refactor: separate SignalManager from WzpEngine for direct calling

SignalManager (NEW):
- Dedicated Rust struct with its own QUIC connection to _signal
- Separate JNI handle (nativeSignalConnect/GetState/PlaceCall/etc)
- Kotlin wrapper polls state every 500ms via getState() JSON
- Lives independently of WzpEngine — survives across calls
- connect() blocks briefly on 8MB thread, then recv loop runs on dedicated thread

WzpEngine (CLEANED):
- Back to pure media-only role (audio, codec, FEC, jitter)
- Removed start_signaling/place_call/answer_call methods
- Removed signal_transport/signal_fingerprint from EngineState

CallViewModel:
- Two separate managers: signalManager (persistent) + engine (per-call)
- Two separate polling loops: signalPollJob + statsJob
- Auto-connect to media room when signal polling detects "setup" state
- hangupDirectCall() ends media but keeps signal alive

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

android/app/src/main/java/com/wzp/engine/SignalManager.kt

@@ -0,0 +1,97 @@
+package com.wzp.engine
+
+import org.json.JSONObject
+
+/**
+ * Persistent signal connection for direct 1:1 calls.
+ * Separate from WzpEngine — survives across calls.
+ *
+ * Lifecycle: connect() → [placeCall/answerCall] → destroy()
+ */
+class SignalManager {
+
+    private var handle: Long = 0L
+
+    val isConnected: Boolean get() = handle != 0L
+
+    /**
+     * Connect to relay and register for direct calls.
+     * MUST be called from a thread with sufficient stack (8MB).
+     * Blocks briefly during QUIC connect + register, then returns.
+     */
+    fun connect(relay: String, seedHex: String): Boolean {
+        if (handle != 0L) return true // already connected
+        handle = nativeSignalConnect(relay, seedHex)
+        return handle != 0L
+    }
+
+    /** Get current signal state as parsed object. Non-blocking. */
+    fun getState(): SignalState {
+        if (handle == 0L) return SignalState()
+        val json = nativeSignalGetState(handle) ?: return SignalState()
+        return try {
+            val obj = JSONObject(json)
+            SignalState(
+                status = obj.optString("status", "idle"),
+                fingerprint = obj.optString("fingerprint", ""),
+                incomingCallId = if (obj.isNull("incoming_call_id")) null else obj.optString("incoming_call_id"),
+                incomingCallerFp = if (obj.isNull("incoming_caller_fp")) null else obj.optString("incoming_caller_fp"),
+                incomingCallerAlias = if (obj.isNull("incoming_caller_alias")) null else obj.optString("incoming_caller_alias"),
+                callSetupRelay = if (obj.isNull("call_setup_relay")) null else obj.optString("call_setup_relay"),
+                callSetupRoom = if (obj.isNull("call_setup_room")) null else obj.optString("call_setup_room"),
+                callSetupId = if (obj.isNull("call_setup_id")) null else obj.optString("call_setup_id"),
+            )
+        } catch (e: Exception) {
+            SignalState()
+        }
+    }
+
+    /** Place a direct call to a target fingerprint. */
+    fun placeCall(targetFp: String): Int {
+        if (handle == 0L) return -1
+        return nativeSignalPlaceCall(handle, targetFp)
+    }
+
+    /** Answer an incoming call. mode: 0=Reject, 1=AcceptTrusted, 2=AcceptGeneric */
+    fun answerCall(callId: String, mode: Int = 2): Int {
+        if (handle == 0L) return -1
+        return nativeSignalAnswerCall(handle, callId, mode)
+    }
+
+    /** Send hangup signal. */
+    fun hangup() {
+        if (handle != 0L) nativeSignalHangup(handle)
+    }
+
+    /** Destroy the signal manager. */
+    fun destroy() {
+        if (handle != 0L) {
+            nativeSignalDestroy(handle)
+            handle = 0L
+        }
+    }
+
+    // JNI native methods
+    private external fun nativeSignalConnect(relay: String, seed: String): Long
+    private external fun nativeSignalGetState(handle: Long): String?
+    private external fun nativeSignalPlaceCall(handle: Long, targetFp: String): Int
+    private external fun nativeSignalAnswerCall(handle: Long, callId: String, mode: Int): Int
+    private external fun nativeSignalHangup(handle: Long)
+    private external fun nativeSignalDestroy(handle: Long)
+
+    companion object {
+        init { System.loadLibrary("wzp_android") }
+    }
+}
+
+/** Signal connection state. */
+data class SignalState(
+    val status: String = "idle",
+    val fingerprint: String = "",
+    val incomingCallId: String? = null,
+    val incomingCallerFp: String? = null,
+    val incomingCallerAlias: String? = null,
+    val callSetupRelay: String? = null,
+    val callSetupRoom: String? = null,
+    val callSetupId: String? = null,
+)

