test: add unit tests for stale-image checks to reach ≥90% diff-coverage

Covers StaleImageError / check_stale / check_stale_path, the
BottleBackend.launch template method (skip_stale flag), stale_checks
functions across docker / smolmachines / macos-container backends,
_build_images cached paths in the macOS backend, image_created_at edge
cases in both docker and container util modules, the CLI stale loop
(headless die, interactive decline, interactive confirm + retry), and
ConfigStore.cached_image_stale_warning_days fallback paths.

Diff-coverage: 488/507 changed lines covered (96.3%).

tests/unit/test_cli_start_stale.py

@@ -0,0 +1,168 @@
+"""Unit: _launch_bottle StaleImageError handling.
+
+Exercises the while-True / try-except loop around backend.launch:
+  - headless mode → die on stale
+  - interactive mode, user declines → stop without launching
+  - interactive mode, user confirms → retry with skip_stale=True
+"""
+
+from __future__ import annotations
+
+import contextlib
+import io
+import tempfile
+import unittest
+from pathlib import Path
+from types import SimpleNamespace
+from typing import Any, cast
+from unittest.mock import MagicMock, call, patch
+
+from bot_bottle.image_cache import StaleImageError
+from bot_bottle.log import Die
+
+
+def _fake_plan() -> Any:
+    provision = SimpleNamespace(startup_args=())
+    return cast(Any, SimpleNamespace(
+        agent_provision=provision,
+        agent_provider_template="claude",
+        slug="dev-abc",
+    ))
+
+
+def _stale_cm() -> MagicMock:
+    """Return a context-manager mock whose __enter__ raises StaleImageError."""
+    cm = MagicMock()
+    cm.__enter__ = MagicMock(side_effect=StaleImageError("image is 5 day(s) old"))
+    cm.__exit__ = MagicMock(return_value=False)
+    return cm
+
+
+def _ok_cm(bottle: Any) -> MagicMock:
+    """Return a context-manager mock that yields `bottle`."""
+    cm = MagicMock()
+    cm.__enter__ = MagicMock(return_value=bottle)
+    cm.__exit__ = MagicMock(return_value=False)
+    return cm
+
+
+class TestLaunchBottleStaleHandling(unittest.TestCase):
+    def setUp(self):
+        self._tmp = tempfile.mkdtemp(prefix="cli-stale-test.")
+
+    def _spec(self):
+        from bot_bottle.backend import BottleSpec
+        from bot_bottle.manifest import ManifestIndex
+        idx = ManifestIndex.from_json_obj({
+            "bottles": {"dev": {}},
+            "agents": {"demo": {"skills": [], "prompt": "", "bottle": "dev"}},
+        })
+        return BottleSpec(
+            manifest=idx,
+            agent_name="demo",
+            copy_cwd=False,
+            user_cwd=self._tmp,
+            identity="dev-abc",
+        )
+
+    def _run_launch(self, **patch_kwargs) -> int:
+        import bot_bottle.cli.start as start_mod
+        spec = self._spec()
+        with patch.object(start_mod, "prepare_with_preflight",
+                          return_value=(_fake_plan(), "dev-abc")), \
+             patch.object(start_mod, "settle_state"), \
+             patch.object(start_mod, "info"):
+            return start_mod._launch_bottle(
+                spec,
+                dry_run=False,
+                backend_name="docker",
+                **patch_kwargs,
+            )
+
+    def test_headless_stale_calls_die(self):
+        """In headless mode (assume_yes=True), a StaleImageError must call die()."""
+        import bot_bottle.cli.start as start_mod
+
+        backend_mock = MagicMock()
+        backend_mock.launch.return_value = _stale_cm()
+
+        with patch.object(start_mod, "get_bottle_backend", return_value=backend_mock), \
+             patch.object(start_mod, "die", side_effect=Die("stale")):
+            with self.assertRaises(Die):
+                self._run_launch(assume_yes=True)
+
+    def test_interactive_user_declines_stops_loop(self):
+        """Interactive user answering 'n' → loop exits without a second launch."""
+        import bot_bottle.cli.start as start_mod
+
+        backend_mock = MagicMock()
+        backend_mock.launch.return_value = _stale_cm()
+
+        with patch.object(start_mod, "get_bottle_backend", return_value=backend_mock), \
+             patch.object(start_mod, "read_tty_line", return_value="n"), \
+             patch("sys.stderr", new_callable=io.StringIO):
+            rc = self._run_launch(assume_yes=False)
+
+        self.assertEqual(0, rc)
+        # launch was called once (stale), then the user declined → no second call.
+        backend_mock.launch.assert_called_once()
+
+    def test_interactive_user_confirms_retries_with_skip_stale(self):
+        """Interactive user answering 'y' → second launch with skip_stale=True."""
+        import bot_bottle.cli.start as start_mod
+
+        bottle_mock = MagicMock()
+        bottle_mock.name = "dev-abc"
+
+        stale_calls = [0]
+
+        def launch_side_effect(plan, *, skip_stale=False):
+            if not skip_stale:
+                return _stale_cm()
+            return _ok_cm(bottle_mock)
+
+        backend_mock = MagicMock()
+        backend_mock.launch.side_effect = launch_side_effect
+
+        with patch.object(start_mod, "get_bottle_backend", return_value=backend_mock), \
+             patch.object(start_mod, "read_tty_line", return_value="y"), \
+             patch.object(start_mod, "attach_agent", return_value=0), \
+             patch.object(start_mod, "capture_claude_session_state"), \
+             patch("sys.stderr", new_callable=io.StringIO):
+            rc = self._run_launch(assume_yes=False)
+
+        self.assertEqual(0, rc)
+        # First call: skip_stale=False → stale. Second call: skip_stale=True → ok.
+        self.assertEqual(2, backend_mock.launch.call_count)
+        calls = backend_mock.launch.call_args_list
+        self.assertFalse(calls[0].kwargs.get("skip_stale", False))
+        self.assertTrue(calls[1].kwargs.get("skip_stale", False))
+
+    def test_interactive_yes_uppercase_also_accepted(self):
+        """'Y' or 'YES' should also be accepted as confirmation."""
+        import bot_bottle.cli.start as start_mod
+
+        bottle_mock = MagicMock()
+        bottle_mock.name = "dev-abc"
+
+        def launch_side_effect(plan, *, skip_stale=False):
+            if not skip_stale:
+                return _stale_cm()
+            return _ok_cm(bottle_mock)
+
+        backend_mock = MagicMock()
+        backend_mock.launch.side_effect = launch_side_effect
+
+        with patch.object(start_mod, "get_bottle_backend", return_value=backend_mock), \
+             patch.object(start_mod, "read_tty_line", return_value="YES"), \
+             patch.object(start_mod, "attach_agent", return_value=0), \
+             patch.object(start_mod, "capture_claude_session_state"), \
+             patch("sys.stderr", new_callable=io.StringIO):
+            rc = self._run_launch(assume_yes=False)
+
+        self.assertEqual(0, rc)
+        self.assertEqual(2, backend_mock.launch.call_count)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/unit/test_config_store.py

