Meter every paid call.

import type { AccessContext, MeterReserveInput } from "@usagekit/core";
import { loadBudgetsView } from "@usagekit/views";
import { callProvider, meter } from "./server";

export async function meteredCall(
  access: AccessContext,
  input: MeterReserveInput,
) {
  const reserved = await meter.reserve(input);
  if (reserved.outcome !== "reserved") return reserved;
  if (reserved.replayed) return reserved; // A replay never dispatches.

  const { namespace, principal } = input.scope;
  const ref = { namespace, principal, operationId: input.operationId };
  const grant = await meter.markDispatchIntent({
    ...ref,
    commandId: `dispatch:${ref.operationId}`,
    expectedVersion: reserved.operation.version,
    holder: "api-worker",
    leaseTtlMs: 30_000,
  });
  if ("outcome" in grant || !grant.granted) return grant;
  const receipt = await callProvider(input); // The only provider call.

  const settled = await meter.settle({
    ...ref,
    commandId: `settle:${ref.operationId}`,
    expectedVersion: grant.operation.version,
    authority: { kind: "lease", leaseId: grant.lease.leaseId },
    receipt, // An unknown cost settles as pending and stays reserved.
  });
  if (settled.outcome !== "settled") return settled;

  return loadBudgetsView(meter, access, {
    scope: input.scope,
    surface: input.surface,
    units: ["cents"],
    crossings: settled.alerts,
  });
}