@minsky-org/fsm-oracle

Ask an xstate machine "is this edge legal, and where does it land" without spawning an actor. The machine is the single source of truth for a lifecycle; every guard, every permission check, every UI affordance asks it the same way.

import { assertTransition } from "@minsky-org/fsm-oracle";

const next = assertTransition(orderMachine, current, { type: "SHIP" });
if (next === null) {
  return err("illegal transition");
}

Soundness condition

null means "the state value did not change". That is equivalent to "illegal" only if the machine has zero self-loops. A machine with a legal self-loop needs a different oracle, because a legal edge would report as a refusal.