We added support for sharing a single git repository across multiple agents on a host in buildkite-agent v3.10.0.
You can test it out with:
buildkite-agent start \ --experiment git-mirrors \ --git-mirrors-path /tmp/buildkite-git-mirrors
Currently it is just for the main repository, so submodules don’t use a reference repository, nor do plugins.
Keen to hear how folks are using it!