fix: Major bug cleanup pass 1

server/src/routes/users.ts

@@ -10,6 +10,7 @@ import {
 import { hashPasswordForStorage, verifyPassword } from '../services/password-auth.service';
 import { issueSessionToken, revokeSessionToken } from '../services/session-auth.service';
 import { getAuthenticatedUserId, requireAuth } from '../middleware/require-auth';
+import { isDuplicateUsernameError } from './user-registration.rules';
 
 const router = Router();
 
@@ -46,7 +47,16 @@ router.post('/register', async (req, res) => {
     createdAt: Date.now()
   };
 
-  await registerUser(user);
+  try {
+    await registerUser(user);
+  } catch (error) {
+    if (isDuplicateUsernameError(error)) {
+      return res.status(409).json({ error: 'Username taken' });
+    }
+
+    throw error;
+  }
+
   const session = await issueSessionToken(user.id);
 
   res.status(201).json(buildAuthResponse(user, session.token, session.expiresAt));