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

@@ -141,9 +141,9 @@ class CallViewModel : ViewModel(), WzpCallback {
     private val _targetFingerprint = MutableStateFlow("")
     val targetFingerprint: StateFlow<String> = _targetFingerprint.asStateFlow()
 
-    /** Signal connection state: 0=idle, 5=registered, 6=ringing, 7=incoming */
-    private val _signalState = MutableStateFlow(0)
-    val signalState: StateFlow<Int> = _signalState.asStateFlow()
+    /** Signal state string: "idle", "registered", "ringing", "incoming", "setup" */
+    private val _signalState = MutableStateFlow("idle")
+    val signalState: StateFlow<String> = _signalState.asStateFlow()
 
     /** Incoming call info */
     private val _incomingCallId = MutableStateFlow<String?>(null)
@@ -155,37 +155,65 @@ class CallViewModel : ViewModel(), WzpCallback {
     private val _incomingCallerAlias = MutableStateFlow<String?>(null)
     val incomingCallerAlias: StateFlow<String?> = _incomingCallerAlias.asStateFlow()
 
+    /** Separate signal manager (persistent, survives calls) */
+    private var signalManager: com.wzp.engine.SignalManager? = null
+    private var signalPollJob: Job? = null
+
     fun setCallMode(mode: Int) { _callMode.value = mode }
     fun setTargetFingerprint(fp: String) { _targetFingerprint.value = fp }
 
     /** Register on relay for direct calls */
     fun registerForCalls() {
-        if (engine == null) {
-            engine = WzpEngine(this).also { it.init() }
-        }
         val serverIdx = _selectedServer.value
         val serverList = _servers.value
         if (serverIdx >= serverList.size) return
 
         val relay = serverList[serverIdx].address
         val seed = _seedHex.value
-        val alias = _alias.value
-
-        // Start stats polling BEFORE blocking — startSignaling blocks the thread forever
-        startStatsPolling()
-
-        // Use a Java Thread with 8MB stack — blocks forever in signal recv loop
         val resolvedRelay = resolveToIp(relay) ?: relay
+
+        // Connect on a thread with 8MB stack (QUIC + TLS needs it)
         Thread(null, {
-            val result = engine?.startSignaling(resolvedRelay, seed, "", alias)
-            // Only reached if signaling disconnects
+            val mgr = com.wzp.engine.SignalManager()
+            val ok = mgr.connect(resolvedRelay, seed)
             viewModelScope.launch {
-                if (result != 0) {
-                    _errorMessage.value = "Signal connection lost"
+                if (ok) {
+                    signalManager = mgr
+                    startSignalPolling()
+                } else {
+                    _errorMessage.value = "Failed to register on relay"
                 }
-                _signalState.value = 0
             }
-        }, "wzp-register", 8 * 1024 * 1024).start()
+        }, "wzp-signal-connect", 8 * 1024 * 1024).start()
+    }
+
+    /** Poll signal manager state every 500ms */
+    private fun startSignalPolling() {
+        signalPollJob?.cancel()
+        signalPollJob = viewModelScope.launch {
+            while (isActive) {
+                val mgr = signalManager
+                if (mgr != null && mgr.isConnected) {
+                    val state = mgr.getState()
+                    _signalState.value = state.status
+                    _incomingCallId.value = state.incomingCallId
+                    _incomingCallerFp.value = state.incomingCallerFp
+                    _incomingCallerAlias.value = state.incomingCallerAlias
+
+                    // Auto-connect to media room when call is set up
+                    if (state.status == "setup" && state.callSetupRelay != null && state.callSetupRoom != null) {
+                        Log.i(TAG, "CallSetup: connecting to ${state.callSetupRelay} room ${state.callSetupRoom}")
+                        startCallInternal(state.callSetupRelay, state.callSetupRoom)
+                    }
+                }
+                delay(500L)
+            }
+        }
+    }
+
+    private fun stopSignalPolling() {
+        signalPollJob?.cancel()
+        signalPollJob = null
     }
 
     /** Place a direct call to the target fingerprint */
@@ -195,24 +223,28 @@ class CallViewModel : ViewModel(), WzpCallback {
             _errorMessage.value = "Enter a fingerprint to call"
             return
         }
-        engine?.placeCall(target)
-        _signalState.value = 6 // Ringing
+        signalManager?.placeCall(target)
     }
 
