refactor(backend): generic setup/status; drop firecracker-only CLI

Add abstract `setup()`/`status()` classmethods to BottleBackend (same
per-host, no-instance shape as is_available) so host provisioning is
part of the backend contract, not a per-backend command. Replace the
`./cli.py firecracker {setup,status}` command with a generic
`./cli.py backend {setup,status} [--backend=NAME]` that resolves a
backend (flag / $BOT_BOTTLE_BACKEND / host default) and dispatches —
swapping backends is just a different --backend.

Implementations:
- firecracker: moved out of cli/ into backend/firecracker/setup.py
  (network pool module/script + range-overlap check), unchanged output.
- docker: new backend/docker/setup.py — reports docker on PATH, daemon
  reachability, and gVisor runsc; setup notes no privileged pool is
  needed. Minimal placeholder; richer version tracked in #345.
- macos-container: new setup.py — container CLI + system-service checks.

Also retarget the launch-preflight / isolation-probe pointers to the new
command. New test_cli_backend covers dispatch + docker setup/status.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WBMWTEtQdJ4W5UrWuLHCck

bot_bottle/backend/firecracker/setup.py

@@ -0,0 +1,109 @@
+"""Host setup + status for the Firecracker backend.
+
+`setup()` prints the host-appropriate config for the privileged,
+one-time network pool (TAP devices + isolation nftables table) the
+backend needs. On NixOS it points at the flake module (and prints a
+paste-able fallback); elsewhere it prints the sudo command for the
+bundled setup script. `status()` reports what's present, including
+whether the pool range collides with an existing route.
+
+Called through `FirecrackerBottleBackend.setup` / `.status`, which the
+generic `./cli.py backend {setup,status}` command dispatches to.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+from pathlib import Path
+
+from . import netpool
+
+
+def _owner() -> str:
+    return os.environ.get("USER", "youruser")
+
+
+def _is_nixos() -> bool:
+    if Path("/etc/NIXOS").exists():
+        return True
+    try:
+        return "ID=nixos" in Path("/etc/os-release").read_text()
+    except OSError:
+        return False
+
+
+def _warn_overlaps() -> None:
+    """Warn if the chosen pool range collides with an existing host route
+    (Tailscale CGNAT peer, a docker/libvirt bridge, the LAN…)."""
+    conflicts = netpool.overlapping_routes()
+    if not conflicts:
+        return
+    detail = "\n".join(f"    {c.dst} dev {c.dev}" for c in conflicts)
+    sys.stderr.write(
+        f"WARNING: pool range (base {netpool.ip_base()}, "
+        f"{netpool.pool_size()} slots) overlaps existing routes:\n"
+        f"{detail}\n"
+        "Set BOT_BOTTLE_FC_IP_BASE to a free range before setup, or the "
+        "pool may shadow / be shadowed by the above.\n\n"
+    )
+
+
+def setup() -> int:
+    slots = netpool.all_slots()
+    sys.stderr.write(
+        f"Firecracker network pool: {len(slots)} slots "
+        f"({slots[0].iface}..{slots[-1].iface}), base {netpool.ip_base()}.\n"
+        f"This is a one-time privileged setup (needs root once).\n\n"
+    )
+    _warn_overlaps()
+    if _is_nixos():
+        sys.stderr.write(
+            "Detected NixOS. Preferred: consume the flake module (versioned, "
+            "no copy-paste drift):\n\n"
+            "  # flake inputs (point at wherever you host bot-bottle):\n"
+            "  inputs.bot-bottle.url = \"git+ssh://<your-bot-bottle-remote>\";\n"
+            "  # host module:\n"
+            "  imports = [ inputs.bot-bottle.nixosModules.firecracker-netpool ];\n"
+            f"  services.bot-bottle-firecracker = {{ enable = true; owner = \"{_owner()}\"; }};\n\n"
+            "Then `nixos-rebuild switch`. Channel (non-flake) users can "
+            "`imports = [ <bot-bottle>/nix/firecracker-netpool.nix ];` instead.\n\n"
+            "Fallback — paste this generated module directly:\n\n"
+        )
+        sys.stdout.write(netpool.render_nixos_module())
+    else:
+        sys.stderr.write("Run the one-time setup as root:\n\n")
+        sys.stdout.write(netpool.render_shell_setup() + "\n")
+        sys.stderr.write(
+            "\n(On NixOS, use the declarative module instead — this host "
+            "was not detected as NixOS.)\n"
+        )
+    return 0
+
+
+def status() -> int:
+    ok = True
+    if netpool.nft_table_present():
+        sys.stderr.write(f"nft table inet {netpool.NFT_TABLE}: present\n")
+    else:
+        sys.stderr.write(f"nft table inet {netpool.NFT_TABLE}: MISSING\n")
+        ok = False
+    missing = netpool.missing_taps()
+    total = netpool.pool_size()
+    if missing:
+        sys.stderr.write(f"TAP pool: {total - len(missing)}/{total} present "
+                         f"(missing: {', '.join(missing)})\n")
+        ok = False
+    else:
+        sys.stderr.write(f"TAP pool: {total}/{total} present\n")
+    conflicts = netpool.overlapping_routes()
+    if conflicts:
+        detail = ", ".join(f"{c.dst} dev {c.dev}" for c in conflicts)
+        sys.stderr.write(f"range overlap: base {netpool.ip_base()} CLASHES "
+                         f"with {detail}\n")
+        ok = False
+    else:
+        sys.stderr.write(f"range overlap: none (base {netpool.ip_base()})\n")
+    if not ok:
+        sys.stderr.write("\nRun: ./cli.py backend setup --backend=firecracker\n")
+    return 0 if ok else 1