fix: Bug showing split for flex while in different mode on same band

internal/cat/flex.go

@@ -919,9 +919,11 @@ func (f *Flex) txSliceLocked() *flexSlice {
 // operatingLocked resolves the operator's slices: the MAIN (active) slice for the
 // mode/display, and — ONLY for a GENUINE split — the RX and TX slices. Split is
 // the tx-flagged slice PLUS a distinct in-use slice on the SAME band (different
-// freq) — detected from the pair itself, NOT from which slice is active (the TX
-// slice often steals focus right after "slice create", which must NOT read as
-// "no split"). A slice on another band is an independent receiver, ignored.
+// freq) AND the SAME split class (both PHONE, or both CW) — detected from the
+// pair itself, NOT from which slice is active (the TX slice often steals focus
+// right after "slice create", which must NOT read as "no split"). A slice on
+// another band is an independent receiver, ignored; so is a same-band slice in a
+// different mode (SSB + FT8) or a data mode (FT8/FT4/RTTY never split).
 // Caller holds f.mu.
 func (f *Flex) operatingLocked() (main, rx, tx *flexSlice) {
 	_, main = f.mainSliceLocked()
@@ -933,21 +935,31 @@ func (f *Flex) operatingLocked() (main, rx, tx *flexSlice) {
 	if bt == "" {
 		return main, nil, nil
 	}
-	// RX = the active slice when it's a distinct same-band slice, else the first
-	// other in-use same-band slice.
-	if main != nil && main != txS && main.freqHz != txS.freqHz && BandFromHz(main.freqHz) == bt {
+	// Split only applies to PHONE/CW; a data-mode TX slice never splits.
+	ct := flexSplitClass(txS.mode)
+	if ct == "" {
+		return main, nil, nil
+	}
+	// A split partner is an in-use, same-band slice at a different freq in the
+	// SAME split class (so SSB + FT8 on one band is NOT a split).
+	sameSplit := func(s *flexSlice) bool {
+		return s != nil && s.inUse && s != txS && s.freqHz != txS.freqHz &&
+			BandFromHz(s.freqHz) == bt && flexSplitClass(s.mode) == ct
+	}
+	// RX = the active slice when it qualifies, else the first other qualifying
+	// same-band slice.
+	if sameSplit(main) {
 		rx = main
 	} else {
 		for _, idx := range f.sortedSliceIdxLocked() {
-			s := f.slices[idx]
-			if s.inUse && s != txS && s.freqHz != txS.freqHz && BandFromHz(s.freqHz) == bt {
+			if s := f.slices[idx]; sameSplit(s) {
 				rx = s
 				break
 			}
 		}
 	}
 	if rx == nil {
-		return main, nil, nil // tx slice alone (simplex) → not split
+		return main, nil, nil // tx slice alone (simplex) or no same-mode partner → not split
 	}
 	return main, rx, txS
 }
@@ -1921,6 +1933,23 @@ func parseFloatDefault(s string, def float64) float64 {
 }
 
 // flexModeToADIF maps a Flex slice mode to a generic ADIF mode.
+// flexSplitClass groups a raw Flex slice mode into a split-capable class. A
+// genuine split (one RX freq, one TX freq, SAME mode) only makes sense for PHONE
+// and CW pileups. Data modes (FT8/FT4/RTTY all report as DIGU/DIGL/RTTY on a
+// Flex) and digital voice never operate split, so they return "" (not
+// split-capable). Two same-band slices whose classes differ (e.g. SSB + FT8) are
+// independent operations, not a split.
+func flexSplitClass(rawMode string) string {
+	switch flexModeToADIF(rawMode) {
+	case "SSB", "AM", "FM":
+		return "PHONE"
+	case "CW":
+		return "CW"
+	default: // DATA, RTTY, DIGITALVOICE, "" → never split
+		return ""
+	}
+}
+
 func flexModeToADIF(m string) string {
 	switch strings.ToUpper(strings.TrimSpace(m)) {
 	case "USB", "LSB":