Code interpreter pattern

A code interpreter accepts source text, runs it, and returns output. The important rule is that user code runs in the guest, not in the host process.

One-shot interpreter

mvmctl machine run --runtime python --timeout 10 -- python - <<'PY'
print("hello from inside the sandbox")
PY

Use this shape for stateless calls where every invocation should start clean. Piped stdin reaches the guest only on a transient mvmctl machine run; the top-level mvmctl run does not forward it, so the guest would read EOF.

Persistent interpreter

mvmctl init ./interpreter --preset python
mvmctl machine build --flake ./interpreter
mvmctl machine run --flake ./interpreter --name interpreter -d
mvmctl machine exec interpreter -- python /work/run_cell.py

Use a named VM when you intentionally want cached packages, files, or session state across cells.

Security checklist

• Enforce input size limits before invoking the sandbox.
• Set a timeout.
• Bound stdout/stderr returned to the caller.
• Disable network unless the interpreter needs named endpoints.
• Never pass host credentials through argv.
• Delete or snapshot state intentionally.