/usr/include/ctemplate/ is in libctemplate-dev 2.3-3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ctemplate/per_expand_data.h
/usr/include/ctemplate/str_ref.h
/usr/include/ctemplate/template.h
/usr/include/ctemplate/template_annotator.h
/usr/include/ctemplate/template_cache.h
/usr/include/ctemplate/template_dictionary.h
/usr/include/ctemplate/template_dictionary_interface.h
/usr/include/ctemplate/template_emitter.h
/usr/include/ctemplate/template_enums.h
/usr/include/ctemplate/template_modifiers.h
/usr/include/ctemplate/template_namelist.h
/usr/include/ctemplate/template_pathops.h
/usr/include/ctemplate/template_string.h