Reclaim stale script lock after crash (v1.3.1)

The single-tab lock was only released in beforeunload, so a browser
crash or power-cut left the localStorage key behind and the script
exited on every subsequent load until site data was cleared.

Treat a lock not refreshed within 90s as dead and take it over, and
add a 30s heartbeat so a live instance keeps its lock fresh.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cams.user.js

@@ -1,7 +1,7 @@
 // ==UserScript==
 // @name         cams
 // @namespace    http://tampermonkey.net/
-// @version      1.3.0
+// @version      1.3.1
 // @description  Set maxDockedCamsForUser, keep-alive, and multi-poke
 // @author       You
 // @match        https://chat.fabswingers.com/*
@@ -223,18 +223,37 @@
         localStorage.setItem(KEEPALIVE_SETTINGS_KEY, JSON.stringify(keepAliveSettings));
     }
 
-    // Try to acquire lock
+    // Try to acquire lock.
-    const lockValue = Date.now().toString();
+    // The lock value is a timestamp that a live instance refreshes on a heartbeat.
+    // If a crash / power-cut kills the tab, beforeunload never fires and the key is
+    // left behind; a new load treats a lock older than LOCK_STALE_MS as dead and
+    // takes over, instead of exiting forever (which required clearing site data).
+    const LOCK_STALE_MS = 90 * 1000;      // reclaim a lock not refreshed within 90s
+    const LOCK_HEARTBEAT_MS = 30 * 1000;  // refresh our lock every 30s while alive
+    let ourLockValue = Date.now().toString();
 
-    if (localStorage.getItem(LOCK_KEY)) {
+    const existingLock = localStorage.getItem(LOCK_KEY);
+    if (existingLock) {
+        const lockAge = Date.now() - parseInt(existingLock, 10);
+        if (isNaN(lockAge) || lockAge < LOCK_STALE_MS) {
             console.log('MaxDockedCams: Another instance already running, exiting');
             return;
         }
+        console.log(`MaxDockedCams: Reclaiming stale lock (${Math.round(lockAge / 1000)}s old)`);
+    }
 
-    localStorage.setItem(LOCK_KEY, lockValue);
+    localStorage.setItem(LOCK_KEY, ourLockValue);
+
+    // Keep our lock fresh so a live instance is never mistaken for a crashed one.
+    setInterval(function() {
+        if (localStorage.getItem(LOCK_KEY) === ourLockValue) {
+            ourLockValue = Date.now().toString();
+            localStorage.setItem(LOCK_KEY, ourLockValue);
+        }
+    }, LOCK_HEARTBEAT_MS);
 
     window.addEventListener('beforeunload', function() {
-        if (localStorage.getItem(LOCK_KEY) === lockValue) {
+        if (localStorage.getItem(LOCK_KEY) === ourLockValue) {
             localStorage.removeItem(LOCK_KEY);
         }
     });

meta.js

@@ -1,7 +1,7 @@
 // ==UserScript==
 // @name         cams
 // @namespace    http://tampermonkey.net/
-// @version      1.3.0
+// @version      1.3.1
 // @description  Set maxDockedCamsForUser, keep-alive, and multi-poke
 // @author       You
 // @match        https://chat.fabswingers.com/*