fix(icom): CI-V idles carry real sequence numbers

Every idle went out with seq 0, seven a second, interleaved with
properly-numbered data — where RS-BA1 and wfview draw idle sequence numbers
from the same counter as everything else. A rig that follows the sequence
tolerates the zeros for a minute or so and then stops serving CI-V data on
the stream: the shape of every dropout the loaner IC-7760 has shown, with the
scope and the TX path both since eliminated as causes. Idles now take the
next tracked seq and sit in the retransmit buffer like any other packet.

internal/cat/icomnet.go

@@ -510,7 +510,23 @@ func (n *icomNet) civPump() {
 			debugLog.Printf("icom net: the reopen did not bring CI-V back — forcing a fresh session")
 		}
 		if time.Since(lastIdle) > 150*time.Millisecond {
-			_, _ = n.civ.Write(icnCtrl(0x00, 0, n.vID, n.vRemote))
+			// Idles carry a REAL sequence number, drawn from the same counter as
+			// the data packets, and sit in the retransmit buffer like them —
+			// which is how RS-BA1 and wfview number theirs. Ours used seq 0 on
+			// every idle, seven a second, interleaved with properly-numbered
+			// data; a rig that follows the sequence tolerates that for a minute
+			// or so and then stops serving CI-V data on the stream — which is
+			// the shape of every dropout this loaner IC-7760 has shown, with
+			// the scope and the TX path both since eliminated.
+			n.seqMu.Lock()
+			iseq := n.vTracked
+			n.vTracked++
+			n.seqMu.Unlock()
+			ipkt := icnCtrl(0x00, iseq, n.vID, n.vRemote)
+			n.sentMu.Lock()
+			n.sentBuf[iseq] = ipkt
+			n.sentMu.Unlock()
+			_, _ = n.civ.Write(ipkt)
 			lastIdle = time.Now()
 		}
 		if time.Since(lastReq) > 100*time.Millisecond {