Ships the smolmachines backend's prepare side: subpackage layout,
`_BACKENDS` registration under "smolmachines", preflight check
for `smolvm` + `gvproxy` on PATH, and the two config-file
renderers (Smolfile TOML + gvproxy YAML). Launch raises
NotImplementedError until chunk 2.

New module layout (mirrors backend/docker/):
  claude_bottle/backend/smolmachines/
    __init__.py            re-exports SmolmachinesBottleBackend
    backend.py             SmolmachinesBottleBackend façade
    bottle.py              SmolmachinesBottle stub (NotImpl until ch2)
    bottle_plan.py         SmolmachinesBottlePlan + .print()
    bottle_cleanup_plan.py SmolmachinesBottleCleanupPlan stub
    prepare.py             resolve_plan: writes both config files
    smolfile.py            TOML renderer (stdlib, no tomli_w dep)
    gvproxy_config.py      YAML renderer (same shape as pipelock_yaml)
    util.py                preflight + per-slug subnet + loopback port

The renderers are pure functions. `resolve_plan` runs the
preflight, allocates one host-side loopback port per active
sidecar (pipelock always; git-gate / supervise conditional),
derives a per-slug gvproxy subnet (hash-mod-254, skipping the
docker-default 17), and writes:

  - <stage>/gvproxy.yaml: subnet + DNS rule resolving only
    `proxy.internal` + port_forwards (one per active sidecar).
  - <stage>/smolfile.toml: guest command/env + virtio-net device
    backed by gvproxy's unixgram socket. No TSI flags — see
    PRD 0023 "Why gvproxy, not TSI".

The agent's HTTPS_PROXY etc. point at `proxy.internal:<gateway-
port>` so the guest dials through gvproxy. gvproxy resolves only
`proxy.internal` → the gateway IP, and forwards exactly the
listed ports to the host-side sidecar bundle (PRD 0024); every
other destination — host LAN, host loopback, public internet
directly — is unreachable by construction.

29 new unit tests covering renderer correctness, subnet
derivation stability + collision-avoidance, loopback port
allocation, and preflight error paths. Full unit suite: 532
passing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

@@ -0,0 +46,4 @@
+        info(f"agent:   {spec.agent_name}")
+        info(f"bottle:  {agent.bottle}")
+        info(f"slug:    {self.slug}")
+        info(f"gvproxy: {self.gvproxy_gateway} on {self.gvproxy_subnet}")

@@ -0,0 +52,4 @@
+        skills = list(agent.skills)
+        upstreams = [g.Name for g in bottle.git]
+        routes = [r.host for r in bottle.egress.routes]
+        info(f"env:     {', '.join(env_names) if env_names else '(none)'}")

@@ -0,0 +55,4 @@
+        info(f"env:     {', '.join(env_names) if env_names else '(none)'}")
+        info(f"skills:  {', '.join(skills) if skills else '(none)'}")
+        info(f"git:     {', '.join(upstreams) if upstreams else '(none)'}")
+        info(f"routes:  {', '.join(routes) if routes else '(none)'}")

@@ -0,0 +56,4 @@
+        info(f"skills:  {', '.join(skills) if skills else '(none)'}")
+        info(f"git:     {', '.join(upstreams) if upstreams else '(none)'}")
+        info(f"routes:  {', '.join(routes) if routes else '(none)'}")
+        info(f"smolfile:       {self.smolfile_path}")

@@ -0,0 +57,4 @@
+        info(f"git:     {', '.join(upstreams) if upstreams else '(none)'}")
+        info(f"routes:  {', '.join(routes) if routes else '(none)'}")
+        info(f"smolfile:       {self.smolfile_path}")
+        info(f"gvproxy config: {self.gvproxy_config_path}")

@@ -0,0 +57,4 @@
+    agent = manifest.agents[spec.agent_name]
+    bottle = manifest.bottle_for(spec.agent_name)
+
+    slug = spec.identity or bottle_identity(spec.agent_name)