AssertionError in test.test_multiprocessing_spawn.test_processes.WithProcessesTestProcess.test_interrupt

Bug report

Bug description:

I try to build Python 3.14.0b1 on Fedora Linux 42, 41, 40, the test has failed so far (the list is incomplete) for debug and freethreading-debug builds, on x86_64, i686, aarch64 arches. Traceback is in all cases similar with the difference of pipe_handle argument value.

Re-running test.test_multiprocessing_spawn.test_processes in verbose mode (matching: test_interrupt)
test_interrupt (test.test_multiprocessing_spawn.test_processes.WithProcessesTestProcess.test_interrupt) ... Traceback (most recent call last):
  File "<string>", line 1, in <module>
    from multiprocessing.spawn import spawn_main; spawn_main(tracker_fd=5, pipe_handle=7)
                                                  ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/multiprocessing/spawn.py", line 122, in spawn_main
    exitcode = _main(fd, parent_sentinel)
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/multiprocessing/spawn.py", line 131, in _main
    prepare(preparation_data)
    ~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/multiprocessing/spawn.py", line 244, in prepare
    _fixup_main_from_name(data['init_main_from_name'])
    ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/multiprocessing/spawn.py", line 268, in _fixup_main_from_name
    main_content = runpy.run_module(mod_name,
                                    run_name="__mp_main__",
                                    alter_sys=True)
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/runpy.py", line 226, in run_module
    return _run_module_code(code, init_globals, run_name, mod_spec)
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/runpy.py", line 98, in _run_module_code
    _run_code(code, mod_globals, init_globals,
    ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
              mod_name, mod_spec, pkg_name, script_name)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/runpy.py", line 88, in _run_code
    exec(code, run_globals)
    ~~~~^^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/test/libregrtest/worker.py", line 8, in <module>
    from .setup import setup_process, setup_test_dir
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/test/libregrtest/setup.py", line 12, in <module>
    from .runtests import RunTests
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/test/libregrtest/runtests.py", line 194, in <module>
    @dataclasses.dataclass(slots=True, frozen=True)
     ~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/dataclasses.py", line 1362, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
                          frozen, match_args, kw_only, slots,
                          weakref_slot)
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/dataclasses.py", line 1163, in _process_class
    func_builder.add_fns_to_class(cls)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/dataclasses.py", line 507, in add_fns_to_class
    fns = ns['__create_fn__'](**self.locals)
  File "<string>", line 28, in __create_fn__
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/reprlib.py", line 32, in decorating_function
    wrapper.__type_params__ = getattr(user_function, '__type_params__', ())
                              ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
KeyboardInterrupt
FAIL
======================================================================
FAIL: test_interrupt (test.test_multiprocessing_spawn.test_processes.WithProcessesTestProcess.test_interrupt)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/builddir/build/BUILD/Python-3.14.0b1/Lib/test/_test_multiprocessing.py", line 578, in test_interrupt
    self.assertEqual(exitcode, 1)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^
AssertionError: -2 != 1

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Start with test.test_multiprocessing_spawn.test_processes.WithProcessesTestProcess.test_interrupt in Lib/test/_test_multiprocessing.py and reproduce it on the affected Linux debug or freethreading-debug build. Trace the spawned process through Lib/multiprocessing/spawn.py and the dataclass path in Lib/test/libregrtest/runtests.py and Lib/reprlib.py; done means the test completes with the intended exit code across the reported configurations.