fix(machine): decrement cassettes by position, not denomination, on cash-out

recordTransaction() updated cassette counts with WHERE denomination = ?,
but the v9 migration made position the PK precisely so duplicate
denominations across bays are legal (and the HAL dispense path already
returns authoritative per-position results). On any machine with two
bays of the same denomination, a single dispense drained every matching
bay row — silently corrupting inventory, the operator cassette-state
publish, and out-of-money gating.

- cassettes branch: decrement by c.position
- mock-only fallback (no per-bay results): drain matching bays greedily
  in position order, mirroring the dispenser's own fill order
- regression tests with a duplicate-denomination layout (3 of 5 fail
  against the old code)

Found during the dev-branch architecture review.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/machine/electron/state-store.ts

@@ -982,8 +982,11 @@ export function recordTransaction(tx: TransactionInput): void {
   const insertCassetteBill = db.prepare(
     'INSERT INTO cassette_bills (txid, name, position, denomination, provisioned, dispensed, rejected) VALUES (?, ?, ?, ?, ?, ?, ?)'
   )
-  const updateCassette = db.prepare(
-    'UPDATE cassettes SET count = MAX(0, count + ?) WHERE denomination = ?'
+  const updateCassetteByPosition = db.prepare(
+    'UPDATE cassettes SET count = MAX(0, count + ?) WHERE position = ?'
+  )
+  const selectBaysByDenom = db.prepare(
+    'SELECT position, count FROM cassettes WHERE denomination = ? ORDER BY position'
   )
   const updateCashboxStmt = db.prepare(
     'UPDATE cashbox SET total_bills = total_bills + ?, total_fiat_cents = total_fiat_cents + ? WHERE id = 1'
@@ -1024,17 +1027,33 @@ export function recordTransaction(tx: TransactionInput): void {
     }
 
     if (t.type === 'cash_out') {
-      // Decrement cassettes by ACTUALLY dispensed count (not requested)
+      // Decrement cassettes by ACTUALLY dispensed count (not requested).
+      // Position is the addressable unit (v9): duplicate denominations
+      // across bays are legal, so a denomination-keyed UPDATE would
+      // decrement every matching bay.
       if (t.cassettes) {
         for (const c of t.cassettes) {
           if (c.dispensed > 0) {
-            updateCassette.run(-c.dispensed, c.denomination)
+            updateCassetteByPosition.run(-c.dispensed, c.position)
           }
         }
       } else {
-        // Fallback: use bill counts (backward compat for mocks without cassette data)
+        // Fallback: per-denomination bill counts (mocks without per-bay
+        // results). Drain matching bays greedily in position order —
+        // the dispenser's own fill order.
         for (const bill of t.bills) {
-          updateCassette.run(-bill.count, bill.denomination)
+          let remaining = bill.count
+          const bays = selectBaysByDenom.all(bill.denomination) as {
+            position: number
+            count: number
+          }[]
+          for (const bay of bays) {
+            if (remaining <= 0) break
+            const take = Math.min(remaining, bay.count)
+            if (take <= 0) continue
+            updateCassetteByPosition.run(-take, bay.position)
+            remaining -= take
+          }
         }
       }
     }