Fix WebUI rolling-window and buffer-wrap display bugs

Replace fragile zoomGuard boolean with userInteracting flag so that
programmatic scale updates (rolling window, resize, fit) never lock
p.xRange.  Only genuine mouse drag or scroll-wheel events on the uPlot
canvas set userInteracting=true and allow onZoom to freeze the view.

Also move stale-xRange detection out of the needsRedraw gate so that a
plot whose circular buffer has scrolled past a frozen zoom range
automatically returns to rolling-window mode every frame, fixing the
second bug where data disappeared as the buffer wrapped.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Client/WebUI/hub.go

@@ -90,6 +90,7 @@ type Hub struct {
 	mu       sync.RWMutex
 	signals  []SignalInfo
 	configJS []byte // cached JSON config message
+	configSeq uint64 // incremented on every UpdateConfig call
 
 	clients     map[*wsClient]bool
 	register    chan *wsClient
@@ -97,16 +98,26 @@ type Hub struct {
 	broadcastCh chan []byte // all sends go through Run() to avoid races on c.send
 
 	dataCh chan DataSample // incoming samples from UDP goroutine
+
+	// Time-signal calibration: only accessed from the Run() goroutine.
+	// For temporal-array signals (TimeMode=FirstSample/LastSample), the
+	// MARTe2 Time signal value (uint32 microseconds from start) is used as
+	// the timing anchor.  We calibrate a per-signal wall-clock offset once
+	// on the first data packet so that subsequent packets are stamped purely
+	// from the embedded timer value → perfect continuity, no jitter gaps.
+	timeSigCalib    map[string]float64 // key=time-signal name, value=wallTime-timerSecs offset
+	configSeqAtCalib uint64             // configSeq value when timeSigCalib was last reset
 }
 
 // NewHub creates an initialised Hub.
 func NewHub() *Hub {
 	return &Hub{
-		clients:     make(map[*wsClient]bool),
-		register:    make(chan *wsClient, 8),
-		unregister:  make(chan *wsClient, 8),
-		broadcastCh: make(chan []byte, 64),
-		dataCh:      make(chan DataSample, 256),
+		clients:      make(map[*wsClient]bool),
+		register:     make(chan *wsClient, 8),
+		unregister:   make(chan *wsClient, 8),
+		broadcastCh:  make(chan []byte, 64),
+		dataCh:       make(chan DataSample, 256),
+		timeSigCalib: make(map[string]float64),
 	}
 }
 
@@ -123,6 +134,7 @@ func (h *Hub) UpdateConfig(sigs []SignalInfo) {
 	h.mu.Lock()
 	h.signals = sigs
 	h.configJS = msg
+	h.configSeq++
 	h.mu.Unlock()
 
 	h.broadcast(msg)
@@ -256,10 +268,11 @@ type dataMsg struct {
 //
 // Three cases are handled:
 //
-//  1. Temporal array (NumElements > 1, TimeMode != PacketTime):
+//  1. Temporal array (NumElements > 1, TimeMode == FirstSample or LastSample):
 //     The N samples in each packet represent a contiguous time burst at SamplingRate.
-//     Wall arrival time is treated as the timestamp of the last sample; earlier
-//     samples are reconstructed as t[k] = wallT - (N-1-k)/SamplingRate.
+//     The embedded TimeSignal value (uint32 microseconds) is used as the timing
+//     anchor for each burst.  A wall-clock offset is calibrated once on the first
+//     packet so that abs-time stays consistent with other signals.
 //     The full expanded stream is decimated to maxBatchPoints if needed.
 //
 //  2. Scalar signal (NumElements == 1):
@@ -273,32 +286,83 @@ func (h *Hub) buildDataMessage(batch []DataSample, sigs []SignalInfo) []byte {
 		return nil
 	}
 
+	// Reset time-signal calibration whenever the config has changed.
+	h.mu.RLock()
+	seq := h.configSeq
+	h.mu.RUnlock()
+	if seq != h.configSeqAtCalib {
+		h.configSeqAtCalib = seq
+		h.timeSigCalib = make(map[string]float64)
+	}
+
 	out := make(map[string]sigData, len(sigs)*2)
 
 	for _, sig := range sigs {
 		n := sig.NumElements()
-		isTemporal := n > 1 && sig.TimeMode != 0
+		isTemporal := n > 1 && (sig.TimeMode == TimeModeFirstSample || sig.TimeMode == TimeModeLastSample)
 
 		switch {
 		case isTemporal:
-			// Expand each packet's N samples into individual time-stamped points.
-			allT := make([]float64, 0, len(batch)*n)
-			allV := make([]float64, 0, len(batch)*n)
+			// Resolve time signal (scalar that gives the anchor time in microseconds).
+			hasTimeSig := sig.TimeSignalIdx != NoTimeSignal && int(sig.TimeSignalIdx) < len(sigs)
+			var timeSigName string
+			if hasTimeSig {
+				timeSigName = sigs[sig.TimeSignalIdx].Name
+			}
 
 			dt := 0.0
 			if sig.SamplingRate > 0 {
 				dt = 1.0 / sig.SamplingRate
 			}
 
+			// Expand each packet's N samples into individual time-stamped points.
+			allT := make([]float64, 0, len(batch)*n)
+			allV := make([]float64, 0, len(batch)*n)
+
 			for _, s := range batch {
 				vals, ok := s.Values[sig.Name]
 				if !ok || len(vals) < n {
 					continue
 				}
-				// wallT ≈ arrival time of the packet ≈ timestamp of the last sample.
-				wallT := float64(s.WallTime.UnixNano()) / 1e9
+
+				// Compute the anchor timestamp for this burst.
+				// Prefer the embedded time-signal value (microseconds) so that
+				// consecutive bursts are perfectly contiguous regardless of jitter.
+				var anchorTime float64
+				anchorIsFirstSample := (sig.TimeMode == TimeModeFirstSample)
+
+				if hasTimeSig {
+					tVals, tOk := s.Values[timeSigName]
+					if tOk && len(tVals) >= 1 {
+						// Time signal is uint32 microseconds from system start.
+						timerS := tVals[0] * 1e-6
+						wallT := float64(s.WallTime.UnixNano()) / 1e9
+
+						// Calibrate the wall-clock offset once per session so that
+						// anchor times can be expressed as absolute Unix timestamps.
+						if _, exists := h.timeSigCalib[timeSigName]; !exists {
+							h.timeSigCalib[timeSigName] = wallT - timerS
+						}
+						anchorTime = h.timeSigCalib[timeSigName] + timerS
+					} else {
+						// Time signal missing in this packet – fall back to wall clock.
+						anchorTime = float64(s.WallTime.UnixNano()) / 1e9
+						anchorIsFirstSample = false // wallT = last sample
+					}
+				} else {
+					// No time signal configured – use wall arrival as last-sample anchor.
+					anchorTime = float64(s.WallTime.UnixNano()) / 1e9
+					anchorIsFirstSample = false
+				}
+
 				for k := 0; k < n; k++ {
-					allT = append(allT, wallT-float64(n-1-k)*dt)
+					var t float64
+					if anchorIsFirstSample {
+						t = anchorTime + float64(k)*dt
+					} else {
+						t = anchorTime - float64(n-1-k)*dt
+					}
+					allT = append(allT, t)
 					allV = append(allV, vals[k])
 				}
 			}