fix: nostr operations cause app crashing (#20)

Reviewed-on: https://git.reya.su/reya/coop-mobile/pulls/20

composeApp/src/androidMain/kotlin/su/reya/coop/ExternalSignerLauncher.kt

@@ -4,23 +4,30 @@ import android.content.Intent
 import androidx.activity.result.ActivityResult
 import androidx.activity.result.ActivityResultLauncher
 import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.withContext
 
 class ExternalSignerLauncher {
     private var launcher: ActivityResultLauncher<Intent>? = null
     private var pendingResult: CompletableDeferred<ActivityResult>? = null
+    private val mutex = Mutex()
 
     fun register(launcher: ActivityResultLauncher<Intent>) {
         this.launcher = launcher
     }
 
-    suspend fun launch(intent: Intent): ActivityResult {
-        val deferred = CompletableDeferred<ActivityResult>()
-        pendingResult = deferred
-        launcher?.launch(intent)
-            ?: throw IllegalStateException("ExternalSignerLauncher not registered")
-        return deferred.await()
+    suspend fun launch(intent: Intent): ActivityResult = mutex.withLock {
+        withContext(Dispatchers.Main) {
+            val deferred = CompletableDeferred<ActivityResult>()
+            pendingResult = deferred
+            launcher?.launch(intent) ?: throw IllegalStateException("Signer not registered")
+            deferred.await()
+        }
     }
 
+
     fun onResult(result: ActivityResult) {
         pendingResult?.complete(result)
         pendingResult = null