/usr/include/ags/ is in libags-gui-dev 1.4.24-1ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/ags/libags-gui.h
/usr/include/ags/widget/
/usr/include/ags/widget/ags_cartesian.h
/usr/include/ags/widget/ags_container.h
/usr/include/ags/widget/ags_dial.h
/usr/include/ags/widget/ags_expander.h
/usr/include/ags/widget/ags_expander_set.h
/usr/include/ags/widget/ags_hindicator.h
/usr/include/ags/widget/ags_hled_array.h
/usr/include/ags/widget/ags_hlevel_box.h
/usr/include/ags/widget/ags_hscale_box.h
/usr/include/ags/widget/ags_htimebar.h
/usr/include/ags/widget/ags_indicator.h
/usr/include/ags/widget/ags_led.h
/usr/include/ags/widget/ags_led_array.h
/usr/include/ags/widget/ags_level.h
/usr/include/ags/widget/ags_level_box.h
/usr/include/ags/widget/ags_notebook.h
/usr/include/ags/widget/ags_piano.h
/usr/include/ags/widget/ags_piano_keys.h
/usr/include/ags/widget/ags_ruler.h
/usr/include/ags/widget/ags_scale.h
/usr/include/ags/widget/ags_scale_box.h
/usr/include/ags/widget/ags_scrolled_level_box.h
/usr/include/ags/widget/ags_scrolled_piano.h
/usr/include/ags/widget/ags_scrolled_scale_box.h
/usr/include/ags/widget/ags_table.h
/usr/include/ags/widget/ags_timebar.h
/usr/include/ags/widget/ags_vindicator.h
/usr/include/ags/widget/ags_vled_array.h
/usr/include/ags/widget/ags_vlevel_box.h
/usr/include/ags/widget/ags_vscale_box.h
/usr/include/ags/widget/ags_waveform.h
/usr/include/ags/widget/ags_widget_marshal.h