feat(sat): Doppler tracking on the radio

The hard part of satellite tuning is not the arithmetic, it is deciding
who owns the dial. A tracker that forces both frequencies fights the
operator every time they turn the knob to follow a station across a
linear transponder; one that never touches the receiver leaves them
chasing a signal that slides nine kilohertz across a 70 cm pass.

So the operator owns the receiver and the tracker follows them. Every
second it asks the radio where the receiver actually is. Where it put it,
nothing has changed. Further than a dial-turn's tolerance, and the
operator has chosen a station: what they landed on is converted back into
a nominal frequency, and the transmitter is derived from that. Which is
the division of labour on a linear bird — the operator listens, the radio
does the sums.

Three ways to reach the radio, because a satellite pair is a shape of
operating rather than a manufacturer's feature. An IC-9700 or IC-9100 is
asked for its OWN satellite mode: it pairs main and sub, gives full
duplex, and keeps the dials linked the way its designers meant, which is
always better than an imitation built out of split. A Flex gets two
slices, A the downlink and B the uplink, created when missing, because
"slice B does not exist" is not something to make an operator fix at the
start of a ten-minute pass. Everything else gets the downlink, and is
told so — half the job announced beats half the job hidden.

What goes in the log is the NOMINAL pair. Two stations working each other
through a transponder read different numbers off their dials at the same
instant; the only figure they can both agree on is the transponder's own.
FREQ is the uplink and FREQ_RX the downlink — the one place a satellite
QSO differs from every other kind, and the reason FREQ alone cannot
describe one.

internal/cat/flex.go

@@ -67,6 +67,14 @@ type Flex struct {
 	pendingSpot     map[int]string // seq → callsign, awaiting the spot index in the R response
 	pendingSpotMode map[int]string // seq → ADIF mode, paired with pendingSpot
 	pendingSplit    map[int]bool   // seq → awaiting the new TX slice's index (split create)
+	pendingSat      map[int]string // seq → "rx"/"tx", awaiting a satellite slice's index
+	// Satellite pair: slice A is the downlink, slice B the uplink. -1 when not
+	// armed. satCreatedTX marks an uplink slice OpsLog opened, and is the only
+	// one it will close again.
+	satOn        bool
+	satRX        int
+	satTX        int
+	satCreatedTX bool
 	spotCall        map[int]string // spot index → callsign (to fill the call on a panadapter click)
 	spotMode        map[int]string // spot index → ADIF mode, so a click can also set the slice mode (SmartSDR tunes the spot's freq but not its mode)
 	spotFreq        map[int]int64  // spot index → Hz, so a click can report where it was (the trigger message carries only the index)
@@ -227,7 +235,7 @@ func NewFlex(host string, port int, spotsEnabled bool) *Flex {
 	return &Flex{
 		host: strings.TrimSpace(host), port: port,
 		slices: map[int]*flexSlice{}, spotsEnabled: spotsEnabled,
-		spotIdx: map[int]bool{}, pendingSpot: map[int]string{}, pendingSpotMode: map[int]string{}, spotCall: map[int]string{}, spotMode: map[int]string{}, spotFreq: map[int]int64{}, pendingSpotFreq: map[int]int64{}, panWindow: map[string]panView{}, spotSig: map[string]string{}, spotSent: map[string]time.Time{}, spotByCall: map[string]int{}, pendingSplit: map[int]bool{},
+		spotIdx: map[int]bool{}, pendingSpot: map[int]string{}, pendingSpotMode: map[int]string{}, spotCall: map[int]string{}, spotMode: map[int]string{}, spotFreq: map[int]int64{}, pendingSpotFreq: map[int]int64{}, panWindow: map[string]panView{}, spotSig: map[string]string{}, spotSent: map[string]time.Time{}, spotByCall: map[string]int{}, pendingSplit: map[int]bool{}, pendingSat: map[int]string{}, satRX: -1, satTX: -1,
 		meterMeta: map[int]meterInfo{}, meterVal: map[int]float64{}, meterSub: map[int]bool{},
 		sentCmds: map[int]string{}, txSetAt: map[string]time.Time{},
 		pinnedSlice: -1,
@@ -458,12 +466,23 @@ func (f *Flex) reader(conn net.Conn) {
 			if splitSeq {
 				delete(f.pendingSplit, seq)
 			}
+			// The same reply carries the index of a slice created for a satellite
+			// pair; which of the two it is was recorded when it was asked for.
+			satRole := f.pendingSat[seq]
+			if satRole != "" {
+				delete(f.pendingSat, seq)
+			}
 			f.mu.Unlock()
 			if splitSeq && ok && len(parts) >= 3 {
 				if idx, e := strconv.Atoi(strings.TrimSpace(parts[2])); e == nil {
 					f.send(fmt.Sprintf("slice s %d tx=1", idx))
 				}
 			}
+			if satRole != "" && ok && len(parts) >= 3 {
+				if idx, e := strconv.Atoi(strings.TrimSpace(parts[2])); e == nil {
+					f.adoptSatSlice(satRole, idx)
+				}
+			}
 		}
 	}
 	// Connection ended.