cli: add command "loop stop"

* add StopDaemon RPC with permissions + REST binding
* expose `loop stop` CLI (with optional --wait) and wait logic
* pass daemon shutdown callback + unit test and regenerate docs/protos

loopd/daemon.go

@@ -746,6 +746,7 @@ func (d *Daemon) initialize(withMacaroonService bool) error {
 		withdrawalManager:    withdrawalManager,
 		staticLoopInManager:  staticLoopInManager,
 		assetClient:          d.assetClient,
+		stopDaemon:           d.Stop,
 	}
 
 	// Retrieve all currently existing swaps from the database.

loopd/swapclient_server.go

@@ -104,6 +104,9 @@ type swapClientServer struct {
 	nextSubscriberID     int
 	swapsLock            sync.Mutex
 	mainCtx              context.Context
+
+	// stopDaemon is invoked to trigger a graceful shutdown of the daemon.
+	stopDaemon func()
 }
 
 // LoopOut initiates a loop out swap with the given parameters. The call returns
@@ -1346,6 +1349,22 @@ func (s *swapClientServer) GetInfo(ctx context.Context,
 	}, nil
 }
 
+// StopDaemon triggers a graceful shutdown of the daemon process.
+func (s *swapClientServer) StopDaemon(ctx context.Context,
+	_ *looprpc.StopDaemonRequest) (*looprpc.StopDaemonResponse, error) {
+
+	// Ensure we have a shutdown handler to invoke.
+	if s.stopDaemon == nil {
+		return nil, status.Error(codes.Unimplemented,
+			"stop daemon not supported")
+	}
+
+	// Initiate the shutdown sequence.
+	s.stopDaemon()
+
+	return &looprpc.StopDaemonResponse{}, nil
+}
+
 // GetLiquidityParams gets our current liquidity manager's parameters.
 func (s *swapClientServer) GetLiquidityParams(_ context.Context,
 	_ *looprpc.GetLiquidityParamsRequest) (*looprpc.LiquidityParameters,

loopd/swapclient_server_test.go

@@ -261,6 +261,29 @@ func TestValidateLoopInRequest(t *testing.T) {
 	}
 }
 
+// TestSwapClientServerStopDaemon ensures that calling StopDaemon triggers the
+// daemon shutdown.
+func TestSwapClientServerStopDaemon(t *testing.T) {
+	t.Parallel()
+
+	// Prepare a server instance that tracks whether shutdown is requested.
+	var stopCalled bool
+	server := &swapClientServer{
+		stopDaemon: func() {
+			stopCalled = true
+		},
+	}
+
+	// Request the daemon to stop and assert the callback executed.
+	_, err := server.StopDaemon(
+		context.Background(), &looprpc.StopDaemonRequest{},
+	)
+	require.NoError(t, err)
+
+	// Ensure our shutdown callback executed.
+	require.True(t, stopCalled)
+}
+
 // TestValidateLoopOutRequest tests validation of loop out requests.
 func TestValidateLoopOutRequest(t *testing.T) {
 	tests := []struct {