staticaddr/deposit: handle loop-in htlc timeout

Keep deposits locked when the server publishes the loop-in HTLC
without paying the invoice.

This lets the client sweep through the HTLC timeout path instead
of making the same outputs available for another action.

staticaddr/deposit/fsm.go

@@ -353,6 +353,11 @@ func (f *FSM) DepositStatesV0() fsm.States {
 				// still pending, we publish the expiry sweep.
 				OnExpiry: PublishExpirySweep,
 
+				// If the server publishes the HTLC without
+				// paying us, we need to keep the deposit locked
+				// until the HTLC timeout path can be swept.
+				OnSweepingHtlcTimeout: SweepHtlcTimeout,
+
 				OnLoopInInitiated: LoopingIn,
 
 				OnRecover:   LoopingIn,

staticaddr/deposit/fsm_test.go

@@ -0,0 +1,52 @@
+package deposit
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/wire"
+	"github.com/lightninglabs/loop/fsm"
+	"github.com/lightninglabs/loop/staticaddr/script"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+// TestLoopingInTransitionsToSweepHtlcTimeout verifies that a deposit selected
+// by a loop-in can be moved into the timeout sweep state if the server confirms
+// the HTLC without paying the invoice.
+func TestLoopingInTransitionsToSweepHtlcTimeout(t *testing.T) {
+	t.Parallel()
+
+	outpoint := wire.OutPoint{
+		Hash:  chainhash.Hash{9},
+		Index: 9,
+	}
+	deposit := &Deposit{
+		OutPoint: outpoint,
+	}
+	deposit.SetState(LoopingIn)
+
+	store := new(mockStore)
+	store.On(
+		"UpdateDeposit", mock.Anything, mock.Anything,
+	).Return(nil).Once()
+
+	depositFSM := &FSM{
+		cfg: &ManagerConfig{
+			Store: store,
+		},
+		deposit: deposit,
+		params:  &script.Parameters{Expiry: 1},
+	}
+	depositFSM.StateMachine = fsm.NewStateMachineWithState(
+		depositFSM.DepositStatesV0(), LoopingIn, DefaultObserverSize,
+	)
+	depositFSM.ActionEntryFunc = depositFSM.updateDeposit
+
+	err := depositFSM.SendEvent(
+		t.Context(), OnSweepingHtlcTimeout, nil,
+	)
+	require.NoError(t, err)
+	require.Equal(t, SweepHtlcTimeout, deposit.GetState())
+	store.AssertExpectations(t)
+}