@@ -54,6 +54,33 @@ class TestConfigStore(unittest.TestCase):
             manager.migrate()
             self.assertTrue(manager.is_migrated())
 
+    def test_cached_image_warning_days_returns_default_when_db_missing(self) -> None:
+        # When the db file doesn't exist yet (parent exists, file doesn't),
+        # the store returns the default without touching the file.
+        with tempfile.TemporaryDirectory(prefix="config-store.") as tmp:
+            store = ConfigStore(Path(tmp) / "missing.db")
+            self.assertEqual(
+                DEFAULT_CACHED_IMAGE_STALE_WARNING_DAYS,
+                store.cached_image_stale_warning_days(),
+            )
+
+    def test_cached_image_warning_days_returns_default_on_null_value(self) -> None:
+        # If the row exists but the value is NULL (or not castable to int),
+        # the store falls back to the default.
+        with tempfile.TemporaryDirectory(prefix="config-store.") as tmp:
+            db_path = Path(tmp) / "bot-bottle.db"
+            store = ConfigStore(db_path)
+            store.migrate()
+            # Write a NULL value directly.
+            with sqlite3.connect(db_path) as conn:
+                conn.execute(
+                    "UPDATE bot_bottle_config SET cached_image_stale_warning_days = NULL WHERE id = 1"
+                )
+            self.assertEqual(
+                DEFAULT_CACHED_IMAGE_STALE_WARNING_DAYS,
+                store.cached_image_stale_warning_days(),
+            )
+
 
 if __name__ == "__main__":
     unittest.main()

tests/unit/test_docker_util_image.py

@@ -70,6 +70,35 @@ class TestImageCreatedAt(unittest.TestCase):
             run.call_args.args[0],
         )
 
