fix: check writeCharacteristic return value in sendOtaData

android/app/src/main/java/nl/eddydevink/sylda/BleRelayManager.kt

@@ -194,12 +194,12 @@ class BleRelayManager(
     }
 
     @SuppressLint("MissingPermission")
-    fun sendOtaData(data: ByteArray) {
-        val char = otaCharacteristic ?: return
-        val gatt = bluetoothGatt ?: return
+    fun sendOtaData(data: ByteArray): Boolean {
+        val char = otaCharacteristic ?: return false
+        val gatt = bluetoothGatt ?: return false
         char.value = data
         char.writeType = BluetoothGattCharacteristic.WRITE_TYPE_NO_RESPONSE
-        gatt.writeCharacteristic(char)
+        return gatt.writeCharacteristic(char)
     }
 
     @SuppressLint("MissingPermission")

android/app/src/main/java/nl/eddydevink/sylda/OtaManager.kt

@@ -105,7 +105,13 @@ class OtaManager(
                 var retries = 0
 
                 while (retries < MAX_RETRIES) {
-                    relayManager.sendOtaData(packet.array())
+                    val writeOk = relayManager.sendOtaData(packet.array())
+                    if (!writeOk) {
+                        Log.w(TAG, "writeCharacteristic returned false for chunk $seq, retrying")
+                        retries++
+                        delay(100)
+                        continue
+                    }
                     Log.d(TAG, "Sent chunk $seq/$totalChunks ($chunkSize bytes) attempt ${retries + 1}")
 
                     try {