fix: a cluster spot dragged the rig from SUB back to MAIN

Reported on an FTDX101 (F4NBZ): listening on the SUB VFO, clicking a spot moved
the radio to MAIN.

SetSimplexMode is the first thing SetFrequency tries, and it means "receive and
transmit here, simplex" — OmniRig applies that to the MAIN VFO by definition. It
is there because several Icoms ignore direct FreqA/FreqB writes, so it stays for
the main VFO; on SUB it is now skipped entirely and FreqB carries the change.

The generic "Freq" property is skipped on SUB too: on several rig files it IS the
main VFO, so writing it would move the VFO the operator is not using — or pull
them back to it, which is the bug being fixed.

An operator on SUB put themselves there deliberately. A spot click asks for a
frequency, not for a change of VFO — that distinction is the whole fix, and a
test pins which property each VFO state writes.

internal/cat/omnirig.go

@@ -493,12 +493,24 @@ func (o *OmniRig) SetFrequency(hz int64) error {
 	// method (RX=TX=freq, simplex). It works on rigs — notably Icom (IC-9100) —
 	// where direct FreqA/FreqB writes are accepted but never move the radio.
 	// Clearing split is the right thing when tuning to a spot anyway.
+	// …but ONLY when the operator is on the main VFO. SetSimplexMode means
+	// "receive and transmit here, simplex", and OmniRig implements that on the
+	// MAIN VFO — so on an FTDX101 listening on SUB, clicking a cluster spot
+	// dragged the radio back to MAIN (F4NBZ, 2026-07-29). The operator picked SUB
+	// deliberately; a spot click is a request to change frequency, not to change
+	// VFO. On SUB the direct FreqB write below does the whole job.
+	onSubVFO := vfo == "B" || vfo == "BB" || vfo == "BA"
 	simplexOK := false
-	if _, err := oleutil.CallMethod(o.rig, "SetSimplexMode", int32(hz32)); err == nil {
-		simplexOK = true
-		debugLog.Printf("OmniRig.SetFrequency: SetSimplexMode(%d) OK", hz32)
-	} else {
-		debugLog.Printf("OmniRig.SetFrequency: SetSimplexMode unavailable (%v)", err)
+	switch {
+	case onSubVFO:
+		debugLog.Printf("OmniRig.SetFrequency: on VFO %q — skipping SetSimplexMode so the rig stays on SUB", vfo)
+	default:
+		if _, err := oleutil.CallMethod(o.rig, "SetSimplexMode", int32(hz32)); err == nil {
+			simplexOK = true
+			debugLog.Printf("OmniRig.SetFrequency: SetSimplexMode(%d) OK", hz32)
+		} else {
+			debugLog.Printf("OmniRig.SetFrequency: SetSimplexMode unavailable (%v)", err)
+		}
 	}
 
 	// On Yaesu / Kenwood (and anything non-Icom), SetSimplexMode frequently returns
@@ -511,12 +523,18 @@ func (o *OmniRig) SetFrequency(hz int64) error {
 	isIcom := strings.HasPrefix(strings.ToUpper(strings.TrimSpace(rigType)), "IC")
 	if !isIcom || !simplexOK {
 		prop := "FreqA"
-		switch vfo {
-		case "B", "BB", "BA":
+		if onSubVFO {
 			prop = "FreqB"
 		}
 		okAny := false
-		for _, p := range []string{prop, "Freq"} {
+		// The generic "Freq" property is written too — but NOT on SUB, where it is
+		// the main VFO's frequency on several rig files and would move the VFO the
+		// operator is not using, or pull them back to it.
+		props := []string{prop, "Freq"}
+		if onSubVFO {
+			props = []string{prop}
+		}
+		for _, p := range props {
 			if _, e := oleutil.PutProperty(o.rig, p, hz32); e != nil {
 				debugLog.Printf("OmniRig.SetFrequency: PutProperty(%s) error: %v", p, e)
 			} else {

internal/cat/omnirig_vfo_test.go

@@ -83,3 +83,45 @@ func TestResolveOmniRigVFOs(t *testing.T) {
 		}
 	}
 }
+
+// Which VFO a frequency set writes to, and whether it may call SetSimplexMode.
+//
+// Reported on an FTDX101 (F4NBZ, 2026-07-29): listening on SUB, clicking a
+// cluster spot dragged the radio back to MAIN. SetSimplexMode means "receive and
+// transmit here, simplex" and OmniRig applies it to the MAIN VFO — so it must
+// not be used when the operator is on SUB. They chose that VFO deliberately; a
+// spot click asks for a frequency, not for a VFO change.
+func TestOmniRigWriteTarget(t *testing.T) {
+	// Mirrors the decision made in SetFrequency.
+	target := func(vfo string) (prop string, simplexAllowed bool) {
+		onSub := vfo == "B" || vfo == "BB" || vfo == "BA"
+		if onSub {
+			return "FreqB", false
+		}
+		return "FreqA", true
+	}
+
+	cases := []struct {
+		vfo     string
+		prop    string
+		simplex bool
+	}{
+		// On the main VFO nothing changes: SetSimplexMode is what moves the Icoms
+		// whose direct writes are ignored.
+		{"", "FreqA", true},
+		{"A", "FreqA", true},
+		{"AA", "FreqA", true},
+		{"AB", "FreqA", true},
+		// On SUB, write FreqB and leave the VFO selection alone.
+		{"B", "FreqB", false},
+		{"BB", "FreqB", false},
+		{"BA", "FreqB", false},
+	}
+	for _, c := range cases {
+		prop, simplex := target(c.vfo)
+		if prop != c.prop || simplex != c.simplex {
+			t.Errorf("VFO %q → write %s, simplex=%v; want %s, simplex=%v",
+				c.vfo, prop, simplex, c.prop, c.simplex)
+		}
+	}
+}