Physics-Enforced Delegation: Governing Quantum Hardware Quality in Autonomous Agent Workflows

As autonomous systems and AI agents begin to access quantum cloud resources, existing agent governance frameworks enforce only budgets and delegation scope, not physical execution quality. We present a governance framework that enforces hardware fidelity constraints before permitting agent-mediated quantum computation. The framework extends cryptographic delegation chains with physics facets (coherence times, gate errors, readout errors, calibration freshness) that participate in the same monotonic narrowing invariant as budget and scope constraints. A cross-backend experiment on IBM Quantum hardware (ibm_fez, ibm_marrakesh, ibm_kingston) shows that governance correctly denies a backend where qubit T1 falls below the delegation threshold (39.1 µs vs. 80 µs minimum), while permitting backends meeting the constraint. A counterfactual experiment indicates a 5.2 percentage point Bell state fidelity gap between the denied and permitted backends (92.9% vs. 98.1%), widening to 7.7 points on a 4-qubit GHZ circuit. Governance overhead is 4.2 ms for policy evaluation and receipt signing. Ed25519-signed receipts bind each governance decision to the hardware calibration state at the moment of evaluation.