feat(backend): add teardown() to the contract; backend teardown

Add an abstract teardown() classmethod to BottleBackend — the inverse of
setup(), surfaced as `./cli.py backend teardown [--backend=NAME]`
(uninstall). Symmetric with setup: it prints the privileged commands /
declarative config change to remove the host prerequisites.

- firecracker: NixOS-aware — disable the flake module (or drop the
  import) and rebuild, or `firecracker-netpool.sh down` imperatively.
- docker / macos-container: nothing to undo (no privileged host state);
  print a short note.

Not called by the launch path or the test suite. Extends test_cli_backend
for the new dispatch.

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

bot_bottle/backend/__init__.py

@@ -560,6 +560,17 @@ class BottleBackend(ABC, Generic[PlanT, CleanupT]):
         the backend is ready to launch and non-zero when something is
         missing. Invoked by `./cli.py backend status [--backend=…]`."""
 
+    @classmethod
+    @abstractmethod
+    def teardown(cls) -> int:
+        """Undo `setup()` — the inverse operation, surfaced as
+        `./cli.py backend teardown [--backend=…]` (uninstall). Symmetric
+        with setup: where setup is advisory (prints the privileged
+        commands / declarative config to apply), teardown prints the
+        commands / config change to remove the host prerequisites. A
+        backend with no host setup prints a short note and returns 0.
+        Not called by the launch path or the test suite."""
+
 
 # Import concrete backend classes AFTER the base types are defined, so
 # each backend module can pull BottleSpec / BottlePlan / BottleBackend

bot_bottle/backend/docker/backend.py

@@ -64,6 +64,11 @@ class DockerBottleBackend(BottleBackend["DockerBottlePlan", "DockerBottleCleanup
         from . import setup as _setup
         return _setup.status()
 
+    @classmethod
+    def teardown(cls) -> int:
+        from . import setup as _setup
+        return _setup.teardown()
+
     def _preflight(self) -> None:
         _resolve_plan.preflight()
 

bot_bottle/backend/docker/setup.py

@@ -61,6 +61,15 @@ def setup() -> int:
     return 0
 
 
+def teardown() -> int:
+    sys.stderr.write(
+        "Docker backend: nothing to undo — it provisions no privileged host "
+        "state (networks and the sidecar bundle are per-launch and are "
+        "removed by `./cli.py cleanup`). Docker itself is left installed.\n"
+    )
+    return 0
+
+
 def status() -> int:
     ok = True
     if _docker_on_path():

bot_bottle/backend/firecracker/backend.py

@@ -56,6 +56,11 @@ class FirecrackerBottleBackend(
         from . import setup as _setup
         return _setup.status()
 
+    @classmethod
+    def teardown(cls) -> int:
+        from . import setup as _setup
+        return _setup.teardown()
+
     def _preflight(self) -> None:
         _resolve_plan.preflight()
 

bot_bottle/backend/firecracker/setup.py

@@ -81,6 +81,25 @@ def setup() -> int:
     return 0
 
 
+def teardown() -> int:
+    slots = netpool.all_slots()
+    sys.stderr.write(
+        f"Undo the Firecracker network pool ({len(slots)} slots, base "
+        f"{netpool.ip_base()}) — a privileged, one-time operation.\n\n"
+    )
+    if _is_nixos():
+        sys.stderr.write(
+            "On NixOS: set `services.bot-bottle-firecracker.enable = false;` "
+            "(or drop the module import) and `nixos-rebuild switch`. The TAP "
+            "netdevs and nft table are removed declaratively.\n\n"
+            "To tear down imperatively before a rebuild (does not persist):\n\n"
+        )
+    else:
+        sys.stderr.write("Run the teardown as root:\n\n")
+    sys.stdout.write("sudo ./scripts/firecracker-netpool.sh down\n")
+    return 0
+
+
 def status() -> int:
     ok = True
     if netpool.nft_table_present():

bot_bottle/backend/macos_container/backend.py

@@ -46,6 +46,11 @@ class MacosContainerBottleBackend(
         from . import setup as _setup
         return _setup.status()
 