     /** Answer an incoming direct call */
     fun answerIncomingCall(mode: Int = 2) {
         val callId = _incomingCallId.value ?: return
-        engine?.answerCall(callId, mode)
+        signalManager?.answerCall(callId, mode)
     }
 
     /** Reject an incoming direct call */
     fun rejectIncomingCall() {
         val callId = _incomingCallId.value ?: return
-        engine?.answerCall(callId, 0) // 0 = Reject
-        _signalState.value = 5 // Back to registered
-        _incomingCallId.value = null
-        _incomingCallerFp.value = null
-        _incomingCallerAlias.value = null
+        signalManager?.answerCall(callId, 0)
+    }
+
+    /** Hang up direct call — media ends, signal stays alive */
+    fun hangupDirectCall() {
+        signalManager?.hangup()
+        engine?.stopCall()
+        engine?.destroy()
+        engine = null
+        engineInitialized = false
     }
 
     companion object {
@@ -690,30 +722,10 @@ class CallViewModel : ViewModel(), WzpCallback {
                         val s = CallStats.fromJson(json)
                         lastCallDuration = s.durationSecs
                         _stats.value = s
-                        // Track signal state changes for direct calling
-                        if (s.state in 5..7) {
-                            _signalState.value = s.state
-                            // Don't update callState for signal-only states
-                        } else if (s.state != 0) {
+                        // Only update callState from media engine stats (not signal)
+                        if (s.state != 0) {
                             _callState.value = s.state
                         }
-                        // Incoming call detection
-                        if (s.state == 7) { // IncomingCall
-                            _incomingCallId.value = s.incomingCallId
-                            _incomingCallerFp.value = s.incomingCallerFp
-                            _incomingCallerAlias.value = s.incomingCallerAlias
-                        }
-                        // CallSetup: auto-connect to media room
-                        if (s.state == 1 && s.incomingCallId != null && s.incomingCallId.contains("|")) {
-                            // Format: "relay_addr|room_name"
-                            val parts = s.incomingCallId.split("|", limit = 2)
-                            if (parts.size == 2) {
-                                val mediaRelay = parts[0]
-                                val mediaRoom = parts[1]
-                                Log.i(TAG, "CallSetup: connecting to $mediaRelay room $mediaRoom")
-                                startCallInternal(mediaRelay, mediaRoom)
-                            }
-                        }
                         if (s.state == 2 && !audioStarted) {
                             startAudio()
                         }

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

@@ -219,7 +219,7 @@ fun InCallScreen(
 
                 // Mode toggle: Room vs Direct Call
                 val callMode by viewModel.callMode.collectAsState()
-                val signalState by viewModel.signalState.collectAsState()
+                val signalState by viewModel.signalState.collectAsState()  // "idle"/"registered"/"ringing"/etc
                 val targetFp by viewModel.targetFingerprint.collectAsState()
                 val incomingCallId by viewModel.incomingCallId.collectAsState()
                 val incomingCallerFp by viewModel.incomingCallerFp.collectAsState()
@@ -309,7 +309,7 @@ fun InCallScreen(
                     }
                 } else {
                     // ── Direct call mode ──
-                    if (signalState < 5) {
+                    if (signalState == "idle") {
                         // Not registered yet
                         SectionLabel("ALIAS")
                         OutlinedTextField(
@@ -333,7 +333,7 @@ fun InCallScreen(
                                 color = Color.White
                             )
                         }
-                    } else if (signalState == 5) {
+                    } else if (signalState == "registered" || signalState == "incoming") {
                         // Registered — show dial pad
                         Text(
                             "\u2705 Registered — waiting for calls",
@@ -403,8 +403,7 @@ fun InCallScreen(
                                 color = Color.White
                             )
                         }
-                    } else if (signalState == 6) {
-                        // Ringing
+                    } else if (signalState == "ringing") {
                         Text(
                             "\uD83D\uDD14 Ringing...",
                             color = Yellow,
@@ -412,11 +411,10 @@ fun InCallScreen(
                             textAlign = TextAlign.Center,
                             modifier = Modifier.fillMaxWidth()
                         )
-                    } else if (signalState == 7) {
-                        // Incoming call (state 7 also handled above in registered view)
+                    } else if (signalState == "setup") {
                         Text(
-                            "\uD83D\uDCDE Incoming call...",
-                            color = Green,
+                            "Connecting to call...",
+                            color = Accent,
                             style = MaterialTheme.typography.titleMedium,
                             textAlign = TextAlign.Center,
                             modifier = Modifier.fillMaxWidth()