Cross-interpreter memory leak in _xidata_release when originating interpreter is destroyed

Bug report

Bug description:

Bug report

Bug summary
There is a known memory leak in Python/crossinterp.c related to the teardown of sub-interpreters when they share data.

When a sub-interpreter packages data into _PyXIData_t and passes it to a receiving interpreter, the receiver is expected to call _PyXIData_Release to free it. However, if the originating interpreter is destroyed before the receiver calls release, the original interpreter's memory context is lost.

In _xidata_release (Python/crossinterp.c around line 1049), the code correctly identifies this state:

    PyInterpreterState *interp = _PyInterpreterState_LookUpID(
                                        _PyXIData_INTERPID(xidata));
    if (interp == NULL) {
        // The interpreter was already destroyed.
        // This function shouldn't have been called.
        // XXX Someone leaked some memory...

Because the originating interpreter is gone, Python intentionally leaks xidata->obj to avoid a use-after-free segfault.

Proposed Solution Architecture
To resolve this without crashing, we would need to track cross-interpreter data at the interpreter level:

1. Modify PyInterpreterState to include a thread-safe registry tracking all active _PyXIData_t instances created by that interpreter.
2. Register instances during _PyCode_GetXIData and deregister them during _xidata_release.
3. Modify Py_EndInterpreter teardown to check this registry. If outstanding shared data exists, the shutting-down interpreter must either block until it is released, or forcefully invalidate/free the shared data (using an is_invalidated flag) before tearing down its own obmalloc state.

I'm opening this issue to get feedback on the proposed architecture before starting a Pull Request.

CPython versions tested on:
main branch

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-153745

Start with Python/crossinterp.c around _xidata_release, then trace _PyCode_GetXIData and the Py_EndInterpreter teardown path. Review the linked gh-153745 work before proceeding, since this issue asks for architectural feedback and does not define a settled implementation or completion test.