/**
 * Shared JSON-RPC utility for holdout helpers.
 *
 * Exported from one place so wallet.ts, assertions.ts, and future helpers
 * share a single implementation rather than embedding the same fetch +
 * error-check block in each file.
 */
export async function rpcCall(rpcUrl: string, method: string, params: unknown[]): Promise<unknown> {
  const resp = await fetch(rpcUrl, {
    method: 'POST',
    headers: { 'content-type': 'application/json' },
    body: JSON.stringify({ jsonrpc: '2.0', id: Date.now(), method, params }),
  });
  const payload = await resp.json();
  if (payload.error) throw new Error(`RPC ${method}: ${payload.error.message}`);
  return payload.result;
}