+    @classmethod
+    def teardown(cls) -> int:
+        from . import setup as _setup
+        return _setup.teardown()
+
     def _preflight(self) -> None:
         _resolve_plan.preflight()
 

bot_bottle/backend/macos_container/setup.py

@@ -46,6 +46,16 @@ def setup() -> int:
     return 0
 
 
+def teardown() -> int:
+    sys.stderr.write(
+        "macos-container backend: nothing to undo — it provisions no "
+        "privileged host state. The Apple Container CLI and its system "
+        "service are left as-is (stop the service yourself with "
+        "`container system stop` if you want).\n"
+    )
+    return 0
+
+
 def status() -> int:
     ok = True
     if _container.is_macos():

bot_bottle/cli/__init__.py

@@ -42,7 +42,7 @@ COMMANDS = {
 def usage() -> None:
     sys.stderr.write(f"usage: {PROG} <command> [args...]\n\n")
     sys.stderr.write("Commands:\n")
-    sys.stderr.write("  backend   set up or check a backend's host prerequisites (setup|status)\n")
+    sys.stderr.write("  backend   set up / check / undo a backend's host prerequisites (setup|status|teardown)\n")
     sys.stderr.write("  cleanup   stop and remove all active bot-bottle containers\n")
     sys.stderr.write("  commit    snapshot a running bottle's container state to a Docker image\n")
     sys.stderr.write("  edit      open an agent in vim for editing\n")

bot_bottle/cli/backend.py

@@ -1,12 +1,14 @@
 """`backend` CLI command — generic host setup/status across backends.
 
-`./cli.py backend setup  [--backend=NAME]` provisions (or points at how
+`./cli.py backend setup    [--backend=NAME]` provisions (or points at how
 to provision) the chosen backend's one-time host prerequisites.
-`./cli.py backend status [--backend=NAME]` reports readiness.
+`./cli.py backend status   [--backend=NAME]` reports readiness.
+`./cli.py backend teardown [--backend=NAME]` undoes setup (uninstall).
 
-Both dispatch to the backend's `setup()` / `status()` classmethods, so
+All dispatch to the backend's `setup()` / `status()` / `teardown()`
-there are no backend-specific commands — swapping backends is just a
+classmethods, so there are no backend-specific commands — swapping
-different `--backend` (or `$BOT_BOTTLE_BACKEND`, or the host default).
+backends is just a different `--backend` (or `$BOT_BOTTLE_BACKEND`, or
+the host default).
 """
 
 from __future__ import annotations
@@ -24,8 +26,9 @@ def cmd_backend(args: list[str]) -> int:
     )
     parser.add_argument(
         "action",
-        choices=("setup", "status"),
+        choices=("setup", "status", "teardown"),
-        help="setup: provision/print host prerequisites; status: report readiness",
+        help="setup: provision/print host prerequisites; status: report "
+             "readiness; teardown: undo setup (uninstall)",
     )
     parser.add_argument(
         "--backend",
@@ -38,4 +41,6 @@ def cmd_backend(args: list[str]) -> int:
     backend = get_bottle_backend(ns.backend)
     if ns.action == "setup":
         return backend.setup()
+    if ns.action == "teardown":
+        return backend.teardown()
     return backend.status()

tests/unit/test_cli_backend.py

@@ -21,6 +21,7 @@ class TestCmdBackendDispatch(unittest.TestCase):
         b = MagicMock()
         b.setup.return_value = 0
         b.status.return_value = 3
+        b.teardown.return_value = 0
         return b
 
     def test_setup_dispatches_to_backend(self):
@@ -39,6 +40,14 @@ class TestCmdBackendDispatch(unittest.TestCase):
         b.status.assert_called_once_with()
         self.assertEqual(3, rc)
 
+    def test_teardown_dispatches_to_backend(self):
+        b = self._fake_backend()
+        with patch.object(cmd, "get_bottle_backend", return_value=b):
+            rc = cmd.cmd_backend(["teardown", "--backend", "firecracker"])
+        b.teardown.assert_called_once_with()
+        b.setup.assert_not_called()
+        self.assertEqual(0, rc)
+
     def test_no_backend_flag_uses_host_default(self):
         b = self._fake_backend()
         with patch.object(cmd, "get_bottle_backend", return_value=b) as gbb:
@@ -74,6 +83,9 @@ class TestDockerSetupStatus(unittest.TestCase):
              patch.object(docker_setup._util, "runsc_available", return_value=False):
             self.assertEqual(1, docker_setup.status())
 
+    def test_teardown_is_noop_success(self):
+        self.assertEqual(0, docker_setup.teardown())
+
 
 if __name__ == "__main__":
     unittest.main()