Micro-framework for Agents: the new way to build a backend

import { capability, t } from '@ts-atlas/core/runtime';

const Line = t.object({ sku: t.string, quantity: t.int, unitPriceCents: t.int });
const ada = { id: 'c1', roles: [] };

export default capability({
  name: 'orders',
  intent: 'Customers place orders for themselves and cancel their own, at most once. The customer is the actor, never the payload.',
  owns: {
    orders: t.object({
      orderId: t.string, customerId: t.string, status: t.enum('placed', 'cancelled'), lines: t.array(Line),
      totalCents: t.int, placedAt: t.string, cancelReason: t.nullable(t.string),
    }),
  },
  emits: { OrderPlaced: t.object({ orderId: t.string, customerId: t.string, lines: t.array(Line), totalCents: t.int }) },
})
  .command('PlaceOrder', {
    access: 'user',
    input: t.object({ orderId: t.string, lines: t.array(Line) }),
    reads: { existing: { from: 'orders', key: (input) => input.orderId } },
    decide({ input, state, now, actor }, d) {
      if (state.existing !== null) return d.reject('order-exists', { orderId: input.orderId });
      if (input.lines.length === 0) return d.reject('order-empty');
      const totalCents = input.lines.reduce((sum, line) => sum + line.quantity * line.unitPriceCents, 0);
      const order = { ...input, customerId: actor.id, totalCents };
      return d.accept({
        write: [d.write('orders', input.orderId, { ...order, status: 'placed', placedAt: now, cancelReason: null })],
        emit: [d.fact('OrderPlaced', order)],
      });
    },
    examples: [
      { name: 'rejects an anonymous caller', actor: null, input: { orderId: 'o1', lines: [] }, expect: { rejects: 'unauthenticated' } },
      { name: 'rejects an empty order', actor: ada, input: { orderId: 'o1', lines: [] }, expect: { rejects: 'order-empty' } },
      // …
    ],
  });