fix(cassettes): report a drained machine as drained

getInventory dropped zero-count bays, so a fully dispensed machine
returned an empty map — identical to a machine with no cassettes
configured. Every caller reads an empty map as "nothing known, ask the
hardware": reloadPersistedInventory skipped the update entirely, so the
last non-empty snapshot stuck and the public availability beacon went on
advertising bills that had already gone out the slot.

Zero-count bays are kept, so an empty map now means exactly one thing:
no cassettes are configured. Consumers already filter for > 0 before
offering a denomination. loadInventoryFromDb returns null when the DB
could not be asked at all (browser dev, failed IPC) so callers can still
tell "no answer" from an answer of "the bays are empty", and only the
former defers to HAL.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

apps/machine/electron/__tests__/state-store-transactions.test.ts

@@ -14,6 +14,7 @@ import { afterEach, beforeEach, describe, expect, it } from 'vitest'
 import {
   closeDatabase,
   getCashbox,
+  getInventory,
   initDatabase,
   loadCassettes,
   recordTransaction,
@@ -260,3 +261,64 @@ describe('state-store: recordTransaction manual_dispense inventory (#76)', () =>
     expect(countsByPosition()[2]).toBe(49)
   })
 })
+
+describe('state-store: getInventory represents a drained machine', () => {
+  it('keeps configured bays at zero rather than dropping them', () => {
+    recordTransaction({
+      ...TX_BASE,
+      txid: 'tx-drain-50s',
+      type: 'cash_out',
+      status: 'complete',
+      bills: [{ denomination: 50, count: 30 }],
+      cassettes: [
+        {
+          name: 'cassette3',
+          position: 3,
+          denomination: 50,
+          provisioned: 30,
+          dispensed: 30,
+          rejected: 0,
+        },
+      ],
+    })
+    // The $50 bay is empty but still configured. Dropping the key made this
+    // look like "no inventory known", and callers then fell back to a stale
+    // snapshot or to HAL.
+    expect(getInventory()).toEqual({ 20: 100, 50: 0 })
+  })
+
+  it('reports every bay at zero when the machine is fully drained', () => {
+    for (const [txid, position, denomination, count] of [
+      ['d1', 1, 20, 50],
+      ['d2', 2, 20, 50],
+      ['d3', 3, 50, 30],
+    ] as const) {
+      recordTransaction({
+        ...TX_BASE,
+        txid,
+        type: 'cash_out',
+        status: 'complete',
+        bills: [{ denomination, count }],
+        cassettes: [
+          {
+            name: `cassette${position}`,
+            position,
+            denomination,
+            provisioned: count,
+            dispensed: count,
+            rejected: 0,
+          },
+        ],
+      })
+    }
+    expect(getInventory()).toEqual({ 20: 0, 50: 0 })
+  })
+
+  it('returns an empty map only when no cassettes are configured', () => {
+    // A fresh DB with no bays at all — the one case that should read as
+    // "nothing known", so callers may legitimately defer to the hardware.
+    closeDatabase()
+    initDatabase(':memory:')
+    expect(getInventory()).toEqual({})
+  })
+})

apps/machine/electron/state-store.ts

@@ -874,9 +874,14 @@ export function getInventory(): Record<number, number> {
   const rows = loadCassettes()
   const inv: Record<number, number> = {}
   for (const row of rows) {
-    if (row.count > 0) {
-      inv[row.denomination] = (inv[row.denomination] ?? 0) + row.count
-    }
+    // Zero-count bays are KEPT. Dropping them made a drained machine
+    // indistinguishable from an unconfigured one, and every caller reads an
+    // empty map as "I don't know, ask the hardware" — so the last non-empty
+    // snapshot stuck and the availability beacon went on advertising bills
+    // that had already been dispensed. An empty map now means exactly one
+    // thing: no cassettes are configured. Consumers already filter for
+    // `> 0` before offering a denomination (CashOutView, machine.ts).
+    inv[row.denomination] = (inv[row.denomination] ?? 0) + row.count
   }
   return inv
 }

apps/machine/src/stores/atm.ts

@@ -161,10 +161,14 @@ async function handleManagementCommand(
 }
 
 /**
- * Load inventory from SQLite via IPC (Electron only).
- * Returns empty object in browser dev mode.
+ * Load inventory from SQLite via IPC.
+ *
+ * Returns `null` when the DB could not be asked at all — browser dev mode, or
+ * a failed IPC call — so callers can tell "no answer" from an answer of "the
+ * bays are empty". An empty map is a real, actionable reading: cassettes are
+ * configured and drained, or none are configured.
  */
-async function loadInventoryFromDb(): Promise<Record<number, number>> {
+async function loadInventoryFromDb(): Promise<Record<number, number> | null> {
   if (isElectron && window.electronAPI) {
     try {
       const inv = await window.electronAPI.getInventory()
@@ -174,7 +178,7 @@ async function loadInventoryFromDb(): Promise<Record<number, number>> {
       console.warn('[ATM] Failed to load inventory from DB:', e)
     }
   }
-  return {}
+  return null
 }
 
 /**
@@ -448,10 +452,12 @@ export const useAtmStore = defineStore('atm', () => {
 
   async function reloadPersistedInventory() {
     const inv = await loadInventoryFromDb()
-    if (Object.keys(inv).length > 0) {
-      persistedInventory.value = inv
-      console.log('[ATM] Persisted inventory updated:', inv)
-    }
+    // Only a failed read is ignored. An empty map used to be skipped too,
+    // which meant the last bill out of the machine never updated anything and
+    // the availability beacon kept advertising a full cassette.
+    if (inv === null) return
+    persistedInventory.value = inv
+    console.log('[ATM] Persisted inventory updated:', inv)
   }
 
   /** Detect Bitcoin network from a BOLT-11 invoice prefix (called once, persisted) */
@@ -1064,7 +1070,8 @@ export const useAtmStore = defineStore('atm', () => {
         }),
         getInventory: async () => {
           const fresh = await loadInventoryFromDb()
-          return Object.keys(fresh).length > 0 ? fresh : services.atmServices.getInventory()
+          // null == the DB could not be asked; an empty map is a real reading.
+          return fresh ?? services.atmServices.getInventory()
         },
       }
 
@@ -1327,7 +1334,8 @@ export const useAtmStore = defineStore('atm', () => {
         // If DB has inventory, use it; otherwise fall back to HAL
         getInventory: async () => {
           const fresh = await loadInventoryFromDb()
-          return Object.keys(fresh).length > 0 ? fresh : hal.atmServices.getInventory()
+          // null == the DB could not be asked; an empty map is a real reading.
+          return fresh ?? hal.atmServices.getInventory()
         },
       }
 
@@ -1611,9 +1619,11 @@ export const useAtmStore = defineStore('atm', () => {
           return await api.halDispense(amounts)
         },
         getInventory: async () => {
-          // Priority: DB inventory > HAL hardware inventory > empty
+          // Priority: DB inventory > HAL hardware inventory > empty. Only a
+          // null (unreadable) DB defers to HAL — a drained machine reports
+          // drained rather than borrowing the hardware's view.
           const fresh = await loadInventoryFromDb()
-          if (Object.keys(fresh).length > 0) return fresh
+          if (fresh !== null) return fresh
           // Fall back to HAL's cassette-based inventory
           try {
             const halInv = await api.halGetInventory()