fix(icom): say when a radio has no scope stream instead of drawing nothing

The CI-V trace settles it: the IC-7851 answers 27 10 01 with FB and 27 14 00
with its mode, but refuses 27 11 in BOTH shapes — it controls its scope over
CI-V and never streams it. Its last firmware is from 2016, older than the
waveform stream itself; Hamlib's caps claim otherwise, the radio is the
authority.

Rejected both ways is a permanent answer, so it is remembered and reported:
the panadapter says the radio does not send its scope, which is the one thing a
black rectangle could not say.

internal/cat/icomserial.go

@@ -93,15 +93,18 @@ type IcomSerial struct {
 	// leading main/sub selector byte (IC-7610/9700). scopeAmp is the latest
 	// reassembled sweep; scopeMu guards it (written by the scope goroutine, read
 	// via ScopeData from the binding goroutine).
-	dualScope  bool
-	scopeMu    sync.Mutex
-	scopeAmp   []byte
-	scopeLow   int64 // spectrum left-edge frequency (from the sweep's header frame)
-	scopeHigh  int64 // spectrum right-edge frequency
-	scopeSeq   int
-	scopeOn    bool
-	scopeFixed bool // true = fixed-span mode (tracked optimistically)
-	scopeSeen  bool // logged the first sweep's structure once (on-rig verification)
+	dualScope bool
+	// Set when the rig rejects the waveform-output command in both shapes: it has
+	// no stream to give, and asking again on every enable is noise.
+	scopeUnsupported bool
+	scopeMu          sync.Mutex
+	scopeAmp         []byte
+	scopeLow         int64 // spectrum left-edge frequency (from the sweep's header frame)
+	scopeHigh        int64 // spectrum right-edge frequency
+	scopeSeq         int
+	scopeOn          bool
+	scopeFixed       bool // true = fixed-span mode (tracked optimistically)
+	scopeSeen        bool // logged the first sweep's structure once (on-rig verification)
 
 	curFreq     int64     // last frequency read (for sideband choice)
 	curModeByte byte      // last raw Icom mode byte (for filter re-send)
@@ -1058,7 +1061,17 @@ func (b *IcomSerial) SetScope(on bool) error {
 	// the ONLY thing we switch off on disable, so the radio's own scope display is
 	// left exactly as the operator had it.
 	if err := b.execScope("data output", civ.SubScopeOn, boolByte(on)); err != nil {
-		applog.Printf("icom scope: output on=%v ack: %v — turn the CI-V trace on (Settings → CAT) and send the log", on, err)
+		applog.Printf("icom scope: output on=%v ack: %v", on, err)
+		// Rejected in both shapes = the command does not exist on this rig, which
+		// is a permanent answer and not a bad guess on our part. Remember it: the
+		// panel can then say so, and we stop asking a radio that has already
+		// said no.
+		if strings.Contains(err.Error(), "rejected") {
+			applog.Printf("icom scope: %s does not stream its scope over CI-V — control commands only", b.model)
+			b.scopeMu.Lock()
+			b.scopeUnsupported = true
+			b.scopeMu.Unlock()
+		}
 	}
 	b.scopeMu.Lock()
 	b.scopeOn = on
@@ -1302,7 +1315,8 @@ func (b *IcomSerial) ScopeData() ScopeSweep {
 	for i, v := range b.scopeAmp {
 		amp[i] = int(v)
 	}
-	return ScopeSweep{Amp: amp, Seq: b.scopeSeq, LowHz: b.scopeLow, HighHz: b.scopeHigh, Fixed: b.scopeFixed}
+	return ScopeSweep{Amp: amp, Seq: b.scopeSeq, LowHz: b.scopeLow, HighHz: b.scopeHigh, Fixed: b.scopeFixed,
+		Unsupported: b.scopeUnsupported}
 }
 
 // exec sends a set command and waits for the rig's OK (FB) / NG (FA) ack.