given flaky --parallel FT pipeline fails, new fix in core.runner, incl. _Py313SafeRemoteTestRunner, so that errors bubbling up don't read as generic TypeError: cannot pickle 'traceback' object

src/core/runner.py

@@ -1,8 +1,43 @@
+import pickle
 import time
-from django.test.runner import DiscoverRunner
+from django.test.runner import DiscoverRunner, ParallelTestSuite, RemoteTestRunner
+
+
+class _Py313SafeRemoteTestRunner(RemoteTestRunner):
+    """Prevents Python 3.13 'cannot pickle traceback' crash in parallel workers.
+
+    In Python 3.13, traceback objects are not picklable. Django's parallel
+    runner tries to pickle test errors to pass them back to the main process.
+    When a Selenium test crashes the browser, the resulting exception traceback
+    fails to pickle, aborting the entire parallel run with a confusing TypeError.
+
+    Fix: strip the traceback (replace with None) before it reaches pickle.
+    Error type and message are preserved; only the traceback is lost in transit.
+    """
+
+    @staticmethod
+    def _strip_tb_if_needed(err):
+        exc_type, exc_value, exc_tb = err
+        try:
+            pickle.dumps((exc_type, exc_value, exc_tb))
+        except (TypeError, AttributeError):
+            return (exc_type, exc_value, None)
+        return err
+
+    def addError(self, test, err):
+        super().addError(test, self._strip_tb_if_needed(err))
+
+    def addFailure(self, test, err):
+        super().addFailure(test, self._strip_tb_if_needed(err))
+
+
+class _SafeParallelTestSuite(ParallelTestSuite):
+    runner_class = _Py313SafeRemoteTestRunner
 
 
 class RobustCompressorTestRunner(DiscoverRunner):
+    parallel_test_suite = _SafeParallelTestSuite
+
     def setup_test_environment(self, **kwargs):
         super().setup_test_environment(**kwargs)
         from compressor.storage import CompressorFileStorage