🐛 fix: folder monitor re-detect deleted files, atomic sync save

- Folder monitor: clear _seenFiles entry on file unlink so re-added
  files (e.g. re-encoded) are detected again
- Sync IPC save (beforeunload): use atomic write pattern with backup
  (.bak) creation, matching the async _atomicWrite behavior

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lib/folder-monitor.js

@@ -35,6 +35,11 @@ class FolderMonitor extends EventEmitter {
 
     this._watcher = chokidar.watch(folderPath, watchOptions);
     this._watcher.on('add', (filePath) => this._onNewFile(filePath));
+    this._watcher.on('unlink', (filePath) => {
+      // Allow re-added files (e.g. re-encoded) to be detected again
+      const normalized = filePath.replace(/\\/g, '/').toLowerCase();
+      this._seenFiles.delete(normalized);
+    });
     this._watcher.on('error', (err) => this.emit('error', err));
   }
 

main.js

@@ -883,11 +883,22 @@ ipcMain.handle('save-global-settings', async (_event, globalSettings) => {
 });
 
 // Synchronous save for beforeunload — blocks renderer until write completes
+// Uses atomic write pattern (tmp + backup + rename) to prevent corruption
 ipcMain.on('save-global-settings-sync', (event, globalSettings) => {
   try {
     const current = configStore.load();
     current.globalSettings = globalSettings;
-    fs.writeFileSync(configStore.filePath, JSON.stringify(current, null, 2));
+    const data = JSON.stringify(current, null, 2);
+    const tmpPath = configStore.filePath + '.tmp';
+    const backupPath = configStore.filePath + '.bak';
+    fs.writeFileSync(tmpPath, data, 'utf-8');
+    if (fs.existsSync(configStore.filePath)) {
+      const existing = fs.readFileSync(configStore.filePath, 'utf-8');
+      if (existing && existing.trim().length > 2) {
+        fs.writeFileSync(backupPath, existing, 'utf-8');
+      }
+    }
+    fs.renameSync(tmpPath, configStore.filePath);
   } catch {}
   event.returnValue = true;
 });