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/smolmachines/launch.py

@@ -22,6 +22,7 @@ from contextlib import ExitStack, contextmanager
 from pathlib import Path
 from typing import Callable, Generator
 
+from ...agent_provider import runtime_for
 from ...egress import (
     EGRESS_ROUTES_IN_CONTAINER,
     egress_agent_env_entries,
@@ -462,10 +463,13 @@ def _agent_from_path(plan: SmolmachinesBottlePlan) -> Path:
     return _ensure_smolmachine(
         plan.agent_image,
         dockerfile=plan.agent_dockerfile_path,
+        smoke_test=runtime_for(plan.agent_provider_template).smoke_test,
     )
 
 
-def _ensure_smolmachine(image_ref: str, *, dockerfile: str = "") -> Path:
+def _ensure_smolmachine(
+    image_ref: str, *, dockerfile: str = "", smoke_test: tuple[str, ...] = (),
+) -> Path:
     """Build the agent docker image and convert it into a
     `.smolmachine` artifact, caching the result under
     `~/.cache/bot-bottle/smolmachines/` keyed by the docker image
@@ -491,6 +495,7 @@ def _ensure_smolmachine(image_ref: str, *, dockerfile: str = "") -> Path:
     already on disk for this image ID."""
     _SMOLMACHINE_CACHE_DIR.mkdir(parents=True, exist_ok=True)
     docker_mod.build_image(image_ref, _REPO_DIR, dockerfile=dockerfile)
+    docker_mod.verify_agent_image(image_ref, smoke_test)
     # `sha256:abcd...` -> `abcd...` first 16 chars: short enough to
     # keep filenames manageable, long enough to make collisions
     # astronomically unlikely.