test: add embedding test for py::enum_ across interpreter restart (gh-5976)

py::enum_ is the primary trigger for gh-5976 because its constructor
creates properties via def_property_static / def_property_readonly_static,
which call process_attributes::init on already-initialized function records.
Yet none of the existing embedding tests used py::enum_ at all.

Add an PYBIND11_EMBEDDED_MODULE with py::enum_ and a test case that imports
it, finalize/reinitializes the interpreter, and re-imports it. This exercises
the def_property_static code path that was fixed in the preceding commit.

Note: on Python 3.14.2 (and likely 3.12+), tp_dealloc_impl is not called
during Py_FinalizeEx for function record PyObjects — they simply leak because
types are effectively immortalized. As a result, this test cannot trigger the
original free()-on-string-literal crash on this Python version. However, it
remains valuable as a regression guard: on Python builds where finalization
does clean up function records (or if CPython changes this behavior), the
test would catch the crash. It also verifies that py::enum_ survives
interpreter restart correctly, which was previously untested.

Made-with: Cursor

Author: rwgk

tests/test_with_catch/test_interpreter.cpp

@@ -84,6 +84,14 @@ PYBIND11_EMBEDDED_MODULE(trampoline_module, m) {
         .def("func", &test_override_cache_helper::func);
 }
 
+enum class SomeEnum { value1, value2 };
+
+PYBIND11_EMBEDDED_MODULE(enum_module, m, py::multiple_interpreters::per_interpreter_gil()) {
+    py::enum_<SomeEnum>(m, "SomeEnum")
+        .value("value1", SomeEnum::value1)
+        .value("value2", SomeEnum::value2);
+}
+
 PYBIND11_EMBEDDED_MODULE(throw_exception, ) { throw std::runtime_error("C++ Error"); }
 
 PYBIND11_EMBEDDED_MODULE(throw_error_already_set, ) {
@@ -343,6 +351,21 @@ TEST_CASE("Restart the interpreter") {
     REQUIRE(py_widget.attr("the_message").cast<std::string>() == "Hello after restart");
 }
 
+TEST_CASE("Enum module survives restart") {
+    // Regression test for gh-5976: py::enum_ uses def_property_static, which
+    // calls process_attributes::init after initialize_generic's strdup loop,
+    // leaving arg names as string literals. Without the fix, destruct() would
+    // call free() on those literals during interpreter finalization.
+    auto enum_mod = py::module_::import("enum_module");
+    REQUIRE(enum_mod.attr("SomeEnum").attr("value1").attr("name").cast<std::string>() == "value1");
+
+    py::finalize_interpreter();
+    py::initialize_interpreter();
+
+    enum_mod = py::module_::import("enum_module");
+    REQUIRE(enum_mod.attr("SomeEnum").attr("value2").attr("name").cast<std::string>() == "value2");
+}
+
 TEST_CASE("Execution frame") {
     // When the interpreter is embedded, there is no execution frame, but `py::exec`
     // should still function by using reasonable globals: `__main__.__dict__`.