test leaving challange invited to

backend/src/routes/challenges.js

@@ -213,6 +213,43 @@ router.post('/:id/respond', authMiddleware, asyncHandler(async (req, res) => {
   res.json({ status });
 }));
 
+// Leave a challenge (participants only, not creator)
+router.post('/:id/leave', authMiddleware, asyncHandler(async (req, res) => {
+  const challengeId = req.params.id;
+
+  // Get challenge to verify it exists and user is not creator
+  const challenges = await query(
+    'SELECT * FROM challenges WHERE id = ?',
+    [challengeId]
+  );
+
+  if (challenges.length === 0) {
+    throw new AppError('Challenge not found', 404);
+  }
+
+  const challenge = challenges[0];
+
+  if (challenge.created_by === req.user.userId) {
+    throw new AppError('Challenge creator cannot leave. Delete the challenge instead.', 403);
+  }
+
+  // Check if user is a participant
+  const participation = await query(
+    'SELECT * FROM challenge_participants WHERE challenge_id = ? AND user_id = ?',
+    [challengeId, req.user.userId]
+  );
+
+  if (participation.length === 0) {
+    throw new AppError('You are not a participant of this challenge', 404);
+  }
+
+  // Delete user's participation and predictions
+  await query('DELETE FROM predictions WHERE challenge_id = ? AND user_id = ?', [challengeId, req.user.userId]);
+  await query('DELETE FROM challenge_participants WHERE challenge_id = ? AND user_id = ?', [challengeId, req.user.userId]);
+
+  res.json({ success: true, message: 'Left challenge successfully' });
+}));
+
 // Delete a challenge (only creator can delete)
 router.delete('/:id', authMiddleware, asyncHandler(async (req, res) => {
   const challengeId = req.params.id;