+      setTimeout(tryListen, 1500);
+    } else {
+      logger.error(`❌ Failed to bind port ${PORT}: ${err.message}`);
+      process.exit(1);
+    }
   });
+  tryListen();
 
   // Set webhook
   const wu = process.env.ZCODE_WEBHOOK_URL;