This should have been included in PR #30008 (#30009)

Author: rwgk

CMakeLists.txt

@@ -111,8 +111,10 @@ cmake_dependent_option(PYBIND11_FINDPYTHON "Force new FindPython" OFF
 
 # NB: when adding a header don't forget to also add it to setup.py
 set(PYBIND11_HEADERS
+    include/pybind11/detail/abi_platform_id.h
     include/pybind11/detail/class.h
     include/pybind11/detail/common.h
+    include/pybind11/detail/cross_extension_shared_state.h
     include/pybind11/detail/descr.h
     include/pybind11/detail/dynamic_raw_ptr_cast_if_possible.h
     include/pybind11/detail/init.h
@@ -122,6 +124,7 @@ set(PYBIND11_HEADERS
     include/pybind11/detail/smart_holder_type_casters.h
     include/pybind11/detail/type_caster_base.h
     include/pybind11/detail/type_caster_odr_guard.h
+    include/pybind11/detail/type_map.h
     include/pybind11/detail/typeid.h
     include/pybind11/attr.h
     include/pybind11/buffer_info.h