Pactra: Hierarchical On-Chain Budget Enforcement for Delegated Autonomous Agent Systems

Pactra is a hierarchical, on-chain budget-enforcement mechanism designed for autonomous-agent systems in which agents can delegate tasks and spending authority to other agents. Conventional per-agent spending limits become insufficient in hierarchical environments because independently funded descendants may collectively spend more than the root owner intended to authorize. Pactra addresses this problem by enforcing spending constraints across the complete delegation path.

The protocol represents agents as nodes in a mandate tree. Every ordinary expenditure requested by a node is evaluated against and debited from the corresponding spending counters of that node and each of its ancestors. Child mandates must satisfy a narrowing rule: their budgets, transaction limits, lifetimes, concentration limits, and delegation depth cannot exceed the authority granted by their parent. This construction preserves root-level and subtree-level budget bounds as authority is delegated across multiple agent generations.

Pactra is implemented through Solidity smart contracts and supporting TypeScript services. Its architecture separates mandate management, treasury accounting, payment execution, conduct attestation, indexing, and agent-facing tools. Agent tools do not receive the operator’s private key, while the on-chain contracts independently evaluate applicable mandate constraints before accepting an ordinary draw.

The evaluation combines unit and integration testing, fuzz testing, stateful invariant campaigns, scripted adversarial spending searches, reproducible gas measurements, and comparative experiments. The evaluated implementation passes 101 Foundry-reported test cases across 16 suites. A scenario-driven adversarial search evaluates 1,200 generated spending strategies comprising 45,360 individual draw attempts. A controlled depth sweep additionally measures how transaction cost changes as the length of the delegation path increases. Pactra is compared with shared-cap and independent-wallet baselines under equivalent local experimental conditions.

The paper distinguishes carefully between properties enforced by smart contracts and guarantees that depend on trusted off-chain components. In particular, owner-authorized overrides are excluded from the ordinary-draw conservation invariant; draw and settlement operations are non-atomic; and the counterparty address supplied by the payment daemon is not cryptographically bound to the recipient of the subsequent payment authorization. Other documented limitations include depth-dependent gas costs, residual DNS time-of-check-to-time-of-use risk, reliance on trusted external contracts, and the absence of formal or symbolic verification.

This Zenodo record contains the research preprint and its reproducible LaTeX source package. The associated implementation, contract tests, evaluation harnesses, benchmark scripts, and research artifacts are available through the linked GitHub repository. Together, these materials support independent inspection and reproduction of the reported results.

This work is released as a preprint and has not undergone formal peer review.