Podman avoids the CAP_SYS_ADMIN requirement that makes rootless Docker
impossible here: with no subordinate UID range configured it falls back
to a single-UID self-mapping, which an unprivileged process may write
itself, so newuidmap is never invoked. The image build therefore strips
/etc/subuid and /etc/subgid entries rather than adding them.
The agent-facing surface is unchanged — docker and docker compose talk
to podman's Docker-compatible API socket.
Two device nodes need relaxing as root inside the bottle (0666 on
/dev/fuse and /dev/net/tun); both already exist and neither needs a
capability the bottle lacks, unlike CAP_SYS_ADMIN.
Verified live on macOS 26 / Apple Container 1.0.0: service starts with
zero added capabilities, compose pulls and serves from the workspace on
a published port, and a nested container cannot reach the network
outside the egress path.
Known limitation, not yet addressed: the agent base image is Debian
bookworm, whose podman 4.3.1 swallows container exit codes through the
compat API (docker run returns 0 regardless). podman 5.4.2 on trixie
fixes it; the base bump is a separate PR. The acceptance test asserts
on an in-band marker rather than an exit code so it cannot false-pass
in the meantime.
Nested containers give no isolation from the agent itself — root inside
one is the agent user outside it. They are a build/test convenience;
the bottle remains the security boundary.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GnMp8SUGH57hZX7192Rv2F
