fix(icom): wait out the rig's session cleanup before redialling

The capture shows the spiral: a session goes deaf on CI-V (28 unanswered
commands, transport alive), the fast-fail rebuilds it, the new session answers
for one second — one state read got through — and is then strangled when the
rig purges the half-open old one. Twenty seconds a lap, no audio throughout,
and only the third or fourth session survives. When the previous session died
less than 90 s after connecting, the redial now pauses 20 s so the purge
happens BEFORE the new session, not on top of it. A long-lived session still
reconnects immediately.

internal/cat/icomnet.go

@@ -56,6 +56,15 @@ func NewIcomNet(host, user, pass string, civAddr int, digitalDefault string, aud
 		model:      "Icom",
 		scopeFixed: true,
 	}
+	// lastNetConnect is when the previous session came up, and it drives a
+	// deliberate pause: on a real IC-7760 a session sometimes goes deaf on CI-V
+	// while the rig still holds it half-open, and a session dialled straight
+	// back in answers for a second and is then strangled when the rig finally
+	// purges the old one — reconnect, die, reconnect, die, twenty seconds a
+	// lap and no audio the whole time. When the last session died YOUNG, wait
+	// out the rig's cleanup before dialling again; a session that lived long
+	// reconnects immediately, as ever.
+	var lastNetConnect time.Time
 	b.open = func() (civTransport, error) {
 		if strings.TrimSpace(host) == "" {
 			return nil, fmt.Errorf("no rig host configured")
@@ -63,7 +72,20 @@ func NewIcomNet(host, user, pass string, civAddr int, digitalDefault string, aud
 		b.dialMu.Lock()
 		cancel := b.dialCancel
 		b.dialMu.Unlock()
-		return dialIcomNet(host, user, pass, "OpsLog", b.rigAddr, cancel, audioSink)
+		if !lastNetConnect.IsZero() && time.Since(lastNetConnect) < 90*time.Second {
+			debugLog.Printf("icom net: the last session died young — pausing 20 s before redialling so the rig can purge it first")
+			for i := 0; i < 40; i++ {
+				if icnCanceled(cancel) {
+					return nil, errDialCanceled
+				}
+				time.Sleep(500 * time.Millisecond)
+			}
+		}
+		tr, err := dialIcomNet(host, user, pass, "OpsLog", b.rigAddr, cancel, audioSink)
+		if err == nil {
+			lastNetConnect = time.Now()
+		}
+		return tr, err
 	}
 	return b
 }