fix: make slot payout and stake resolution one durable save

1 files changed, 38 insertions, 0 deletions

diff --git a/internal/casino/paycredits_atomic_test.go b/internal/casino/paycredits_atomic_test.go
new file mode 100644
index 0000000..b08415e
--- /dev/null
+++ b/internal/casino/paycredits_atomic_test.go
@@ -0,0 +1,38 @@
+package casino
+
+import "testing"
+
+// recordingWallet records the stake IDs passed to PayCredits so a winning
+// spin's atomicity can be asserted directly.
+type recordingWallet struct {
+	testWallet
+	payStakes []string
+}
+
+func (w *recordingWallet) PayCredits(amount int, stakeIDs ...string) error {
+	w.payStakes = append(w.payStakes, stakeIDs...)
+	return w.testWallet.PayCredits(amount, stakeIDs...)
+}
+
+// TestWinningSpinConsumesStakeInPayoutSave: a winning paid spin must pass its
+// triggering stake to the SAME PayCredits call, so the credit and the stake
+// consumption are one durable save. Resolving the stake in a separate later
+// call leaves a crash window in which the payout is durable but the stake is
+// still pending — startup would then refund it on top of the win.
+func TestWinningSpinConsumesStakeInPayoutSave(t *testing.T) {
+	m := newMachine(1, MachineConfig{ID: "slots", Game: GameSlots}, newTestRand())
+	w := &recordingWallet{testWallet: testWallet{credits: 100}}
+	m.join("alice")
+	m.beginSpinLocked(10, w, "", "")
+	wagerID := m.stakeID
+
+	m.spin = &SlotSpin{Payout: 25}
+	m.finishSpin()
+
+	if len(w.payStakes) != 1 || w.payStakes[0] != wagerID {
+		t.Fatalf("winning spin passed stakes %v to PayCredits; want [%q] (one atomic payout+resolve)", w.payStakes, wagerID)
+	}
+	if len(w.open) != 0 {
+		t.Fatalf("winning spin left %d stake(s) pending: %+v", len(w.open), w.open)
+	}
+}