Ah this is new in 1.14.0. From https://github.com/flatpak/flatpak/releases/tag/1.14.0 > A "--socket=gpg-agent" option is now recognized by "flatpak run" and related > commands (https://github.com/flatpak/flatpak/pull/4958) This seems to be a manifest option, not a build-time configurable?