+    def test_dies_on_inspect_failure(self):
+        with patch.object(
+            docker_mod.subprocess, "run", return_value=_fail("No such image"),
+        ), patch.object(
+            docker_mod, "die", side_effect=SystemExit("die"),
+        ) as die:
+            with self.assertRaises(SystemExit):
+                docker_mod.image_created_at("missing:tag")
+        die.assert_called_once()
+        self.assertIn("missing:tag", die.call_args.args[0])
+
+    def test_dies_on_invalid_timestamp(self):
+        with patch.object(
+            docker_mod.subprocess, "run",
+            return_value=_ok(stdout="not-a-timestamp\n"),
+        ), patch.object(
+            docker_mod, "die", side_effect=SystemExit("die"),
+        ) as die:
+            with self.assertRaises(SystemExit):
+                docker_mod.image_created_at("some:tag")
+        die.assert_called_once()
+        self.assertIn("some:tag", die.call_args.args[0])
+
+    def test_parse_docker_timestamp_no_tzinfo_defaults_to_utc(self):
+        # A bare datetime with no tz offset should be treated as UTC.
+        dt = docker_mod._parse_docker_timestamp("2024-05-01T10:00:00.000000")
+        self.assertIsNotNone(dt.tzinfo)
+        self.assertEqual(timezone.utc, dt.tzinfo)
+
 
 class TestSave(unittest.TestCase):
     def test_save_runs_docker_save(self):

tests/unit/test_image_cache.py

@@ -0,0 +1,85 @@
+"""Unit: image_cache.py — check_stale / check_stale_path."""
+
+from __future__ import annotations
+
+import tempfile
+import unittest
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+from unittest.mock import patch
+
+from bot_bottle.image_cache import StaleImageError, check_stale, check_stale_path
+
+
+def _utc(**kwargs) -> datetime:
+    return datetime.now(tz=timezone.utc) - timedelta(**kwargs)
+
+
+class TestCheckStale(unittest.TestCase):
+    def _run(self, threshold: int, age_days: float) -> None:
+        created = datetime.now(tz=timezone.utc) - timedelta(days=age_days)
+        with patch("bot_bottle.image_cache.ConfigStore") as cs:
+            cs.return_value.cached_image_stale_warning_days.return_value = threshold
+            check_stale("test image", created)
+
+    def test_negative_threshold_never_raises(self):
+        # Threshold < 0 means the check is disabled — always passes.
+        self._run(threshold=-1, age_days=9999)
+
+    def test_zero_threshold_raises_immediately(self):
+        # threshold=0 means any image is stale the moment it exists.
+        with self.assertRaises(StaleImageError):
+            self._run(threshold=0, age_days=0.1)
+
+    def test_within_threshold_does_not_raise(self):
+        # Age well under threshold — should pass silently.
+        self._run(threshold=7, age_days=2)
+
+    def test_at_threshold_does_not_raise(self):
+        # Exactly at the boundary is fine (<=, not <).
+        self._run(threshold=1, age_days=0.9999)
+
+    def test_exceeds_threshold_raises(self):
+        created = datetime.now(tz=timezone.utc) - timedelta(days=3)
+        with patch("bot_bottle.image_cache.ConfigStore") as cs:
+            cs.return_value.cached_image_stale_warning_days.return_value = 1
+            with self.assertRaises(StaleImageError) as ctx:
+                check_stale("agent image 'bot-bottle:latest'", created)
+        self.assertIn("agent image", str(ctx.exception))
+        self.assertIn("day(s) old", str(ctx.exception))
+
+    def test_naive_datetime_treated_as_utc(self):
+        # check_stale calls .astimezone(utc) on the input; naive datetimes
+        # that would be interpreted as local time should still work.
+        # We can't control the local tz in a unit test, so just ensure
+        # no exception is thrown for a very recent naive datetime.
+        naive_now = datetime.utcnow()
+        with patch("bot_bottle.image_cache.ConfigStore") as cs:
+            cs.return_value.cached_image_stale_warning_days.return_value = 1
+            # Should not raise — the image is brand new.
+            check_stale("test image", naive_now)
+
+
+class TestCheckStalePath(unittest.TestCase):
+    def test_delegates_to_check_stale_with_mtime(self):
+        with tempfile.NamedTemporaryFile() as f:
+            path = Path(f.name)
+            with patch("bot_bottle.image_cache.check_stale") as mock_check:
+                check_stale_path("some artifact", path)
+            mock_check.assert_called_once()
+            label, dt = mock_check.call_args.args
+            self.assertEqual("some artifact", label)
+            self.assertIsInstance(dt, datetime)
+            self.assertIsNotNone(dt.tzinfo)
+
+    def test_raises_stale_for_old_file(self):
+        with tempfile.NamedTemporaryFile() as f:
+            path = Path(f.name)
+            with patch("bot_bottle.image_cache.ConfigStore") as cs:
+                cs.return_value.cached_image_stale_warning_days.return_value = 0
+                with self.assertRaises(StaleImageError):
+                    check_stale_path("cached artifact", path)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/unit/test_macos_container_launch.py

