Expense Approval

1SUBMITTED --------[submit_expense]-------> PENDING_APPROVAL
2PENDING_APPROVAL ------[approve]---------> APPROVED (terminal)
3PENDING_APPROVAL -------[reject]---------> REJECTED (terminal)

1import { LoopBuilder } from "@loop-engine/sdk";
2 
3"cmt">// The human-only guard is the load-bearing governance rule.
4const expenseApproval = LoopBuilder
5  .create("expense.approval", "finance")
6  .description("Expense report approval")
7  .state("SUBMITTED")
8  .state("PENDING_APPROVAL")
9  .state("APPROVED", { isTerminal: true })
10  .state("REJECTED", { isTerminal: true })
11  .initialState("SUBMITTED")
12  .transition({
13    id: "submit_expense",
14    from: "SUBMITTED",
15    to: "PENDING_APPROVAL",
16    actors: ["human", "automation"]
17  })
18  .transition({
19    id: "approve",
20    from: "PENDING_APPROVAL",
21    to: "APPROVED",
22    actors: ["human"],
23    guards: [
24      {
25        id: "human-only" as never,
26        description: "Only a human approver can approve expenses",
27        severity: "hard",
28        evaluatedBy: "runtime"
29      }
30    ]
31  })
32  .transition({ id: "reject", from: "PENDING_APPROVAL", to: "REJECTED", actors: ["human"] })
33  .build();

1{
2  type: "loop.transition.executed",
3  loopId: "expense.approval",
4  aggregateId: "EXP-2026-001",
5  transitionId: "approve",
6  fromState: "PENDING_APPROVAL",
7  toState: "APPROVED",
8  actor: { type: "human", id: "manager@acme.com" },
9  occurredAt: "2026-03-13T12:05:10.991Z"
10}

1cd loop-examples/expense-approval
2pnpm install
3pnpm dev