99872e39cd
Addresses review comments 3098, 3099, 3100 on PR #336: - Add BottleImages(agent, sidecar) dataclass to backend/__init__.py. Docker/macOS backends use str image refs; smolmachines uses Path artifacts. Replaces the singular `image` variable from the canonical pattern in comment 3100. - Replace _image_stale_checks/skip_stale with public prelaunch_checks(). CLI now calls backend.prelaunch_checks(plan) before backend.launch(plan); if StaleImageError is raised and the operator confirms, launch proceeds without re-checking. Removes the while-True/skip_stale retry loop. - Add abstract _build_or_load_images(plan) -> BottleImages to BottleBackend. launch() calls it then passes images to _launch_impl. Each backend implements both methods. - Fix comment 3098 (macos-container): _build_images is removed. build_or_load_images() has separate fresh/cached code paths — the cached path never calls a build helper. - Update _start_bundle (smolmachines) to accept sidecar_artifact: Path directly. Sidecar artifact resolution moves to _sidecar_from_path(), called by build_or_load_images alongside _agent_from_path().