argus's review on #5177: the git credential helper answered every `get`,
so a config PR's own flake inputs could have git send the builder's forge
token to any host. The helper is now configured under
`credential.<forge-url>.helper` and itself answers only an https request
whose host is the forge's; a test runs it as git does and checks that
other hosts, http and non-get operations get nothing.
Builds are bounded: every `build_agent` node needs the one `builder` jobq
resource, so one runs at a time and the rest wait pending, and a newer
head cancels its PR's pending build (a running one finishes and writes on
its own commit). The builder also holds a one-permit semaphore around each
build.
`builder` and `review-classifier`, the forge logins swarm-controller owns,
join nix/reserved-names.nix, with a test tying the list to both constants.
The builder is now opt-in like the CI runner: `allSwarmServices` no longer
turns it on, since it runs unreviewed config PRs through the host's nix
daemon. mara had not answered atlas's question on the PR.
cafa120d77