Apex publishes the safety rails an autonomous agent needs to run a treasury on Arc. The MIT arc-agent-guardrails library is four fail-closed primitives: send-gate.js enforces per-sender allowlists with per-send and per-day caps and a kill-file; ledger-evm.js records outflows from the on-chain receipt and refuses any value above what the sender declared; vault-exit.js reads Morpho Blue exit liquidity before an ERC-4626 withdrawal; and agent-score.js scores agents against a published ERC-8004 rubric, refusing self-ratings. Each ships with planted-fault and mutation tests. The apex-treasury-operator turns them into an hourly autonomous operator with x402 facilitators and refund flows, and the companion on-chain arc-mandate spending-box enforces the same rules in a contract.