Two fixes from the vm4006 rollout (docs/plan/16-git-in-docker-builds.md):
Rootless daemons map the host user to container root, so running the build
container as --user <host-uid> put it into the subuid range and it could not
even create .gradle in a fresh worktree (legacy only worked because its
ownership-repair chown had accidentally moved build/ and .gradle/ into subuid
ownership in its reused primary checkout). The container now always runs as
--user 0: the unprivileged host user under rootless, real root under rootful
where the ownership repair still applies; under rootless it degenerates to 0:0.
Git now works inside build containers: the primary .git is mounted read-only
with .git/gittally/ masked by an empty tmpfs (git.token and the control token
stay unreachable, the workspace bind resurfaces only the build's own worktree)
and the worktree admin dir mounted read-write for index-refreshing commands.
Verified on vm4006: git log/status succeed, the machine config is invisible,
ref writes fail on the read-only mount.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
