/usr/include/net-snmp/agent/ is in libsnmp-dev 5.7.3+dfsg-1.7+deb9u1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/net-snmp/agent/agent_callbacks.h
/usr/include/net-snmp/agent/agent_handler.h
/usr/include/net-snmp/agent/agent_index.h
/usr/include/net-snmp/agent/agent_module_config.h
/usr/include/net-snmp/agent/agent_read_config.h
/usr/include/net-snmp/agent/agent_registry.h
/usr/include/net-snmp/agent/agent_sysORTable.h
/usr/include/net-snmp/agent/agent_trap.h
/usr/include/net-snmp/agent/all_helpers.h
/usr/include/net-snmp/agent/auto_nlist.h
/usr/include/net-snmp/agent/baby_steps.h
/usr/include/net-snmp/agent/bulk_to_next.h
/usr/include/net-snmp/agent/cache_handler.h
/usr/include/net-snmp/agent/debug_handler.h
/usr/include/net-snmp/agent/ds_agent.h
/usr/include/net-snmp/agent/header_complex.h
/usr/include/net-snmp/agent/instance.h
/usr/include/net-snmp/agent/mfd.h
/usr/include/net-snmp/agent/mib_module_config.h
/usr/include/net-snmp/agent/mib_module_includes.h
/usr/include/net-snmp/agent/mib_modules.h
/usr/include/net-snmp/agent/mode_end_call.h
/usr/include/net-snmp/agent/multiplexer.h
/usr/include/net-snmp/agent/net-snmp-agent-includes.h
/usr/include/net-snmp/agent/null.h
/usr/include/net-snmp/agent/old_api.h
/usr/include/net-snmp/agent/read_only.h
/usr/include/net-snmp/agent/row_merge.h
/usr/include/net-snmp/agent/scalar.h
/usr/include/net-snmp/agent/scalar_group.h
/usr/include/net-snmp/agent/serialize.h
/usr/include/net-snmp/agent/set_helper.h
/usr/include/net-snmp/agent/snmp_agent.h
/usr/include/net-snmp/agent/snmp_get_statistic.h
/usr/include/net-snmp/agent/snmp_vars.h
/usr/include/net-snmp/agent/stash_cache.h
/usr/include/net-snmp/agent/stash_to_next.h
/usr/include/net-snmp/agent/struct.h
/usr/include/net-snmp/agent/sysORTable.h
/usr/include/net-snmp/agent/table.h
/usr/include/net-snmp/agent/table_array.h
/usr/include/net-snmp/agent/table_container.h
/usr/include/net-snmp/agent/table_data.h
/usr/include/net-snmp/agent/table_dataset.h
/usr/include/net-snmp/agent/table_iterator.h
/usr/include/net-snmp/agent/table_tdata.h
/usr/include/net-snmp/agent/util_funcs/
/usr/include/net-snmp/agent/util_funcs.h
/usr/include/net-snmp/agent/util_funcs/MIB_STATS_CACHE_TIMEOUT.h
/usr/include/net-snmp/agent/util_funcs/header_generic.h
/usr/include/net-snmp/agent/util_funcs/header_simple_table.h
/usr/include/net-snmp/agent/var_struct.h
/usr/include/net-snmp/agent/watcher.h