The version 2.7 currently used for fontsrv:
https://gitlab.freedesktop.org/freetype/freetype/-/archive/VER-2-7/freetype-VER-2-7.tar.gz?ref_type=tags

The latest release (as of 5 Mar 2026) is 2.14.2:
https://gitlab.freedesktop.org/freetype/freetype/-/archive/VER-2-14-2/freetype-VER-2-14-2.tar.bz2?ref_type=tags

The idea is to grab 2.7, bring the changes from fontsrv, then (attempt to) rebase them on 2.14 and work the way.