Sandbox config boundary

When a feature flag like use_sandbox changes where code runs (host vs container), treat it as a configuration boundary: (1) explicitly provide the container environment your tools expect, and (2) remove/recreate any stateful artifacts created on the other side.

Practical rules:

• Always set container HOME (and cache dirs) explicitly when running as a mapped/non-root UID so tools can write caches:
  • HOME=/tmp
  • UV_CACHE_DIR=/tmp/.cache/uv
  • NPM_CONFIG_CACHE=/tmp/.cache/npm
• If sandboxing is enabled, delete host-created .venv (or any venv-like directory) before running installs/tests inside the container, then recreate it in the sandbox to avoid broken symlinks to host interpreters.

Example (pattern):

def prepare_for_sandbox(project_root: Path, use_sandbox: bool) -> None:
    if use_sandbox:
        stale_venv = project_root / ".venv"
        if stale_venv.is_dir():
            shutil.rmtree(stale_venv)


env = {
    "HOME": "/tmp",
    "UV_CACHE_DIR": "/tmp/.cache/uv",
    "NPM_CONFIG_CACHE": "/tmp/.cache/npm",
}

sandbox_run(
    command=..., 
    workspace=..., 
    network=True,
    env=env,
    # ... other sandbox config ...
)