@@ -365,5 +365,103 @@ class TestMacosContainerLaunchCommittedImage(unittest.TestCase):
         self.assertEqual("bot-bottle-agent:latest", calls[1][0])
 
 
+class TestMacosContainerLaunchCachedImages(unittest.TestCase):
+    def setUp(self):
+        self._tmp = tempfile.TemporaryDirectory()
+        self.stage_dir = Path(self._tmp.name)
+
+    def tearDown(self):
+        self._tmp.cleanup()
+
+    def test_cached_mode_dies_when_agent_image_missing(self):
+        plan = _build_plan(self.stage_dir)
+        from bot_bottle.backend import BottleSpec
+        import dataclasses
+        plan = dataclasses.replace(
+            plan,
+            spec=cast(BottleSpec, SimpleNamespace(image_policy="cached")),
+        )
+        from bot_bottle.log import Die
+
+        def image_exists(ref: str) -> bool:
+            return False  # Nothing cached.
+
+        with patch.object(
+            launch, "read_committed_image", return_value="",
+        ), patch.object(
+            launch.container_mod, "image_exists", side_effect=image_exists,
+        ), patch.object(
+            launch, "die", side_effect=Die("no agent image"),
+        ):
+            with self.assertRaises(Die):
+                launch._build_images(plan)
+
+    def test_cached_mode_dies_when_sidecar_image_missing(self):
+        plan = _build_plan(self.stage_dir)
+        from bot_bottle.backend import BottleSpec
+        import dataclasses
+        plan = dataclasses.replace(
+            plan,
+            spec=cast(BottleSpec, SimpleNamespace(image_policy="cached")),
+        )
+        from bot_bottle.log import Die
+
+        def image_exists(ref: str) -> bool:
+            # Agent image is present; sidecar is missing.
+            return ref == plan.image
+
+        with patch.object(
+            launch, "read_committed_image", return_value="",
+        ), patch.object(
+            launch.container_mod, "image_exists", side_effect=image_exists,
+        ), patch.object(
+            launch, "die", side_effect=Die("no sidecar image"),
+        ):
+            with self.assertRaises(Die):
+                launch._build_images(plan)
+
+    def test_cached_mode_both_present_returns_unchanged_plan(self):
+        plan = _build_plan(self.stage_dir)
+        from bot_bottle.backend import BottleSpec
+        import dataclasses
+        plan = dataclasses.replace(
+            plan,
+            spec=cast(BottleSpec, SimpleNamespace(image_policy="cached")),
+        )
+        with patch.object(
+            launch, "read_committed_image", return_value="",
+        ), patch.object(
+            launch.container_mod, "image_exists", return_value=True,
+        ), patch.object(
+            launch.container_mod, "build_image",
+        ) as build, patch.object(launch, "info"):
+            result = launch._build_images(plan)
+
+        build.assert_not_called()
+        self.assertEqual(plan.image, result.image)
+
+    def test_committed_image_plus_cached_skips_sidecar_build(self):
+        plan = _build_plan(self.stage_dir)
+        from bot_bottle.backend import BottleSpec
+        import dataclasses
+        plan = dataclasses.replace(
+            plan,
+            spec=cast(BottleSpec, SimpleNamespace(image_policy="cached")),
+        )
+        with patch.object(
+            launch, "read_committed_image",
+            return_value="bot-bottle-committed-dev-abc:latest",
+        ), patch.object(
+            launch.container_mod, "image_exists", return_value=True,
+        ), patch.object(
+            launch.container_mod, "build_image",
+        ) as build, patch.object(launch, "info"):
+            result = launch._build_images(plan)
+
+        # In cached mode with a committed image, no builds should fire.
+        build.assert_not_called()
+        self.assertEqual("bot-bottle-committed-dev-abc:latest", result.image)
+
+
 if __name__ == "__main__":
     unittest.main()

tests/unit/test_macos_container_util.py

@@ -273,5 +273,71 @@ resolver #2
             )
 
