This is a cross-platform sandbox runtime library developed by Anthropic for securely executing untrusted commands within restricted environments. It is designed to be embedded by AI agent runtimes (such as Claude Code) to enforce network and filesystem access controls, perform TLS-terminating HTTP/SOCKS proxying, and mask credentials like API keys and AWS SigV4 secrets. The system operates as a filtering forward proxy with an optional external 'decider' process for per-request allow/deny/body-inspection verdicts, and it supports Linux (via bubblewrap + seccomp), macOS (via Seatbelt profiles), and Windows (via WFP and a Rust helper). The repository is primarily an application library with a CLI tool (`srt`), not a data or research project. It demonstrates high engineering quality with extensive test coverage, careful security invariants, and thoughtful handling of platform edge cases. However, its complexity is extreme—spanning three OS backends, custom proxy servers, TLS MITM, credential injection, and violation monitoring—and it carries significant drift risks from external binary dependencies, runtime-specific workarounds, and a large test surface with conditional skips.