Port the smolmachines backend so BOT_BOTTLE_BACKEND=smolmachines
works on Linux (KVM), not just macOS:
- Preflight gates /dev/kvm presence + accessibility on Linux with
actionable remediation (kvm module, kvm group).
- smolvm state-DB path is platform-derived (XDG on Linux).
- force_allowlist runs on both platforms and is fail-closed: it
verifies the persisted TSI allowlist and dies rather than booting
a VM whose egress confinement it can't confirm. Previously it
no-oped on Linux, failing OPEN.
- allocate() does per-bottle 127.0.0.<N> scoping on Linux too (no
ifconfig needed — all of 127/8 is already loopback); only
ensure_pool's lo0 aliasing stays macOS-only.
- README documents Linux + NixOS host setup.
Linux/KVM integration (the sandbox-escape acceptance gate) is
pending verification on a NixOS host; unit tests cover the new
platform branches.
Issue: #283
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NkwFXLFff9PYPy4wgVBJp9
didericis
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