feat(updater): electron-updater wiring + IPC bridge

electron-updater integration so users get fixes automatically:
  - new dependency electron-updater@^6.6.2 in package.json
  - electron-builder.config.js publishes to GitHub releases
    (owner: concreteinfo, repo: markdownconverter)
  - new src/main/auto-updater.js wraps autoUpdater: wires the six
    lifecycle events to a 'updates:status' IPC channel, exposes
    check() and install() helpers, dev-gates via isDev(), and
    swallows the 'missing app-update.yml' error that dev runs hit
  - main.js: ensureAutoUpdater() forwards status to the renderer
    via mainWindow.webContents.send; ipcMain handlers for
    'updates:check' (invoke) and 'updates:install' (invoke)
  - preload.js: 'updates:check' / 'updates:install' added to
    ALLOWED_SEND_CHANNELS; 'updates:status' added to receive
    channels; electronAPI.updates.{check, install, onStatus}
    exposed

7 new tests cover event registration, dev-gate behaviour,
'not-available' fallback for missing app-update.yml, typed event
payloads, error forwarding, and install() quitAndInstall.

Amit Haridas

src/main.js

@@ -11,6 +11,7 @@ const VideoOperations = require('./main/VideoOperations');
 const { collectFilesByExtension } = require('./main/collectFilesByExtension');
 const { listWorkspaceFiles } = require('./quick-switcher/workspace-file-lister');
 const { completeStream } = require('./main/AiProviders');
+const { setupAutoUpdater } = require('./main/auto-updater');
 const { runPDFBatchOperation } = require('./main/PDFBatchOperations');
 const GitOperations = require('./main/GitOperations');
 const PandocArgs = require('./main/PandocArgs');
@@ -4948,6 +4949,29 @@ ipcMain.on('ai-assist-stream:cancel', (_event, { requestId } = {}) => {
   if (entry) entry.abort();
 });
 
+// Auto-update wiring (v4.13.0). Surfaces status to the renderer and
+// exposes check-now / install-now IPC channels. Lazy-instantiated so a
+// missing app-update.yml in dev doesn't blow up startup.
+let autoUpdaterCtl = null;
+function ensureAutoUpdater() {
+  if (autoUpdaterCtl) return autoUpdaterCtl;
+  autoUpdaterCtl = setupAutoUpdater({
+    send: (channel, payload) => {
+      if (mainWindow && !mainWindow.isDestroyed()) {
+        mainWindow.webContents.send(channel, payload);
+      }
+    },
+    isDev: () => process.env.NODE_ENV === 'development' || !!process.env.ELECTRON_DEV,
+  });
+  return autoUpdaterCtl;
+}
+ipcMain.handle('updates:check', async () => {
+  return ensureAutoUpdater().check();
+});
+ipcMain.handle('updates:install', () => {
+  ensureAutoUpdater().install();
+});
+
 // Plugins (loaded in the renderer) report the export formats they've
 // registered; rebuild the Export menu so they show up as entries.
 // createMenu() is idempotent and already re-invoked elsewhere (e.g. after

src/main/auto-updater.js

@@ -0,0 +1,75 @@
+/**
+ * Auto-updater wiring for electron-updater.
+ *
+ * Wraps electron-updater's autoUpdater so the main process has one place
+ * to:
+ *   - start a check on app launch
+ *   - forward events to the renderer over 'updates:status' IPC
+ *   - accept "install now" / "check now" requests from the renderer
+ *
+ * Safe to call in dev: when no app-update.yml is packaged (which is the
+ * case for `npm start` / electron .), electron-updater surfaces an
+ * "app-update.yml not found" error which we swallow and log. The renderer
+ * still gets a `not-available` event so the UI can show "you're up to
+ * date" instead of a spinning indicator that never resolves.
+ *
+ * @module auto-updater
+ */
+
+/**
+ * @param {object} deps
+ * @param {(channel:string, payload?:any) => void} deps.send - forwards
+ *   status events to the BrowserWindow's webContents
+ * @param {() => boolean} [deps.isDev] - dev gate (skip check in dev)
+ */
+function setupAutoUpdater({ send, isDev }) {
+  // Lazy-load — electron-updater touches `app` at import time, which fails
+  // in test environments where the app isn't bootstrapped.
+  const { autoUpdater } = require('electron-updater');
+
+  autoUpdater.autoDownload = true;
+  autoUpdater.autoInstallOnAppQuit = true;
+
+  // Forward every event to the renderer with a typed payload.
+  autoUpdater.on('checking-for-update', () => send('updates:status', { state: 'checking' }));
+  autoUpdater.on('update-available', (info) =>
+    send('updates:status', { state: 'available', version: info?.version })
+  );
+  autoUpdater.on('update-not-available', (info) =>
+    send('updates:status', { state: 'not-available', version: info?.version })
+  );
+  autoUpdater.on('download-progress', (p) =>
+    send('updates:status', { state: 'downloading', percent: Math.round(p.percent || 0) })
+  );
+  autoUpdater.on('update-downloaded', (info) =>
+    send('updates:status', { state: 'downloaded', version: info?.version })
+  );
+  autoUpdater.on('error', (err) =>
+    send('updates:status', {
+      state: 'error',
+      message: err && err.message ? err.message : 'Update check failed.',
+    })
+  );
+
+  function check() {
+    if (typeof isDev === 'function' && isDev()) return Promise.resolve(null);
+    return autoUpdater.checkForUpdates().catch((err) => {
+      // Dev runs surface "app-update.yml not found" — treat that as benign.
+      const msg = err && err.message ? err.message : String(err);
+      if (msg.includes('app-update.yml') || msg.includes('Cannot find')) {
+        send('updates:status', { state: 'not-available' });
+        return null;
+      }
+      send('updates:status', { state: 'error', message: msg });
+      return null;
+    });
+  }
+
+  function install() {
+    autoUpdater.quitAndInstall();
+  }
+
+  return { check, install };
+}
+
+module.exports = { setupAutoUpdater };

src/preload.js

@@ -48,6 +48,10 @@ const ALLOWED_SEND_CHANNELS = [
   'ai-assist-stream:start',
   'ai-assist-stream:cancel',
 
+  // v4.13.0 — auto-update (electron-updater)
+  'updates:check',
+  'updates:install',
+
   // Batch conversion
   'batch-convert',
   'select-folder',
@@ -338,6 +342,9 @@ const ALLOWED_RECEIVE_CHANNELS = [
   // v4.13.0 — quick-switcher overlay trigger
   'show-quick-switcher',
 
+  // v4.13.0 — auto-update status events from main
+  'updates:status',
+
   // Plugin export formats
   'run-plugin-export-format',
 ];
@@ -581,6 +588,15 @@ contextBridge.exposeInMainWorld('electronAPI', {
     onError: (cb) => ipcRenderer.on('ai-assist-stream:error', (_e, p) => cb(p)),
   },
 
+  // v4.13.0 — auto-update controls. Check-now asks main to poll
+  // GitHub releases; install-now triggers quitAndInstall. Status events
+  // arrive via the generic on('updates:status', cb).
+  updates: {
+    check: () => ipcRenderer.invoke('updates:check'),
+    install: () => ipcRenderer.invoke('updates:install'),
+    onStatus: (cb) => ipcRenderer.on('updates:status', (_e, p) => cb(p)),
+  },
+
   getAppVersion: () => ipcRenderer.invoke('get-app-version'),
 });