Enhance error handling in setupHandler.js for improved robustness

- Replaced assertions with explicit error throwing for missing mainWindow and session.
- Updated protocol handler to return a 400 response for unsupported HTTP requests, enhancing security and clarity.
- Improved internal server error response formatting.

packages/adapter-electron/functions/setupHandler.js

@@ -179,8 +179,13 @@ export async function createRequest(request, session) {
  * @type {import('./setupHandler.d').setupHandler}
  */
 export async function setupHandler(mainWindow) {
-  assert(mainWindow, 'mainWindow is required');
-  assert(mainWindow.webContents.session, 'mainWindow.webContents.session is required');
+  if (!mainWindow) {
+    throw new Error('mainWindow is required for setupHandler');
+  }
+
+  if (!mainWindow.webContents?.session) {
+    throw new Error('mainWindow.webContents.session is required for setupHandler');
+  }
 
   let url = process.env.VITE_DEV_SERVER || Origin
 
@@ -211,7 +216,12 @@ export async function setupHandler(mainWindow) {
       // Handle all http://127.0.0.1 requests
       protocol.handle(Protocol, async (request) => {
 
-        assert(request.url.startsWith(url), 'External HTTP not supported, use HTTPS');
+        if (!request.url.startsWith(url)) {
+          return new Response('External HTTP not supported, use HTTPS instead', {
+            status: 400,
+            headers: { 'content-type': 'text/plain' }
+          });
+        }
 
         const req = await createRequest(request, mainWindow.webContents.session);