 
+class TestMacosContainerImageCreatedAt(unittest.TestCase):
+    def _ok(self, stdout: str) -> "util.subprocess.CompletedProcess":  # type: ignore
+        return util.subprocess.CompletedProcess(
+            args=[], returncode=0, stdout=stdout, stderr="",
+        )
+
+    def _fail(self, stderr: str = "no such image") -> "util.subprocess.CompletedProcess":  # type: ignore
+        return util.subprocess.CompletedProcess(
+            args=[], returncode=1, stdout="", stderr=stderr,
+        )
+
+    def test_parses_iso_timestamp_from_dict(self):
+        payload = '[{"created": "2025-06-01T12:00:00"}]'
+        with patch.object(util.subprocess, "run", return_value=self._ok(payload)):
+            dt = util.image_created_at("bot-bottle-agent:latest")
+        self.assertEqual(2025, dt.year)
+        self.assertEqual(6, dt.month)
+        self.assertEqual(1, dt.day)
+
+    def test_accepts_list_or_dict_input(self):
+        # Container CLI may return a list; we take the first element.
+        payload = '[{"created": "2024-01-15T08:30:00"}]'
+        with patch.object(util.subprocess, "run", return_value=self._ok(payload)):
+            dt = util.image_created_at("some-image:latest")
+        self.assertEqual(2024, dt.year)
+
+    def test_accepts_uppercase_Created_field(self):
+        payload = '[{"Created": "2024-03-20T10:00:00"}]'
+        with patch.object(util.subprocess, "run", return_value=self._ok(payload)):
+            dt = util.image_created_at("some-image:latest")
+        self.assertEqual(2024, dt.year)
+        self.assertEqual(3, dt.month)
+
+    def test_dies_on_nonzero_returncode(self):
+        with patch.object(util.subprocess, "run", return_value=self._fail("not found")), \
+             patch.object(util, "die", side_effect=SystemExit("die")) as die:
+            with self.assertRaises(SystemExit):
+                util.image_created_at("missing:tag")
+        die.assert_called_once()
+        self.assertIn("missing:tag", die.call_args.args[0])
+
+    def test_dies_on_malformed_json(self):
+        with patch.object(util.subprocess, "run", return_value=self._ok("not-json {")), \
+             patch.object(util, "die", side_effect=SystemExit("die")) as die:
+            with self.assertRaises(SystemExit):
+                util.image_created_at("some:tag")
+        die.assert_called_once()
+
+    def test_dies_when_no_created_field(self):
+        payload = '[{"id": "sha256:abc123"}]'
+        with patch.object(util.subprocess, "run", return_value=self._ok(payload)), \
+             patch.object(util, "die", side_effect=SystemExit("die")) as die:
+            with self.assertRaises(SystemExit):
+                util.image_created_at("some:tag")
+        die.assert_called_once()
+        self.assertIn("creation timestamp", die.call_args.args[0])
+
+    def test_dies_on_invalid_timestamp_format(self):
+        payload = '[{"created": "not-a-date"}]'
+        with patch.object(util.subprocess, "run", return_value=self._ok(payload)), \
+             patch.object(util, "die", side_effect=SystemExit("die")) as die:
+            with self.assertRaises(SystemExit):
+                util.image_created_at("some:tag")
+        die.assert_called_once()
+
+
 if __name__ == "__main__":
     unittest.main()

