Add synthetic array (waveform) DSP support + UX improvements

Adds full array/waveform support through the synthetic DSP engine: a
dsp.Sample value model (scalar or []float64), array ops (index, slice,
sum, mean, min, max, length, fft) with an in-tree radix-2 FFT, and static
type propagation (OpOutputType) that the editor mirrors to colour wires by
data type and flag invalid wirings. Stateful filters and lua stay
scalar-only. Adds a waveform plot mode (x-vs-index trace).

Also: errored-node hover reasons, S/N add-signal/add-node HUD shortcuts in
the synthetic editor, and view-mode widgets that blend with the canvas
background (chrome kept in edit mode).

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

internal/datasource/synthetic/synthetic.go

@@ -13,6 +13,7 @@ import (
 
 	"github.com/uopi/uopi/internal/broker"
 	"github.com/uopi/uopi/internal/datasource"
+	"github.com/uopi/uopi/internal/dsp"
 )
 
 const definitionsFile = "synthetic.json"
@@ -78,7 +79,7 @@ func (s *Synthetic) ListSignals(_ context.Context) ([]datasource.Metadata, error
 
 	out := make([]datasource.Metadata, 0, len(s.signals))
 	for _, st := range s.signals {
-		out = append(out, defToMetadata(st.def))
+		out = append(out, defToMetadata(st.def, outTypeOf(st)))
 	}
 	return out, nil
 }
@@ -93,7 +94,7 @@ func (s *Synthetic) FilteredMetadata(keep func(SignalDef) bool) []datasource.Met
 	out := make([]datasource.Metadata, 0, len(s.signals))
 	for _, st := range s.signals {
 		if keep(st.def) {
-			out = append(out, defToMetadata(st.def))
+			out = append(out, defToMetadata(st.def, outTypeOf(st)))
 		}
 	}
 	return out
@@ -108,7 +109,7 @@ func (s *Synthetic) GetMetadata(_ context.Context, signal string) (datasource.Me
 	if !ok {
 		return datasource.Metadata{}, datasource.ErrNotFound
 	}
-	return defToMetadata(st.def), nil
+	return defToMetadata(st.def, outTypeOf(st)), nil
 }
 
 // Subscribe registers ch to receive computed values for the named signal.
@@ -138,7 +139,7 @@ func (s *Synthetic) Subscribe(ctx context.Context, signal string, ch chan<- data
 		defer cancel()
 
 		// Latest value and timestamp per source node id.
-		latest := make(map[string]float64, len(refs))
+		latest := make(map[string]dsp.Sample, len(refs))
 		latestTs := make([]time.Time, len(refs))
 		ready := make([]bool, len(refs))
 
@@ -163,7 +164,7 @@ func (s *Synthetic) Subscribe(ctx context.Context, signal string, ch chan<- data
 							if !ok {
 								return
 							}
-							val := toFloat64(u.Value.Data)
+							val := toSample(u.Value.Data)
 							select {
 							case updateCh <- indexedUpdate{idx: idx, val: val, ts: u.Value.Timestamp}:
 							default:
@@ -224,7 +225,7 @@ func (s *Synthetic) Subscribe(ctx context.Context, signal string, ch chan<- data
 					return
 				}
 
-				result, err := cur.rg.eval(latest)
+				result, err := cur.rg.evalSample(latest)
 				if err != nil {
 					s.log.Warn("synthetic: pipeline error", "signal", signal, "err", err)
 					continue
@@ -232,7 +233,7 @@ func (s *Synthetic) Subscribe(ctx context.Context, signal string, ch chan<- data
 
 				v := datasource.Value{
 					Timestamp: outTs,
-					Data:      result,
+					Data:      result.AsAny(),
 					Quality:   datasource.QualityGood,
 				}
 				select {
@@ -421,11 +422,17 @@ func (s *Synthetic) startSignal(def SignalDef) error {
 	return nil
 }
 
-// defToMetadata converts a SignalDef into a datasource.Metadata.
-func defToMetadata(def SignalDef) datasource.Metadata {
+// defToMetadata converts a SignalDef into a datasource.Metadata. outType is the
+// compiled graph's best-effort output type; an array output is reported as a
+// waveform (TypeFloat64Array) so widgets can pick a compatible view.
+func defToMetadata(def SignalDef, outType dsp.ValType) datasource.Metadata {
+	dt := datasource.TypeFloat64
+	if outType == dsp.ValArray {
+		dt = datasource.TypeFloat64Array
+	}
 	return datasource.Metadata{
 		Name:        def.Name,
-		Type:        datasource.TypeFloat64,
+		Type:        dt,
 		Unit:        def.Meta.Unit,
 		Description: def.Meta.Description,
 		DisplayLow:  def.Meta.DisplayLow,
@@ -434,7 +441,38 @@ func defToMetadata(def SignalDef) datasource.Metadata {
 	}
 }
 
-// toFloat64 coerces any numeric value from a datasource.Value.Data to float64.
+// outTypeOf returns the compiled output type for a signal state, or unknown.
+func outTypeOf(st *signalState) dsp.ValType {
+	if st == nil || st.rg == nil {
+		return dsp.ValUnknown
+	}
+	return st.rg.outType
+}
+
+// toSample coerces a datasource.Value.Data into a dsp.Sample: arrays become
+// array Samples (waveforms), everything else a scalar Sample.
+func toSample(v any) dsp.Sample {
+	switch val := v.(type) {
+	case []float64:
+		return dsp.Array(val)
+	case []float32:
+		out := make([]float64, len(val))
+		for i, e := range val {
+			out[i] = float64(e)
+		}
+		return dsp.Array(out)
+	case []int:
+		out := make([]float64, len(val))
+		for i, e := range val {
+			out[i] = float64(e)
+		}
+		return dsp.Array(out)
+	default:
+		return dsp.Scalar(toFloat64(v))
+	}
+}
+
+// toFloat64 coerces any numeric scalar value from a datasource.Value.Data to float64.
 func toFloat64(v any) float64 {
 	switch val := v.(type) {
 	case float64:
@@ -460,6 +498,6 @@ func toFloat64(v any) float64 {
 // indexedUpdate carries a value from one upstream goroutine to the pipeline runner.
 type indexedUpdate struct {
 	idx int
-	val float64
+	val dsp.Sample
 	ts  time.Time
 }