feat(state-machine): fetch balance with exchange rate on cash-in

Add getRateAndBalance actor that fetches exchange rate and available
balance in parallel during cash-in flow. Add generateLnurlWithdraw
service type for LNURL-withdraw support.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

packages/state-machine/src/machine.ts

@@ -68,6 +68,17 @@ export function createATMMachine(services: Partial<ATMServices> = {}) {
         }
         return services.getExchangeRate(input)
       }),
+      // Fetch both exchange rate and available balance in parallel for cash-in
+      getRateAndBalance: fromPromise(async ({ input }: { input: string }) => {
+        if (!services.getExchangeRate) {
+          throw new Error('getExchangeRate service not provided')
+        }
+        const [exchangeRate, availableBalance] = await Promise.all([
+          services.getExchangeRate(input),
+          services.getAvailableBalance ? services.getAvailableBalance() : Promise.resolve(0),
+        ])
+        return { exchangeRate, availableBalance }
+      }),
       generateNoffer: fromPromise(async () => {
         if (!services.generateNoffer) {
           throw new Error('generateNoffer service not provided')
@@ -363,12 +374,13 @@ export function createATMMachine(services: Partial<ATMServices> = {}) {
         states: {
           fetchingRate: {
             invoke: {
-              src: 'getExchangeRate',
+              src: 'getRateAndBalance',
               input: ({ context }) => context.currency,
               onDone: {
                 target: 'insertingBills',
                 actions: assign({
-                  exchangeRate: ({ event }) => event.output,
+                  exchangeRate: ({ event }) => event.output.exchangeRate,
+                  availableBalance: ({ event }) => event.output.availableBalance,
                 }),
               },
               onError: {

packages/state-machine/src/types.ts

@@ -33,6 +33,8 @@ export interface ATMContext {
   exchangeRate: number
   /** Fee percentage (0.02 = 2%) */
   feePercent: number
+  /** ATM's available balance in sats (for limiting cash-in transactions) */
+  availableBalance: number
 
   // Payment
   /** BOLT11 invoice for payment */
@@ -128,6 +130,7 @@ export const initialContext: ATMContext = {
   currency: 'USD',
   exchangeRate: 0,
   feePercent: 0.02,
+  availableBalance: 0,
   invoice: null,
   clinkOffer: null,
   nofferString: null,
@@ -167,6 +170,8 @@ export interface ATMServices {
   dispenseCash: (amounts: { denomination: number; count: number }[]) => Promise<void>
   /** Get current exchange rate */
   getExchangeRate: (currency: string) => Promise<number>
+  /** Get ATM's available balance in sats (for limiting cash-in transactions) */
+  getAvailableBalance: () => Promise<number>
   /** Generate noffer string for cash-out (static payment code) */
   generateNoffer: () => Promise<string>
   /**