step 10.4: done

src/routes/auth.js

@@ -51,6 +51,7 @@ async function handleRegister(req, res) {
   req.session.regenerate((err) => {
     if (err) throw new AppError('INTERNAL_ERROR', 'Session regeneration failed.', 500);
     req.session.userId = user.id;
+    req.session.username = user.username;
     res.status(201).json({ ok: true, data: { user: { id: user.id, username: user.username } } });
   });
 }