Safety Invariants for Agents Orchestrating Irreversible State Transitions: A Four-Dimensional Formalism Evaluated on Public Ledgers

Autonomous agents are increasingly asked to produce irreversible effects on external systems - transferring funds, writing to durable storage, actuating hardware. Existing agent frameworks (ReAct, Reflexion, MCP) optimize task success on benchmarks and give little attention to the safety of irreversible side-effects. We formalize one such setting, movement of value across public ledgers, as state transitions in a four-dimensional space indexed by (wallet, chain, address, protocol), and use that formalism to state and prove a guarantee we call execution fidelity: under a fault model admitting planner mis-mapping, ambiguous outcomes, retries, at-least-once delivery, and delegated non-human callers, a session's realized effect on the ledger is either nothing at all or exactly the transition that was rendered to the user, exactly once. The theorem deliberately does not claim that the rendered transition matches the user's intent - no runtime layer can decide that - but it confines that unbounded question to a single predicate over a finite object, which is what makes a preview a sufficient control rather than a formality. Seven safety invariants, derived from the fidelity condition rather than enumerated from experience, discharge the guarantee. Empirically, on a controlled N=60 adversarial suite the stack lifts pass rate by 74 percentage points over a naive-ReAct baseline on two write-aggressive backing models, but by only 3 points on a write-cautious one - evidence that single-model evaluations of agent safety stacks are close to unfalsifiable. The system is deployed; 108 production write operations across 8 chains back the failure taxonomy. Although the evaluation setting is public ledgers, the formalism and invariants apply to any probabilistic agent acting on irreversible external state.