fix(hal): return DispenseResult from IPC dispense handler

The hal:dispense IPC handler in main.ts did not return the result of
dispenseCash(), causing the state machine guard to crash on undefined
output. This left the UI stuck on "Dispensing cash..." after successful
dispense.

- hal-service.ts: return DispenseResult instead of void/throwing
- main.ts: add missing return in IPC handler
- machine.ts: defensive guard (?. instead of .) as safety net

Bug found with the aid of Seoyoung at Trece Cielos.

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

apps/machine/electron/hal-service.ts

@@ -34,13 +34,19 @@ export interface ValidatorCallbacks {
   onError: (error: string) => void
 }
 
+export interface DispenseResult {
+  bills: { denomination: number; dispensed: number; rejected: number }[]
+  dispensed: boolean
+  error?: string
+}
+
 export interface HalInstance {
   connectValidator: (callbacks: ValidatorCallbacks) => void
   enableValidator: () => void
   disableValidator: () => void
   stackBill: () => void
   rejectBill: () => void
-  dispenseCash: (amounts: { denomination: number; count: number }[]) => Promise<void>
+  dispenseCash: (amounts: { denomination: number; count: number }[]) => Promise<DispenseResult>
   getInventory: () => Record<number, number>
   cleanup: () => Promise<void>
 }
@@ -139,14 +145,22 @@ export async function initializeHal(config: HalConfig): Promise<HalInstance> {
     stackBill: () => validator.stack(),
     rejectBill: () => validator.reject(),
 
-    dispenseCash: async (amounts) => {
+    dispenseCash: async (amounts): Promise<DispenseResult> => {
       console.log('[HAL] Dispensing:', amounts)
 
       const notes: number[] = new Array(cassetteDenominations.length).fill(0)
       for (const { denomination, count } of amounts) {
         const idx = cassetteDenominations.indexOf(denomination)
         if (idx === -1) {
-          throw new Error(`No cassette loaded with denomination: ${denomination}`)
+          return {
+            bills: amounts.map((a) => ({
+              denomination: a.denomination,
+              dispensed: 0,
+              rejected: 0,
+            })),
+            dispensed: false,
+            error: `No cassette loaded with denomination: ${denomination}`,
+          }
         }
         notes[idx] = count
       }
@@ -161,12 +175,27 @@ export async function initializeHal(config: HalConfig): Promise<HalInstance> {
         }
       }
 
+      // Build per-denomination result
+      const bills = amounts.map((a, i) => ({
+        denomination: a.denomination,
+        dispensed: result.value[i]?.dispensed ?? 0,
+        rejected: result.value[i]?.rejected ?? 0,
+      }))
+
+      const totalRequested = amounts.reduce((s, a) => s + a.count, 0)
+      const totalDispensed = bills.reduce((s, b) => s + b.dispensed, 0)
+
       if (result.error) {
-        throw result.error
+        return { bills, dispensed: false, error: result.error.message }
       }
 
-      await dispenser.waitForBillsRemoved()
-      console.log('[HAL] Bills removed by customer')
+      // Wait for customer to take bills
+      if (totalDispensed > 0) {
+        await dispenser.waitForBillsRemoved()
+        console.log('[HAL] Bills removed by customer')
+      }
+
+      return { bills, dispensed: totalRequested === totalDispensed }
     },
 
     getInventory: () => ({ ...inventory }),