Add the repro test into test_queues.py.

Author: note35

Lib/test/test_interpreters/test_queues.py

@@ -8,6 +8,7 @@
 # Raise SkipTest if subinterpreters not supported.
 _queues = import_helper.import_module('_interpqueues')
 from concurrent import interpreters
+from concurrent.futures import InterpreterPoolExecutor
 from concurrent.interpreters import _queues as queues, _crossinterp
 from .utils import _run_output, TestBase as _TestBase
 
@@ -93,6 +94,14 @@ def test_bind_release(self):
             with self.assertRaises(queues.QueueError):
                 _queues.release(qid)
 
+    def test_interpreter_pool_executor_after_reload(self):
+        # Regression test for gh-142414 (KeyError in serialize_unbound).
+        importlib.reload(queues)
+        code = "import struct"
+        with InterpreterPoolExecutor(max_workers=1) as executor:
+            results = executor.map(exec, [code] * 1)
+            self.assertEqual(list(results), [None] * 1)
+
 
 class QueueTests(TestBase):
 

Misc/NEWS.d/next/Library/2025-12-10-15-27-58.gh-issue-142414.zTHgP-.rst

@@ -1 +1 @@
-Unified the UNBOUND constant in the internal implementation of Lib/concurrent/interpreters.
+Fix spurious KeyError when concurrent.interpreters is reloaded after import.