fix(icom): the client pings too — the dropouts' likely root cause

wfview sends a ping (0x07, 0x15 bytes, its own seq and a monotonic
timestamp) every 500 ms on every stream, and so does RS-BA1. OpsLog only
ever REPLIED to the rig's pings — and the loaner IC-7760 stopped serving
CI-V data about a minute into nearly every session while the transport
stayed alive: the rig had concluded nobody was listening. Scope, TX audio
and idle numbering were each eliminated in turn before wfview's source
settled it. Pings now go out on control, CI-V and audio alike.

internal/cat/icomaudio.go

@@ -57,7 +57,9 @@ type icomAudio struct {
 	rxLastSeq uint16
 	rxMissing map[uint16]int
 
-	dumped int // packets hex-dumped so far (≤ icaDumpFirst)
+	dumped  int    // packets hex-dumped so far (≤ icaDumpFirst)
+	pingSeq uint16 // client-ping counter — the rig wants OUR pings too (see icnPing)
+	started time.Time
 
 	// Live-TX state — see SendTXChunk.
 	txMu    sync.Mutex
@@ -109,6 +111,7 @@ func dialIcomAudio(host string, sink func([]byte), cancel <-chan struct{}) (*ico
 	_ = conn.SetReadBuffer(1 << 20)
 	a := &icomAudio{
 		conn: conn, aID: aID, aRemote: aRemote,
+		started:   time.Now(),
 		sink:      sink,
 		rxMissing: make(map[uint16]int),
 		done:      make(chan struct{}),
@@ -124,6 +127,7 @@ func dialIcomAudio(host string, sink func([]byte), cancel <-chan struct{}) (*ico
 func (a *icomAudio) audioPump() {
 	buf := make([]byte, 8192)
 	lastIdle := time.Now()
+	lastPing := time.Now()
 	lastReq := time.Now()
 	for {
 		select {
@@ -163,6 +167,11 @@ func (a *icomAudio) audioPump() {
 			_, _ = a.conn.Write(icnCtrl(0x00, 0, a.aID, a.aRemote))
 			lastIdle = time.Now()
 		}
+		if time.Since(lastPing) > 500*time.Millisecond {
+			a.pingSeq++
+			_, _ = a.conn.Write(icnPing(a.pingSeq, a.aID, a.aRemote, uint32(time.Since(a.started).Milliseconds())))
+			lastPing = time.Now()
+		}
 		if time.Since(lastReq) > 100*time.Millisecond {
 			a.sendRetransmitReq()
 			lastReq = time.Now()