up

app.go

@@ -359,6 +359,7 @@ type App struct {
 	dvkRecSlot int  // slot currently being recorded (DVKStartRecord → DVKStopRecord)
 	dvkPttKeyed bool // we keyed PTT for a voice message; unkey when it ends
 	pttMu         sync.Mutex
+	udpLogMu      sync.Mutex // serialises UDP auto-log so concurrent packets can't both pass the dedup check
 	pttPort       serial.Port // open serial port while PTT (RTS/DTR) is asserted
 	pttKeyedMethod string     // "cat" | "rts" | "dtr" while keyed; "" when idle
 	pttGen        int64       // bumped on every key; a delayed unkey only fires if unchanged (guards against a stale release cutting a new transmission)
@@ -5273,11 +5274,18 @@ func (a *App) LogUDPLoggedADIF(adifText string) (int64, error) {
 	a.refineDistrictZones(&q)          // W6 → CQ3/ITU6 for zone-split countries
 	a.applyQSLDefaults(&q)
 
-	// ── Dedup ──
+	// ── Dedup (serialised) ──
 	// Match by call + band + mode within a ±2-minute window: a QSO logged
 	// manually in OpsLog and re-broadcast by Log4OM over UDP often differs by
 	// a minute (the two apps stamp their own time), so a minute-exact key
 	// missed it and the contact got duplicated.
+	//
+	// The check + insert is guarded by udpLogMu: MSHV/WSJT can deliver the same
+	// logged-QSO packet twice in quick succession (re-broadcast, or two
+	// listeners), and without serialisation both goroutines read the dedup set
+	// BEFORE either inserts, both pass, and the QSO lands twice.
+	a.udpLogMu.Lock()
+	defer a.udpLogMu.Unlock()
 	seen, err := a.qso.ExistingDedupeKeys(a.ctx)
 	if err == nil {
 		base := q.QSODate.UTC()