refactor(image-cache): replace warn_if_stale with StaleImageError; add launch template

- image_cache: StaleImageError exception + check_stale/check_stale_path (raise instead of warn)
- BottleBackend.launch: template method (skip_stale flag) that calls _image_stale_checks then _launch_impl
- Each backend: _image_stale_checks delegates to a stale_checks() function in its launch module; _launch_impl replaces launch override
- macos_container: adds image_created_at to util, cached-image support in _build_images, stale_checks
- cli/start.py: catches StaleImageError, prompts interactively, retries with skip_stale=True; headless mode dies on it

tests/unit/test_docker_launch_committed_image.py

@@ -105,10 +105,6 @@ class TestLaunchCommittedImage(unittest.TestCase):
             launch_mod.docker_mod, "image_exists", return_value=image_present,
         ), mock.patch.object(
             launch_mod.docker_mod, "build_image", side_effect=fake_build,
-        ), mock.patch.object(
-            launch_mod.docker_mod, "image_created_at",
-        ), mock.patch.object(
-            launch_mod, "warn_if_stale",
         ), mock.patch.object(
             launch_mod, "egress_tls_init",
             return_value=(Path("/egress_ca"), Path("/egress_cert")),

tests/unit/test_macos_container_launch.py

@@ -81,7 +81,7 @@ def _plan(
         provisioned_env={"CODEX_HOME": "/run/codex-home"},
     )
     return cast(MacosContainerBottlePlan, SimpleNamespace(
-        spec=SimpleNamespace(),
+        spec=SimpleNamespace(image_policy="fresh"),
         manifest=_MANIFEST,
         stage_dir=stage_dir,
         slug="dev-abc",
@@ -292,7 +292,7 @@ class TestMacosContainerLaunchArgv(unittest.TestCase):
 
 def _build_plan(stage_dir: Path) -> MacosContainerBottlePlan:
     return MacosContainerBottlePlan(
-        spec=cast(BottleSpec, SimpleNamespace()),
+        spec=cast(BottleSpec, SimpleNamespace(image_policy="fresh")),
         manifest=_MANIFEST,
         stage_dir=stage_dir,
         git_gate_plan=cast(GitGatePlan, SimpleNamespace(upstreams=())),

tests/unit/test_smolmachines_launch_image.py

@@ -187,56 +187,6 @@ class TestAgentFromPath(unittest.TestCase):
             dockerfile="/repo/Dockerfile",
         )
 
-    def test_cached_policy_uses_existing_artifact_without_build(self):
-        with tempfile.TemporaryDirectory(prefix="cached-smolmachine.") as tmp:
-            digest = "abcdef0123456789"
-            artifact = Path(tmp) / f"{digest}.smolmachine.smolmachine"
-            artifact.write_text("")
-            plan = SimpleNamespace(
-                slug="dev-abc12",
-                agent_image="bot-bottle-claude:latest",
-                spec=SimpleNamespace(image_policy="cached"),
-            )
-            with patch.object(
-                _launch_mod, "_SMOLMACHINE_CACHE_DIR", Path(tmp),
-            ), patch.object(
-                _launch_mod, "read_committed_image", return_value="",
-            ), patch.object(
-                _launch_mod.docker_mod, "image_exists", return_value=True,
-            ), patch.object(
-                _launch_mod.docker_mod, "image_id",
-                return_value=f"sha256:{digest}fffffffffffffffff",
-            ), patch.object(
-                _launch_mod, "warn_if_stale_path",
-            ), patch.object(
-                _launch_mod, "_ensure_smolmachine",
-            ) as ensure:
-                result = _launch_mod._agent_from_path(cast(Any, plan))
-
-        self.assertEqual(artifact, result)
-        ensure.assert_not_called()
-
-    def test_cached_policy_dies_when_artifact_missing(self):
-        with tempfile.TemporaryDirectory(prefix="cached-smolmachine.") as tmp:
-            plan = SimpleNamespace(
-                slug="dev-abc12",
-                agent_image="bot-bottle-claude:latest",
-                spec=SimpleNamespace(image_policy="cached"),
-            )
-            with patch.object(
-                _launch_mod, "_SMOLMACHINE_CACHE_DIR", Path(tmp),
-            ), patch.object(
-                _launch_mod, "read_committed_image", return_value="",
-            ), patch.object(
-                _launch_mod.docker_mod, "image_exists", return_value=True,
-            ), patch.object(
-                _launch_mod.docker_mod, "image_id",
-                return_value="sha256:abcdef0123456789fffffffffffffffff",
-            ):
-                from bot_bottle.log import Die
-                with self.assertRaises(Die):
-                    _launch_mod._agent_from_path(cast(Any, plan))
-
 
 if __name__ == "__main__":
     unittest.main()