debug(icom): the quiet detector watches CI-V DATA, not transport chatter

The first detector counted any packet and never fired: pings and idles keep
flowing while the rig stops answering CI-V commands — which is what the 7760's
recurring silence turns out to be. Now it fires on 10 s without a CI-V payload
and reports the ages of the transport, the last scope frame and the last
socket error, so the next occurrence says exactly what the rig was still
sending.

internal/cat/icomnet.go

@@ -365,6 +365,8 @@ func (n *icomNet) civPump() {
 	// and a rig that stopped talking are different repairs, and the 30 s
 	// watchdog that follows cannot tell them apart from where it sits.
 	lastPkt := time.Now()
+	lastData := time.Now()   // CI-V payload packets (replies + transceive)
+	lastScope := time.Time{} // scope frames within those
 	var lastErr error
 	quietSaid := false
 	for {
@@ -382,7 +384,7 @@ func (n *icomNet) civPump() {
 		}
 		if err == nil && k >= 16 {
 			if quietSaid {
-				debugLog.Printf("icom net: CI-V stream is talking again after %s of silence", time.Since(lastPkt).Round(time.Second))
+				debugLog.Printf("icom net: CI-V replies are back after %s", time.Since(lastData).Round(time.Second))
 				quietSaid = false
 			}
 			lastPkt = time.Now()
@@ -398,6 +400,7 @@ func (n *icomNet) civPump() {
 				n.dead.Store(true) // make Alive() fail now → prompt clean reconnect
 				debugLog.Printf("icom net: rig sent DISCONNECT on CI-V stream — session dropped by the rig")
 			case typ == 0x00 && k > 0x15 && buf[0x10] == 0xc1: // CI-V data
+				lastData = time.Now()
 				n.trackRxSeq(icnLE.Uint16(buf[6:])) // note gaps for retransmit
 				civBytes := buf[0x15:k]
 				cp := append([]byte(nil), civBytes...)
@@ -407,6 +410,7 @@ func (n *icomNet) civPump() {
 				// feeder in IcomSerial picks them up. Everything else is a control
 				// reply → rx → Read.
 				if len(civBytes) >= 5 && civBytes[4] == 0x27 {
+					lastScope = time.Now()
 					icnEnqueueDrop(n.scopeRx, cp)
 					break
 				}
@@ -429,9 +433,14 @@ func (n *icomNet) civPump() {
 				}
 			}
 		}
-		if !quietSaid && time.Since(lastPkt) > 10*time.Second {
+		if !quietSaid && time.Since(lastData) > 10*time.Second {
 			quietSaid = true
-			debugLog.Printf("icom net: CI-V stream quiet for 10 s (control link still alive; last socket error: %v; missing-seq backlog: %d) — idles and retransmit requests are still being sent", lastErr, len(n.rxMissing))
+			scopeAge := "never"
+			if !lastScope.IsZero() {
+				scopeAge = time.Since(lastScope).Round(time.Second).String()
+			}
+			debugLog.Printf("icom net: no CI-V DATA for 10 s (transport last heard %s ago; last scope frame %s ago; last socket error: %v; missing-seq backlog: %d)",
+				time.Since(lastPkt).Round(time.Second), scopeAge, lastErr, len(n.rxMissing))
 		}
 		if time.Since(lastIdle) > 150*time.Millisecond {
 			_, _ = n.civ.Write(icnCtrl(0x00, 0, n.vID, n.vRemote))