Address the codex review on #398:
- P1: inject_guest_boot no longer follows a symlink at bb-init/bb-dropbear.
A committed snapshot is guest-controlled and could plant those paths as
symlinks aimed at a host file (e.g. bb-init -> ~/.bashrc); write_text /
copy2 would then overwrite the target as the host user during resume.
Replace any pre-existing entry and create the files with
O_EXCL|O_NOFOLLOW so the write stays inside the staging tree.
- P2: write the snapshot tar owner-only (0600). It can contain the bottle's
private workspace; it was being created world-readable (0644).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UoEZHDjv84ChoZbozQERhJ
The last host-Docker dependency in the Firecracker launch path. Freeze
and resume no longer touch the docker daemon, so the backend needs
firecracker + KVM only — completing #348.
Freeze: stream the guest rootfs over SSH straight into a persistent
committed-rootfs.tar (the resumable/migratable artifact) instead of
round-tripping through `docker build` from a scratch image. Written to
a .partial sibling and atomically renamed so a failed freeze leaves no
truncated artifact.
Resume: extract the snapshot tar into a cached base dir and feed it to
the existing rootless `mke2fs -d` pipeline, replacing the
`docker create` + `docker export | tar` path. Recreate the
proc/sys/dev/run mount points the freezer excludes so the guest init
can mount them.
`util.build_base_rootfs_dir` / `docker_image_id` stay — they still back
the opt-in BOT_BOTTLE_INFRA_BUILD=local dev path and off-host
publish_infra, which are out of scope.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UoEZHDjv84ChoZbozQERhJ
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
didericis