refactor(hub): decode each agent response into a new struct

The WebSocket path reused sys.data, and CBOR leaves omitted fields
untouched, so stale values carried over (e.g. Details re-saved every
poll, SystemdServicesUpdated stuck true, old map entries kept).

sys.data is now set only by the regular update for alerts. Removes the
Wi-Fi-only workaround in UnmarshalResponse.

internal/hub/systems/system.go

@@ -153,6 +153,7 @@ func (sys *System) update() error {
 
 	// ensure deprecated fields from older agents are migrated to current fields
 	migrateDeprecatedFields(data, !sys.detailsFetched.Load())
+	sys.data = data
 
 	// create system records
 	_, err = sys.createRecords(data)
@@ -704,11 +705,9 @@ func (sys *System) ensureSSHTransport() error {
 }
 
 // fetchDataFromAgent attempts to fetch data from the agent, prioritizing WebSocket if available.
+// Each fetch decodes into a new struct: CBOR leaves fields the agent omits
+// untouched, and real-time and regular updates may fetch concurrently.
 func (sys *System) fetchDataFromAgent(options common.DataRequestOptions) (*system.CombinedData, error) {
-	if sys.data == nil {
-		sys.data = &system.CombinedData{}
-	}
-
 	if sys.WsConn != nil && sys.WsConn.IsConnected() {
 		wsData, err := sys.fetchDataViaWebSocket(options)
 		if err == nil {
@@ -744,11 +743,11 @@ func (sys *System) fetchDataViaWebSocket(options common.DataRequestOptions) (*sy
 	ctx, cancel := context.WithTimeout(context.Background(), wsDataRequestTimeout)
 	defer cancel()
 	wsTransport := transport.NewWebSocketTransport(sys.WsConn)
-	err := wsTransport.Request(ctx, common.GetData, options, sys.data)
-	if err != nil {
+	data := &system.CombinedData{}
+	if err := wsTransport.Request(ctx, common.GetData, options, data); err != nil {
 		return nil, err
 	}
-	return sys.data, nil
+	return data, nil
 }
 
 // FetchContainerInfoFromAgent fetches container info from the agent
@@ -810,9 +809,8 @@ func MakeStableHashId(strings ...string) string {
 }
 
 // fetchDataViaSSH handles fetching data using SSH.
-// This function encapsulates the original SSH logic.
-// It updates sys.data directly upon successful fetch.
 func (sys *System) fetchDataViaSSH(options common.DataRequestOptions) (*system.CombinedData, error) {
+	data := &system.CombinedData{}
 	err := sys.runSSHOperation(4*time.Second, 1, func(session *ssh.Session) (bool, error) {
 		stdout, err := session.StdoutPipe()
 		if err != nil {
@@ -823,7 +821,8 @@ func (sys *System) fetchDataViaSSH(options common.DataRequestOptions) (*system.C
 			return false, err
 		}
 
-		*sys.data = system.CombinedData{}
+		// reset in case of retry after a partial decode
+		*data = system.CombinedData{}
 
 		if sys.agentVersion.GTE(beszel.MinVersionAgentResponse) && stdinErr == nil {
 			req := common.HubRequest[any]{Action: common.GetData, Data: options}
@@ -832,7 +831,7 @@ func (sys *System) fetchDataViaSSH(options common.DataRequestOptions) (*system.C
 
 			var resp common.AgentResponse
 			if decErr := cbor.NewDecoder(stdout).Decode(&resp); decErr == nil && resp.SystemData != nil {
-				*sys.data = *resp.SystemData
+				*data = *resp.SystemData
 				if err := session.Wait(); err != nil {
 					return false, err
 				}
@@ -842,9 +841,9 @@ func (sys *System) fetchDataViaSSH(options common.DataRequestOptions) (*system.C
 
 		var decodeErr error
 		if sys.agentVersion.GTE(beszel.MinVersionCbor) {
-			decodeErr = cbor.NewDecoder(stdout).Decode(sys.data)
+			decodeErr = cbor.NewDecoder(stdout).Decode(data)
 		} else {
-			decodeErr = json.NewDecoder(stdout).Decode(sys.data)
+			decodeErr = json.NewDecoder(stdout).Decode(data)
 		}
 
 		if decodeErr != nil {
@@ -861,7 +860,7 @@ func (sys *System) fetchDataViaSSH(options common.DataRequestOptions) (*system.C
 		return nil, err
 	}
 
-	return sys.data, nil
+	return data, nil
 }
 
 // runSSHOperation establishes an SSH session and executes the provided operation.

