/usr/include/osmium/io/detail/ is in libosmium2-dev 2.11.4-1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/osmium/io/detail/debug_output_format.hpp
/usr/include/osmium/io/detail/input_format.hpp
/usr/include/osmium/io/detail/o5m_input_format.hpp
/usr/include/osmium/io/detail/opl_input_format.hpp
/usr/include/osmium/io/detail/opl_output_format.hpp
/usr/include/osmium/io/detail/opl_parser_functions.hpp
/usr/include/osmium/io/detail/output_format.hpp
/usr/include/osmium/io/detail/pbf.hpp
/usr/include/osmium/io/detail/pbf_decoder.hpp
/usr/include/osmium/io/detail/pbf_input_format.hpp
/usr/include/osmium/io/detail/pbf_output_format.hpp
/usr/include/osmium/io/detail/protobuf_tags.hpp
/usr/include/osmium/io/detail/queue_util.hpp
/usr/include/osmium/io/detail/read_thread.hpp
/usr/include/osmium/io/detail/read_write.hpp
/usr/include/osmium/io/detail/string_table.hpp
/usr/include/osmium/io/detail/string_util.hpp
/usr/include/osmium/io/detail/write_thread.hpp
/usr/include/osmium/io/detail/xml_input_format.hpp
/usr/include/osmium/io/detail/xml_output_format.hpp
/usr/include/osmium/io/detail/zlib.hpp