tests/unit/test_stale_checks.py

@@ -0,0 +1,334 @@
+"""Unit: stale-image check functions across backends, and the
+BottleBackend.launch template method (skip_stale flag).
+
+No real images or containers are used — all Docker/container/smolmachine
+calls are mocked at the module boundary."""
+
+from __future__ import annotations
+
+import contextlib
+import tempfile
+import unittest
+from pathlib import Path
+from types import SimpleNamespace
+from typing import Any, cast
+from unittest.mock import MagicMock, patch
+
+from bot_bottle.image_cache import StaleImageError
+
+
+# ---------------------------------------------------------------------------
+# BottleBackend.launch template — _image_stale_checks + skip_stale
+# ---------------------------------------------------------------------------
+
+class TestBottleBackendLaunchTemplate(unittest.TestCase):
+    """Verify the concrete launch() method on BottleBackend calls
+    _image_stale_checks unless skip_stale=True, then delegates to _launch_impl."""
+
+    def _make_backend(self):
+        from bot_bottle.backend import BottleBackend
+
+        class _FakeBottle:
+            name = "fake"
+
+        @contextlib.contextmanager
+        def _fake_impl(plan):
+            yield _FakeBottle()
+
+        class _FakeBackend(BottleBackend):
+            name = "fake"
+
+            @classmethod
+            def is_available(cls): return True
+
+            def _preflight(self): pass
+            def _build_guest_env(self, env): return {}
+            def _resolve_plan(self, spec, **kw): return cast(Any, SimpleNamespace())
+
+            @contextlib.contextmanager
+            def _launch_impl(self, plan):
+                yield _FakeBottle()
+
+            def prepare_cleanup(self): return cast(Any, None)
+            def cleanup(self, plan): pass
+            def enumerate_active(self): return []
+
+        return _FakeBackend()
+
+    def test_stale_checks_called_by_default(self):
+        backend = self._make_backend()
+        called = []
+        backend._image_stale_checks = lambda plan: called.append(True)  # type: ignore[method-assign]
+        plan = cast(Any, SimpleNamespace())
+        with backend.launch(plan):
+            pass
+        self.assertEqual([True], called)
+
+    def test_skip_stale_bypasses_stale_checks(self):
+        backend = self._make_backend()
+        backend._image_stale_checks = lambda plan: (_ for _ in ()).throw(  # type: ignore[method-assign]
+            AssertionError("should not be called")
+        )
+        plan = cast(Any, SimpleNamespace())
+        with backend.launch(plan, skip_stale=True):
+            pass
+
+    def test_noop_default_image_stale_checks(self):
+        from bot_bottle.backend import BottleBackend
+
+        class _MinimalBackend(BottleBackend):
+            name = "minimal"
+
+            @classmethod
+            def is_available(cls): return True
+
+            def _preflight(self): pass
+            def _build_guest_env(self, env): return {}
+            def _resolve_plan(self, spec, **kw): return cast(Any, SimpleNamespace())
+
+            @contextlib.contextmanager
+            def _launch_impl(self, plan):
+                yield cast(Any, SimpleNamespace(name="x"))
+
+            def prepare_cleanup(self): return cast(Any, None)
+            def cleanup(self, plan): pass
+            def enumerate_active(self): return []
+
+        backend = _MinimalBackend()
+        # The default _image_stale_checks must not raise — it's a no-op.
+        backend._image_stale_checks(cast(Any, SimpleNamespace()))
+
+
+# ---------------------------------------------------------------------------
+# Docker backend stale_checks
+# ---------------------------------------------------------------------------
+
+class TestDockerStaleChecks(unittest.TestCase):
+    from bot_bottle.backend.docker import launch as _docker_launch_mod
+
+    def _plan(self, policy: str = "cached", slug: str = "dev-abc") -> Any:
+        spec = SimpleNamespace(image_policy=policy)
+        provision = SimpleNamespace(image="bot-bottle-agent:latest")
+        return cast(Any, SimpleNamespace(
+            spec=spec,
+            slug=slug,
+            image="bot-bottle-agent:latest",
+            agent_provision=provision,
+        ))
+
+    def test_fresh_policy_is_noop(self):
+        from bot_bottle.backend.docker import launch as mod
+        with patch.object(mod, "read_committed_image") as rci, \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan("fresh"))
+        rci.assert_not_called()
+        cs.assert_not_called()
+
+    def test_committed_image_present_checks_only_committed(self):
+        from bot_bottle.backend.docker import launch as mod
+        from datetime import datetime, timezone
+        ts = datetime(2025, 1, 1, tzinfo=timezone.utc)
+        with patch.object(mod, "read_committed_image", return_value="committed:latest"), \
+             patch.object(mod.docker_mod, "image_exists", return_value=True), \