internal/hub/systems/ws_fresh_data_test.go

@@ -0,0 +1,92 @@
+//go:build testing
+
+package systems
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/blang/semver"
+	"github.com/fxamacker/cbor/v2"
+	"github.com/henrygd/beszel/internal/common"
+	esystem "github.com/henrygd/beszel/internal/entities/system"
+	"github.com/henrygd/beszel/internal/hub/ws"
+	"github.com/lxzan/gws"
+	"github.com/stretchr/testify/require"
+)
+
+// sequenceDataClient answers each GetData request with the next queued payload.
+type sequenceDataClient struct {
+	gws.BuiltinEventHandler
+	responses chan esystem.CombinedData
+}
+
+func (c *sequenceDataClient) OnMessage(conn *gws.Conn, message *gws.Message) {
+	defer message.Close()
+	var req common.HubRequest[cbor.RawMessage]
+	if err := cbor.Unmarshal(message.Bytes(), &req); err != nil || req.Action != common.GetData {
+		return
+	}
+	data, _ := cbor.Marshal(<-c.responses)
+	response, _ := cbor.Marshal(common.AgentResponse{Id: req.Id, Data: data})
+	_ = conn.WriteMessage(gws.OpcodeBinary, response)
+}
+
+// Fields the agent omits must not carry over from a previous response.
+func TestFetchDataViaWebSocketDoesNotRetainOmittedFields(t *testing.T) {
+	connections := make(chan *ws.WsConn, 1)
+	upgrader := gws.NewUpgrader(&monitorSyncServer{}, nil)
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+		wsConn := ws.NewWsConnection(conn, semver.MustParse("0.20.0"))
+		conn.Session().Store("wsConn", wsConn)
+		connections <- wsConn
+		conn.ReadLoop()
+	}))
+	t.Cleanup(server.Close)
+
+	client := &sequenceDataClient{responses: make(chan esystem.CombinedData, 2)}
+	client.responses <- esystem.CombinedData{
+		Details:                &esystem.Details{Hostname: "host"},
+		SystemdServicesUpdated: true,
+		Stats:                  esystem.Stats{Batteries: map[string]uint8{"BAT0": 50, "BAT1": 60}},
+		Info:                   esystem.Info{WiFi: map[string]esystem.WiFi{"wlan0": {SSID: "home"}}},
+	}
+	client.responses <- esystem.CombinedData{
+		Stats: esystem.Stats{Batteries: map[string]uint8{"BAT0": 40}},
+	}
+	conn, _, err := gws.NewClient(client, &gws.ClientOption{Addr: "ws" + strings.TrimPrefix(server.URL, "http")})
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = conn.NetConn().Close() })
+	go conn.ReadLoop()
+
+	var sys *System
+	select {
+	case wsConn := <-connections:
+		sys = &System{WsConn: wsConn}
+	case <-time.After(3 * time.Second):
+		t.Fatal("websocket connection was not established")
+	}
+
+	first, err := sys.fetchDataFromAgent(common.DataRequestOptions{})
+	require.NoError(t, err)
+	require.NotNil(t, first.Details)
+	require.Len(t, first.Stats.Batteries, 2)
+
+	second, err := sys.fetchDataFromAgent(common.DataRequestOptions{})
+	require.NoError(t, err)
+	require.Nil(t, second.Details)
+	require.False(t, second.SystemdServicesUpdated)
+	require.Equal(t, map[string]uint8{"BAT0": 40}, second.Stats.Batteries)
+	require.Empty(t, second.Info.WiFi)
+
+	// the first result is not mutated by the second fetch
+	require.Len(t, first.Stats.Batteries, 2)
+}

internal/hub/transport/transport.go

@@ -35,14 +35,6 @@ func UnmarshalResponse(resp common.AgentResponse, action common.WebSocketAction,
 	}
 	// Try generic Data field first (0.19+)
 	if len(resp.Data) > 0 {
-		// Wi-Fi maps are complete snapshots. CBOR otherwise merges entries into
-		// reused destinations, retaining disconnected interfaces and old RSSI.
-		if action == common.GetData {
-			if data, ok := dest.(*system.CombinedData); ok {
-				data.Info.WiFi = nil
-				data.Stats.WiFi = nil
-			}
-		}
 		if err := cbor.Unmarshal(resp.Data, dest); err != nil {
 			return fmt.Errorf("failed to unmarshal generic response data: %w", err)
 		}

internal/hub/transport/wifi_test.go

@@ -1,43 +0,0 @@
-package transport
-
-import (
-	"github.com/fxamacker/cbor/v2"
-	"github.com/henrygd/beszel/internal/common"
-	"github.com/henrygd/beszel/internal/entities/system"
-	"github.com/stretchr/testify/require"
-	"testing"
-)
-
-func TestWiFiSequentialResponseSnapshots(t *testing.T) {
-	signal := -50.0
-	var decoded system.CombinedData
-	for _, snapshot := range []map[string]system.WiFi{
-		{"wlan0": {SSID: "home", Signal: &signal}, "wlan1": {Signal: &signal}},
-		{"wlan0": {SSID: "home"}}, {}, nil,
-		{"wlan1": {SSID: "new", Signal: &signal}},
-	} {
-		signals := make(map[string]int8)
-		for id, reading := range snapshot {
-			if reading.Signal != nil {
-				signals[id] = int8(*reading.Signal)
-			}
-		}
-		payload, err := cbor.Marshal(system.CombinedData{Info: system.Info{WiFi: snapshot}, Stats: system.Stats{WiFi: signals}})
-		require.NoError(t, err)
-		require.NoError(t, UnmarshalResponse(common.AgentResponse{Data: payload}, common.GetData, &decoded))
-		require.Len(t, decoded.Info.WiFi, len(snapshot))
-		require.Len(t, decoded.Stats.WiFi, len(signals))
-		for id, want := range snapshot {
-			require.Equal(t, want, decoded.Info.WiFi[id])
-		}
-		for id, want := range signals {
-			require.Equal(t, want, decoded.Stats.WiFi[id])
-		}
-	}
-	// An older generic-response agent may omit both fields entirely.
-	payload, err := cbor.Marshal(map[int]any{0: map[int]any{}, 1: map[int]any{}})
-	require.NoError(t, err)
-	require.NoError(t, UnmarshalResponse(common.AgentResponse{Data: payload}, common.GetData, &decoded))
-	require.Empty(t, decoded.Info.WiFi)
-	require.Empty(t, decoded.Stats.WiFi)
-}