fix(ios): fix thread-safety race in skipDescriptorDiscovery on reconnect (#809)

On reconnect, CoreBluetooth uses cached GATT data and fires
didDiscoverCharacteristicsFor near-instantly on the main queue, before
the bridge thread's write to skipDescriptorDiscovery is visible — causing
the stale false value to be read and the connection to time out.

Fix by dispatching setOnConnected synchronously to the main queue, matching
the queue CoreBluetooth delegates run on. Apply the same fix to
startScanning's scan filter properties for the same reason. Add comments
on stateReceiver where the same issue exists but is too slow to manifest.

Author: peitschie

ios/Sources/BluetoothLe/Device.swift

@@ -52,10 +52,14 @@ class Device: NSObject, CBPeripheralDelegate {
         _ skipDescriptorDiscovery: Bool,
         _ callback: @escaping Callback
     ) {
-        let key = "connect"
-        self.skipDescriptorDiscovery = skipDescriptorDiscovery
-        self.callbackMap[key] = callback
-        self.setTimeout(key, "Connection timeout", connectionTimeout)
+        // Delegates run on the main queue; this is called from the bridge thread.
+        // Sync to main so writes are visible before any delegate fires.
+        DispatchQueue.main.sync {
+            let key = "connect"
+            self.skipDescriptorDiscovery = skipDescriptorDiscovery
+            self.callbackMap[key] = callback
+            self.setTimeout(key, "Connection timeout", connectionTimeout)
+        }
     }
 
     func peripheral(

ios/Sources/BluetoothLe/DeviceManager.swift

@@ -73,6 +73,9 @@ class DeviceManager: NSObject, CBCentralManagerDelegate {
         return self.centralManager.state == CBManagerState.poweredOn
     }
 
+    // stateReceiver is written on the bridge thread and read on the main queue
+    // (via centralManagerDidUpdateState). Same threading issue as startScanning
+    // below; not fixed as BLE state transitions are too slow for the race to manifest.
     func registerStateReceiver( _ stateReceiver: @escaping StateReceiver) {
         self.stateReceiver = stateReceiver
     }
@@ -99,16 +102,21 @@ class DeviceManager: NSObject, CBCentralManagerDelegate {
         _ scanResultCallback: @escaping ScanResultCallback
     ) {
         self.callbackMap["startScanning"] = callback
-        self.scanResultCallback = scanResultCallback
 
         if self.centralManager.isScanning == false {
             self.discoveredDevices.removeAll()
-            self.deviceListMode = deviceListMode
-            self.allowDuplicates = allowDuplicates
-            self.deviceNameFilter = name
-            self.deviceNamePrefixFilter = namePrefix
-            self.manufacturerDataFilters = manufacturerDataFilters
-            self.serviceDataFilters = serviceDataFilters
+            // These are read from centralManager(_:didDiscover:) on the main queue.
+            // Delegates run on the main queue; this is called from the bridge thread.
+            // Sync to main so writes are visible before any delegate fires.
+            DispatchQueue.main.sync {
+                self.scanResultCallback = scanResultCallback
+                self.deviceListMode = deviceListMode
+                self.allowDuplicates = allowDuplicates
+                self.deviceNameFilter = name
+                self.deviceNamePrefixFilter = namePrefix
+                self.manufacturerDataFilters = manufacturerDataFilters
+                self.serviceDataFilters = serviceDataFilters
+            }
 
             if deviceListMode != .none {
                 self.showDeviceList()