Fall back to next port on EADDRINUSE; show dialog and update tray URL

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

desktop-client/index.js

@@ -1,4 +1,4 @@
-const { app, BrowserWindow, ipcMain } = require('electron');
+const { app, BrowserWindow, ipcMain, dialog } = require('electron');
 const path = require('path');
 const { startServer } = require('./server');
 const { createTray } = require('./tray');
@@ -40,6 +40,17 @@ async function createWindow() {
 app.whenReady().then(async () => {
   serverHandle = await startServer({ port: PORT, overlayDir: OVERLAY_DIR });
 
+  if (serverHandle.port !== PORT) {
+    const actual = serverHandle.port;
+    await dialog.showMessageBox({
+      type: 'info',
+      title: 'Port in use',
+      message: `Port ${PORT} was in use; using ${actual} instead.`,
+      detail: `If you have an OBS browser source pointed at this app, update it to http://localhost:${actual}/`,
+      buttons: ['OK'],
+    });
+  }
+
   ipcMain.on('wtm:state', (_event, payload) => {
     const next = serverHandle.setState(payload || { isPlaying: false });
     if (tray) tray.update({ title: next.title, artist: next.artist });
@@ -48,7 +59,7 @@ app.whenReady().then(async () => {
   await createWindow();
 
   tray = createTray({
-    port: PORT,
+    port: serverHandle.port,
     onShow: () => {
       if (!mainWindow) return;
       if (mainWindow.isMinimized()) mainWindow.restore();