diag(icom net): name the last CI-V commands before the silence

Audio off, and the IC-7760 still answers at connect and then never again:
twenty-eight commands sent, not one reply, packets still arriving on the
stream. A count says how much went unanswered and never which command
went out last — which is the one thing that can identify a frame this rig
does not tolerate, on a radio nobody here has.

The transport now keeps the command headers of the last eight frames and
prints them with the silence report.

internal/cat/icomnet.go

@@ -132,6 +132,13 @@ type icomNet struct {
 	// loop, not the rig — and RS-BA1 showing no such dropouts points that way.
 	txCiv    atomic.Uint32
 	txAtData atomic.Uint32
+	// WHAT was asked, not just how much. A rig that answers at connect and then
+	// never again has usually been sent something it does not like, and counting
+	// the unanswered commands says nothing about which one that was. The last few
+	// command headers are kept so the silence report can name them — the only way
+	// to find a poison command on a radio nobody here has.
+	cmdMu   sync.Mutex
+	lastCmd []string
 
 	rx      chan []byte // CI-V byte chunks from civPump → Read (control replies)
 	scopeRx chan []byte // scope (0x27) frames, kept off rx so the panadapter
@@ -268,6 +275,7 @@ func (n *icomNet) Write(p []byte) (int, error) {
 	n.vCivSeq++
 	n.seqMu.Unlock()
 	n.txCiv.Add(1)
+	n.noteCmd(p)
 	pkt := icnCivData(seq, n.vID, n.vRemote, civSeq, p)
 	n.sentMu.Lock()
 	n.sentBuf[seq] = pkt
@@ -280,6 +288,35 @@ func (n *icomNet) Write(p []byte) (int, error) {
 	return len(p), nil
 }
 
+// noteCmd remembers the command bytes of a CI-V frame — everything after the
+// preamble and the two addresses, up to four bytes, which is command,
+// sub-command and the first of the data.
+func (n *icomNet) noteCmd(p []byte) {
+	if len(p) < 5 {
+		return
+	}
+	body := p[4:]
+	if len(body) > 4 {
+		body = body[:4]
+	}
+	n.cmdMu.Lock()
+	n.lastCmd = append(n.lastCmd, fmt.Sprintf("% X", body))
+	if len(n.lastCmd) > 8 {
+		n.lastCmd = n.lastCmd[len(n.lastCmd)-8:]
+	}
+	n.cmdMu.Unlock()
+}
+
+// recentCmds is what noteCmd collected, oldest first.
+func (n *icomNet) recentCmds() string {
+	n.cmdMu.Lock()
+	defer n.cmdMu.Unlock()
+	if len(n.lastCmd) == 0 {
+		return "none"
+	}
+	return strings.Join(n.lastCmd, " | ")
+}
+
 // icnTrace toggles verbose per-frame CI-V request/reply logging for diagnosing
 // the network transport. Off by default (the connect-step logs stay); flip to
 // true to trace every TX/RX again.
@@ -496,6 +533,7 @@ func (n *icomNet) civPump() {
 			}
 			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; CI-V commands SENT since the last answer: %d)",
 				time.Since(lastPkt).Round(time.Second), scopeAge, lastErr, len(n.rxMissing), n.txCiv.Load()-n.txAtData.Load())
+			debugLog.Printf("icom net: the last CI-V commands sent, oldest first: %s", n.recentCmds())
 			// THE AUDIO STREAM IS THE FIRST SUSPECT, AND ONLY THE LOG CAN SAY SO.
 			//
 			// The RX audio stream is experimental and shares the rig's session with