Merge pull request #939 from charlesedeh021-cell/fix/error-handler-headers-sent-819

Guard error handler after headers are sent

Author: ogazboiz

backend/src/middleware/error.middleware.ts

@@ -14,6 +14,10 @@ export const errorHandler = (
 ) => {
     logger.error('Unhandled error:', err);
 
+    if (res.headersSent) {
+        return next(err);
+    }
+
     // Handle Zod Validation Errors
     if (err instanceof ZodError) {
         return res.status(400).json({

backend/tests/error.middleware.test.ts

@@ -44,4 +44,15 @@ describe('Error Middleware', () => {
     errorHandler(error, req as Request, res as Response, next);
     expect(res.status).toHaveBeenCalledWith(500);
   });
+
+  it('should delegate to next when headers were already sent', () => {
+    const error = new Error('Stream failed after headers');
+    res.headersSent = true;
+
+    errorHandler(error, req as Request, res as Response, next);
+
+    expect(next).toHaveBeenCalledWith(error);
+    expect(res.status).not.toHaveBeenCalled();
+    expect(res.json).not.toHaveBeenCalled();
+  });
 });