fix(icom): one sequence space for everything sent on the audio stream

The voice keyer and the live microphone each numbered their packets from 1.
A message played after a talk session re-used sequence numbers the rig had
already seen and was discarded wholesale: the PTT keyed for the full length
of the message and none of it was modulated. PlayTX now feeds the same framer
and counters as the microphone.

internal/cat/icomaudio.go

@@ -260,11 +260,14 @@ func (a *icomAudio) PlayTX(pcm []byte, rate, ch, bits int, stop <-chan struct{})
 	if rate > 0 && rate != 16000 {
 		mono = resampleLinear(mono, rate, 16000)
 	}
+	// Through the SAME framer and counters as the live microphone. Each of the
+	// two used to number its own packets from 1, and a voice-keyer message sent
+	// after a talk session re-used sequence numbers the rig had already seen —
+	// it keyed for the full length of the message and modulated none of it.
 	const frame = 320 // samples per packet: 20 ms at 16 kHz, the rig's own cadence
 	tick := time.NewTicker(20 * time.Millisecond)
 	defer tick.Stop()
-	var outerSeq uint16 = 1
-	var sendSeq uint16
+	buf := make([]byte, frame*2)
 	for pos := 0; pos < len(mono); pos += frame {
 		select {
 		case <-stop:
@@ -273,28 +276,21 @@ func (a *icomAudio) PlayTX(pcm []byte, rate, ch, bits int, stop <-chan struct{})
 			return fmt.Errorf("the audio stream closed mid-message")
 		case <-tick.C:
 		}
-		pkt := make([]byte, 0x18+frame*2)
-		icnLE.PutUint32(pkt[0:], uint32(len(pkt)))
-		icnLE.PutUint16(pkt[6:], outerSeq)
-		icnLE.PutUint32(pkt[8:], a.aID)
-		icnLE.PutUint32(pkt[12:], a.aRemote)
-		pkt[0x10], pkt[0x11] = 0x81, 0x01
-		icnBE.PutUint16(pkt[0x12:], sendSeq)
-		icnBE.PutUint32(pkt[0x14:], frame*2)
-		for i := 0; i < frame && pos+i < len(mono); i++ {
-			v := mono[pos+i] * 32767
+		for i := 0; i < frame; i++ {
+			var v float32
+			if pos+i < len(mono) {
+				v = mono[pos+i] * 32767
+			}
 			if v > 32767 {
 				v = 32767
 			} else if v < -32768 {
 				v = -32768
 			}
-			icnLE.PutUint16(pkt[0x18+i*2:], uint16(int16(v)))
+			icnLE.PutUint16(buf[i*2:], uint16(int16(v)))
 		}
-		if _, err := a.conn.Write(pkt); err != nil {
-			return fmt.Errorf("sending audio to the rig: %w", err)
+		if err := a.SendTXChunk(buf); err != nil {
+			return err
 		}
-		outerSeq++
-		sendSeq++
 	}
 	return nil
 }