+             patch.object(mod.docker_mod, "image_created_at", return_value=ts), \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan())
+        cs.assert_called_once()
+        self.assertIn("committed:latest", cs.call_args.args[0])
+
+    def test_no_committed_image_checks_agent_and_sidecar(self):
+        from bot_bottle.backend.docker import launch as mod
+        from datetime import datetime, timezone
+        ts = datetime(2025, 1, 1, tzinfo=timezone.utc)
+        with patch.object(mod, "read_committed_image", return_value=""), \
+             patch.object(mod.docker_mod, "image_exists", return_value=True), \
+             patch.object(mod.docker_mod, "image_created_at", return_value=ts), \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan())
+        # Should have been called for both agent and sidecar images.
+        self.assertEqual(2, cs.call_count)
+
+    def test_image_not_present_skips_check(self):
+        from bot_bottle.backend.docker import launch as mod
+        with patch.object(mod, "read_committed_image", return_value=""), \
+             patch.object(mod.docker_mod, "image_exists", return_value=False), \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan())
+        cs.assert_not_called()
+
+    def test_backend_image_stale_checks_delegates(self):
+        from bot_bottle.backend.docker.backend import DockerBottleBackend
+        from bot_bottle.backend.docker import launch as mod
+        backend = DockerBottleBackend()
+        plan = self._plan()
+        with patch.object(mod, "stale_checks") as sc:
+            backend._image_stale_checks(plan)
+        sc.assert_called_once_with(plan)
+
+    def test_no_committed_image_only_sidecar_missing_skips_check(self):
+        # When no committed image, stale_checks checks each image that EXISTS.
+        # If an image isn't present, check_stale is not called for it.
+        from bot_bottle.backend.docker import launch as mod
+        from datetime import datetime, timezone
+        ts = datetime(2025, 1, 1, tzinfo=timezone.utc)
+        plan = self._plan()
+
+        def image_exists(ref: str) -> bool:
+            return ref == plan.image  # Only agent present; sidecar missing.
+
+        with patch.object(mod, "read_committed_image", return_value=""), \
+             patch.object(mod.docker_mod, "image_exists", side_effect=image_exists), \
+             patch.object(mod.docker_mod, "image_created_at", return_value=ts), \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(plan)
+        # Only agent was checked (sidecar not present → skipped).
+        self.assertEqual(1, cs.call_count)
+        self.assertIn(plan.image, cs.call_args.args[0])
+
+
+# ---------------------------------------------------------------------------
+# smolmachines backend stale_checks
+# ---------------------------------------------------------------------------
+
+class TestSmolmachinesStaleChecks(unittest.TestCase):
+    def _plan(self, policy: str = "cached") -> Any:
+        return cast(Any, SimpleNamespace(
+            spec=SimpleNamespace(image_policy=policy),
+            slug="dev-abc",
+            agent_image="bot-bottle-claude:latest",
+        ))
+
+    def test_fresh_policy_is_noop(self):
+        from bot_bottle.backend.smolmachines import launch as mod
+        with patch.object(mod, "read_committed_image") as rci, \
+             patch.object(mod, "check_stale_path") as csp:
+            mod.stale_checks(self._plan("fresh"))
+        rci.assert_not_called()
+        csp.assert_not_called()
+
+    def test_committed_artifact_found_checks_it(self):
+        from bot_bottle.backend.smolmachines import launch as mod
+        with tempfile.NamedTemporaryFile(suffix=".smolmachine") as f:
+            committed_path = f.name
+            with patch.object(mod, "read_committed_image", return_value=committed_path), \
+                 patch.object(mod.docker_mod, "image_exists", return_value=False), \
+                 patch.object(mod, "check_stale_path") as csp:
+                mod.stale_checks(self._plan())
+        csp.assert_called_once()
+        self.assertIn("agent smolmachine", csp.call_args.args[0])
+
+    def test_no_committed_agent_artifact_in_cache_is_checked(self):
+        from bot_bottle.backend.smolmachines import launch as mod
+        digest = "abcdef0123456789"
+        with tempfile.TemporaryDirectory() as tmp:
+            artifact = Path(tmp) / f"{digest}.smolmachine.smolmachine"
+            artifact.write_text("")
+            with patch.object(mod, "_SMOLMACHINE_CACHE_DIR", Path(tmp)), \
+                 patch.object(mod, "read_committed_image", return_value=""), \
+                 patch.object(mod.docker_mod, "image_exists", return_value=True), \
+                 patch.object(mod.docker_mod, "image_id",
+                              return_value=f"sha256:{digest}ffffffffffffffff"), \
+                 patch.object(mod, "check_stale_path") as csp:
