Adds a Firecracker-based backend for Linux, providing mature KVM-based
microVM isolation to replace smolmachines/libkrun (issue #342, closes
the dead-end tracked in #332).
Architecture:
- Guest control over SSH (dropbear injected into the rootfs) on a
point-to-point TAP link. `ssh -t` forwards SIGWINCH natively, so no
resize bridge is needed.
- Networking: a one-time, root-provisioned pool of user-owned TAP
devices (no shared bridge → no docker0/virbr0/cni0 collisions) plus a
dedicated `table inet bot_bottle_fc` nftables table (independent of
Docker/ufw/firewalld rules). `./cli.py firecracker setup` prints the
host-appropriate config (NixOS module or sudo script).
- Rootfs: `docker export` → ext4 via `mke2fs -d` (rootless, no mount),
cached by image digest; per-bottle SSH pubkey + IP passed via the
kernel cmdline.
- Sidecar: reuses the Docker bundle, published on the slot's host TAP IP.
- Fail-closed isolation: TAP pool verified at preflight; the egress
boundary is proven empirically post-boot (before the agent runs) by a
canary probe — the VM must fail to reach the host directly, or launch
is refused.
Linux hosts with Firecracker + KVM now default to this backend;
macOS stays on macos-container.
Not yet validated end-to-end on live hardware (requires the one-time
network pool). Unit tests + pyright pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01G8p32HJgPoS1hLPWubbftM
Freezer._freeze only ever used bottle.name, which is always
f"bot-bottle-{agent.slug}". Remove the Bottle parameter from
commit() and _freeze(), derive the container name from agent.slug
directly in each subclass, and delete the _NamedBottle stub that
existed solely to paper over this.
Adds a Freezer ABC (backend/freeze.py) that encapsulates the
stop-commit-mark-preserved flow for all backends, following the same
pattern as BottleBackend. Each backend gets its own Freezer subclass:
DockerFreezer — docker commit
MacosContainerFreezer — container export + image rebuild; prompts
to stop if the container is running
SmolmachinesFreezer — smolvm pack create --from-vm
The base class owns write_committed_image, mark_preserved, and the
resume hint. Subclasses implement _freeze() and optionally override
_export_hint() for migration instructions.
Freezer.commit(agent, bottle) is the primary entry point for use
within a live launch context. Freezer.commit_slug(slug) is a
convenience wrapper for cmd_commit, which no longer branches on
backend names itself.
get_freezer(backend_name) is the factory, analogous to
get_bottle_backend(). CommitCancelled is raised by MacosContainerFreezer
when the user declines the stop prompt; cmd_commit catches it and
returns 0.
didericis
didericis-claude