fix: call nativeStartSignaling from Java Thread with 8MB stack, not Kotlin IO dispatcher

android/app/src/main/java/com/wzp/ui/call/CallViewModel.kt

@@ -171,9 +171,12 @@ class CallViewModel : ViewModel(), WzpCallback {
         val seed = _seedHex.value
         val alias = _alias.value
 
-        viewModelScope.launch(Dispatchers.IO) {
+        // Use a Java Thread with 8MB stack — Kotlin's IO dispatcher threads are too small
+        // for the native JNI + Rust + TLS stack requirements
         val resolvedRelay = resolveToIp(relay) ?: relay
+        Thread(null, {
             val result = engine?.startSignaling(resolvedRelay, seed, "", alias)
+            viewModelScope.launch {
                 if (result == 0) {
                     _signalState.value = 5 // Registered
                     startStatsPolling()
@@ -181,6 +184,7 @@ class CallViewModel : ViewModel(), WzpCallback {
                     _errorMessage.value = "Failed to register on relay"
                 }
             }
+        }, "wzp-register", 8 * 1024 * 1024).start()
     }
 
     /** Place a direct call to the target fingerprint */