AI Engineering/Phase 19/Lesson 26

Capstone Lesson 26: Sandbox Runner with Denylist and Path Jail

The verification gate decides whether a tool call should run. The sandbox decides what happens when it does. This lesson ships a subprocess runner that refuses dangerous executables, refuses dangerous argv shapes, jails every file path to a project root, truncates oversized output, and kills runaway processes on a wall-clock timeout. It is the second of two layers that sit between the model and the operating system.

Build 1.5 hr Python (stdlib)

Prerequisites: Phase 19 · 25 (verification gates and observation budget), Phase 14 · 33 (instructions as constraints), Phase 14 · 38 (verification gates)

#Learning Objectives

Build a Sandbox class wrapping subprocess.run with timeout, capture, and truncation.
Refuse a command by name against a denylist and by structure against an argv inspector.
Refuse any path argument that resolves outside a declared project root.
Refuse shell metacharacters when shell mode is off.
Return a structured SandboxResult that downstream observability and the eval harness can ingest.

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The text and code of this lesson are based on AI Engineering from Scratch by Rohit Ghumare, MIT licensed.