fix: smoke-test agent images after build, add start --no-cache

npm treats optionalDependencies failures as non-fatal, so a transient
network blip fetching claude-code's platform-native binary during
`npm install -g` left a stub CLI in an image that still "built"
successfully — then got baked into the Docker/Container layer cache
until forced to rebuild. Post-build smoke test (provider-declared
argv, run in a throwaway container of the freshly built image) fails
the launch loudly instead of shipping a broken image; --no-cache
gives an escape hatch to force a from-scratch rebuild.

Closes #353.

bot_bottle/backend/macos_container/launch.py

@@ -17,6 +17,7 @@ from contextlib import ExitStack, contextmanager
 from pathlib import Path
 from typing import Callable, Generator
 
+from ...agent_provider import runtime_for
 from ...bottle_state import (
     egress_state_dir,
     git_gate_state_dir,
@@ -169,6 +170,9 @@ def _build_images(plan: MacosContainerBottlePlan) -> MacosContainerBottlePlan:
         _REPO_DIR,
         dockerfile=plan.dockerfile_path,
     )
+    container_mod.verify_agent_image(
+        plan.image, runtime_for(plan.agent_provider_template).smoke_test,
+    )
     return plan