The three concrete-backend package inits eagerly imported their
`*BottleBackend` (which pulls the whole framework), so importing any leaf under
them (e.g. `backend.docker.util`) paid ~78 modules. Give each the same thin
`__getattr__` treatment as the top-level backend package: re-export the public
class(es) lazily on first access, with a TYPE_CHECKING block for checkers.
`import bot_bottle.backend.docker.util` drops from 78 -> 6 bot_bottle modules;
the docker/firecracker/macos-container packages themselves are ~3 each. All
`from bot_bottle.backend.docker import DockerBottleBackend` call-sites and the
lazy selection path keep working.
This is what makes backend leaves cheap — and unblocks moving docker_cmd into
backend/docker/util if we want.
Full unit suite green (2243).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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