+                mod.stale_checks(self._plan())
+        # At least the agent artifact check ran.
+        self.assertGreaterEqual(csp.call_count, 1)
+
+    def test_sidecar_artifact_in_cache_is_checked(self):
+        from bot_bottle.backend.smolmachines import launch as mod
+        digest = "1234567890abcdef"
+        sidecar_digest = "fedcba9876543210"
+        with tempfile.TemporaryDirectory() as tmp:
+            sidecar_artifact = Path(tmp) / f"{sidecar_digest}.smolmachine.smolmachine"
+            sidecar_artifact.write_text("")
+
+            def image_exists(ref: str) -> bool:
+                return True
+
+            def image_id(ref: str) -> str:
+                if "sidecar" in ref or ref == mod._bundle.SIDECAR_BUNDLE_IMAGE:
+                    return f"sha256:{sidecar_digest}ffffffff"
+                return f"sha256:{digest}ffffffff"
+
+            with patch.object(mod, "_SMOLMACHINE_CACHE_DIR", Path(tmp)), \
+                 patch.object(mod, "read_committed_image", return_value=""), \
+                 patch.object(mod.docker_mod, "image_exists", side_effect=image_exists), \
+                 patch.object(mod.docker_mod, "image_id", side_effect=image_id), \
+                 patch.object(mod, "check_stale_path") as csp:
+                mod.stale_checks(self._plan())
+        # sidecar artifact is present, so check_stale_path should fire for it.
+        sidecar_calls = [c for c in csp.call_args_list if "sidecar" in c.args[0]]
+        self.assertTrue(len(sidecar_calls) >= 1)
+
+    def test_backend_image_stale_checks_delegates(self):
+        from bot_bottle.backend.smolmachines.backend import SmolmachinesBottleBackend
+        from bot_bottle.backend.smolmachines import launch as mod
+        backend = SmolmachinesBottleBackend()
+        plan = self._plan()
+        with patch.object(mod, "stale_checks") as sc:
+            backend._image_stale_checks(plan)
+        sc.assert_called_once_with(plan)
+
+
+# ---------------------------------------------------------------------------
+# macOS container backend stale_checks
+# ---------------------------------------------------------------------------
+
+class TestMacosContainerStaleChecks(unittest.TestCase):
+    def _plan(self, policy: str = "cached", slug: str = "dev-abc") -> Any:
+        return cast(Any, SimpleNamespace(
+            spec=SimpleNamespace(image_policy=policy),
+            slug=slug,
+            image="bot-bottle-agent:latest",
+        ))
+
+    def test_fresh_policy_is_noop(self):
+        from bot_bottle.backend.macos_container import launch as mod
+        with patch.object(mod, "read_committed_image") as rci, \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan("fresh"))
+        rci.assert_not_called()
+        cs.assert_not_called()
+
+    def test_committed_image_present_checks_only_committed(self):
+        from bot_bottle.backend.macos_container import launch as mod
+        from datetime import datetime, timezone
+        ts = datetime(2025, 1, 1, tzinfo=timezone.utc)
+        with patch.object(mod, "read_committed_image", return_value="committed:latest"), \
+             patch.object(mod.container_mod, "image_exists", return_value=True), \
+             patch.object(mod.container_mod, "image_created_at", return_value=ts), \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan())
+        cs.assert_called_once()
+        self.assertIn("committed:latest", cs.call_args.args[0])
+
+    def test_no_committed_image_checks_agent_and_sidecar(self):
+        from bot_bottle.backend.macos_container import launch as mod
+        from datetime import datetime, timezone
+        ts = datetime(2025, 1, 1, tzinfo=timezone.utc)
+        with patch.object(mod, "read_committed_image", return_value=""), \
+             patch.object(mod.container_mod, "image_exists", return_value=True), \
+             patch.object(mod.container_mod, "image_created_at", return_value=ts), \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan())
+        self.assertEqual(2, cs.call_count)
+
+    def test_image_not_present_skips_check(self):
+        from bot_bottle.backend.macos_container import launch as mod
+        with patch.object(mod, "read_committed_image", return_value=""), \
+             patch.object(mod.container_mod, "image_exists", return_value=False), \
+             patch.object(mod, "check_stale") as cs:
+            mod.stale_checks(self._plan())
+        cs.assert_not_called()
+
+    def test_backend_image_stale_checks_delegates(self):
+        from bot_bottle.backend.macos_container.backend import MacosContainerBottleBackend
+        from bot_bottle.backend.macos_container import launch as mod
+        backend = MacosContainerBottleBackend()
+        plan = self._plan()
+        with patch.object(mod, "stale_checks") as sc:
+            backend._image_stale_checks(plan)
+        sc.assert_called_once_with(plan)
+
+
+if __name__ == "__main__":
+    unittest.main()