bugfix

backend/src/routes/challenges.js

@@ -185,6 +185,24 @@ router.post('/:id/invite', authMiddleware, asyncHandler(async (req, res) => {
       }
     }
   }
+
+  res.json({ invited: invitedUsers.length });
+}));
+
+// Accept/reject challenge invitation
+router.post('/:id/respond', authMiddleware, asyncHandler(async (req, res) => {
+  const challengeId = req.params.id;
+  const { status } = req.body; // 'accepted' or 'rejected'
+
+  if (!['accepted', 'rejected'].includes(status)) {
+    throw new AppError('Invalid status', 400);
+  }
+
+  await query(
+    'UPDATE challenge_participants SET status = ?, responded_at = NOW() WHERE challenge_id = ? AND user_id = ?',
+    [status, challengeId, req.user.userId]
+  );
+
   // Emit real-time event to challenge participants
   socketEvents.challengeInvitationResponse(challengeId, {
     user_id: req.user.userId,