fix(worker): return structured internal endpoint errors

tests/test_worker.py

@@ -282,6 +282,46 @@ class TestProcessingWorker(unittest.TestCase):
             self.assertIn("cdr_processed_total", text)
             self.assertIn("cdr_dlq_total", text)
 
+        # Verify unsupported HTTP method returns 501 application/json with structured error
+        req = urllib.request.Request("http://127.0.0.1:18001/metrics", data=b"{}", method="POST")
+        try:
+            urllib.request.urlopen(req)
+            self.fail("Expected HTTPError 501")
+        except urllib.error.HTTPError as exc:
+            self.assertEqual(exc.code, 501)
+            self.assertIn("application/json", exc.headers.get("Content-Type", ""))
+            error_body = json.loads(exc.read().decode("utf-8"))
+            self.assertIn("error", error_body)
+            self.assertIn("detail", error_body)
+
+        # Every error endpoint must use the same structured error contract.
+        try:
+            urllib.request.urlopen("http://127.0.0.1:18001/not-a-route")
+            self.fail("Expected HTTPError 404")
+        except urllib.error.HTTPError as exc:
+            self.assertEqual(exc.code, 404)
+            self.assertIn("application/json", exc.headers.get("Content-Type", ""))
+            error_body = json.loads(exc.read().decode("utf-8"))
+            self.assertEqual(error_body["error"], "not_found")
+            self.assertIn("detail", error_body)
+
+    def test_invalid_unicode_raw_id_routes_to_dlq_safely(self):
+        worker = ProcessingWorker(
+            consumer=self.consumer,
+            dlq_producer=self.dlq_producer,
+            clickhouse=self.clickhouse,
+            batch_size=10,
+            internal_server=self.internal_server,
+        )
+        payload_bytes = b'{"raw_id": "\\ud800", "device_id": "1", "caller_num": "+19875551234", "svc": "4G_DATA", "up_bytes": 10, "down_bytes": 20, "rat": 6, "lac": "1", "ci": "2", "epoch_start": 100, "epoch_end": 200}'
+        msg = MockKafkaMessage(payload_bytes)
+        worker.process_single_message(msg)
+
+        self.assertEqual(len(self.dlq_producer.messages), 1)
+        self.assertIsNone(self.dlq_producer.messages[0]["key"])
+        dlq_data = json.loads(self.dlq_producer.messages[0]["value"].decode("utf-8"))
+        self.assertEqual(dlq_data["failure_reason"], "normalization_error")
+
 
 if __name__ == "__main__":
     unittest.main()