fix: auto-terminate stale bot instances to prevent port conflicts

- Added execSync import for child_process
- Modified acquirePidfile() to send SIGTERM to old instances
- Waits up to 2.5s for graceful shutdown with checks every 500ms
- Prevents continuous restart loop when old PID holds port 3001
- Bot now self-heals on restart instead of crashing

src/bot/index.js

@@ -6,6 +6,7 @@ import { createServer } from 'http';
 import { WebSocketServer } from 'ws';
 import fs from 'fs';
 import path from 'path';
+import { execSync } from 'child_process';
 import { logger } from '../utils/logger.js';
 import { checkEnv } from '../utils/env.js';
 import { getRTK } from '../utils/rtk.js';
@@ -37,16 +38,33 @@ function acquirePidfile() {
     if (fs.existsSync(PIDFILE)) {
       const oldPid = parseInt(fs.readFileSync(PIDFILE, 'utf8').trim());
       // Check if old process is still alive
-      try { process.kill(oldPid, 0); 
-        // Same PID or different process - just log warning, don't kill
+      try { process.kill(oldPid, 0);
+        // Old process is still running - kill it to prevent port conflicts
         if (oldPid !== process.pid) {
-          logger.warn(`⚠ Another zCode instance (PID ${oldPid}) is running — keeping this instance (PID ${process.pid})`);
+          logger.warn(`⚠ Another zCode instance (PID ${oldPid}) detected — terminating to prevent port conflict`);
+          try {
+            process.kill(oldPid, 'SIGTERM');
+            logger.info(`  ✓ Sent SIGTERM to PID ${oldPid}`);
+            // Give it time to shut down gracefully
+            for (let i = 0; i < 5; i++) {
+              try { process.kill(oldPid, 0); }
+              catch { break; } // Process is dead
+              if (i < 4) {
+                // Sleep 500ms between checks
+                execSync('sleep 0.5', { stdio: 'ignore' });
+              }
+            }
+          } catch (e) {
+            logger.warn(`  Failed to kill old PID ${oldPid}: ${e.message}`);
+          }
         } else {
           logger.info(`✓ Pidfile already acquired by this instance (PID ${process.pid})`);
         }
-        // Don't kill - just continue with current process
-        return;
-      } catch { /* old PID dead, safe to acquire */ }
+        // Continue - old process should be dead now
+      } catch {
+        // Old PID dead, safe to acquire
+        logger.info(`  Old PID ${oldPid} is no longer running`);
+      }
     }
     fs.writeFileSync(PIDFILE, process.pid.toString());
     logger.info(`✓ Pidfile acquired: ${PIDFILE} (PID ${process.pid})`);