feat: Android UI for direct 1:1 calling

- Mode toggle: "Room" vs "Direct Call" tabs on pre-connection screen
- Direct Call mode: Register button → registers on relay signal channel
- After registration: shows fingerprint dial pad + incoming call panel
- Incoming call: green Accept / red Reject buttons with caller info
- Ringing state display while waiting for callee
- CallSetup auto-connects to media room
- CallStats extended: sas_code, incoming_call_id/fp/alias fields
- CallViewModel: registerForCalls(), placeDirectCall(), answerIncomingCall()

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

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

@@ -43,6 +43,14 @@ data class CallStats(
     val roomParticipantCount: Int = 0,
     /** Participants in the room (fingerprint + optional alias). */
     val roomParticipants: List<RoomMember> = emptyList(),
+    /** SAS verification code (4-digit, null if not in a call). */
+    val sasCode: Int? = null,
+    /** Incoming call ID (or "relay|room" for CallSetup). */
+    val incomingCallId: String? = null,
+    /** Incoming caller's fingerprint. */
+    val incomingCallerFp: String? = null,
+    /** Incoming caller's alias. */
+    val incomingCallerAlias: String? = null,
 ) {
     /** Human-readable quality label. */
     val qualityLabel: String
@@ -87,7 +95,11 @@ data class CallStats(
                     peerCodec = obj.optString("peer_codec", ""),
                     autoMode = obj.optBoolean("auto_mode", false),
                     roomParticipantCount = obj.optInt("room_participant_count", 0),
-                    roomParticipants = parseParticipants(obj.optJSONArray("room_participants"))
+                    roomParticipants = parseParticipants(obj.optJSONArray("room_participants")),
+                    sasCode = if (obj.has("sas_code")) obj.optInt("sas_code") else null,
+                    incomingCallId = if (obj.isNull("incoming_call_id")) null else obj.optString("incoming_call_id", null),
+                    incomingCallerFp = if (obj.isNull("incoming_caller_fp")) null else obj.optString("incoming_caller_fp", null),
+                    incomingCallerAlias = if (obj.isNull("incoming_caller_alias")) null else obj.optString("incoming_caller_alias", null),
                 )
             } catch (e: Exception) {
                 CallStats()

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

@@ -132,6 +132,84 @@ class CallViewModel : ViewModel(), WzpCallback {
 
     private var statsJob: Job? = null
 
+    // ── Direct calling state ──
+    /** 0=room mode, 1=direct call mode */
+    private val _callMode = MutableStateFlow(0)
+    val callMode: StateFlow<Int> = _callMode.asStateFlow()
+
+    /** Target fingerprint for direct call */
+    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()
+
+    /** Incoming call info */
+    private val _incomingCallId = MutableStateFlow<String?>(null)
+    val incomingCallId: StateFlow<String?> = _incomingCallId.asStateFlow()
+
+    private val _incomingCallerFp = MutableStateFlow<String?>(null)
+    val incomingCallerFp: StateFlow<String?> = _incomingCallerFp.asStateFlow()
+
+    private val _incomingCallerAlias = MutableStateFlow<String?>(null)
+    val incomingCallerAlias: StateFlow<String?> = _incomingCallerAlias.asStateFlow()
+
+    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
+
+        viewModelScope.launch(Dispatchers.IO) {
+            val resolvedRelay = resolveToIp(relay) ?: relay
+            val result = engine?.startSignaling(resolvedRelay, seed, "", alias)
+            if (result == 0) {
+                _signalState.value = 5 // Registered
+                startStatsPolling()
+            } else {
+                _errorMessage.value = "Failed to register on relay"
+            }
+        }
+    }
+
+    /** Place a direct call to the target fingerprint */
+    fun placeDirectCall() {
+        val target = _targetFingerprint.value.trim()
+        if (target.isEmpty()) {
+            _errorMessage.value = "Enter a fingerprint to call"
+            return
+        }
+        engine?.placeCall(target)
+        _signalState.value = 6 // Ringing
+    }
+
+    /** Answer an incoming direct call */
+    fun answerIncomingCall(mode: Int = 2) {
+        val callId = _incomingCallId.value ?: return
+        engine?.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
+    }
+
     companion object {
         private const val TAG = "WzpCall"
         val DEFAULT_SERVERS = listOf(
@@ -418,6 +496,45 @@ class CallViewModel : ViewModel(), WzpCallback {
         startCallInternal()
     }
 
+    /** Start a call to a specific relay + room (used by direct call setup). */
+    private fun startCallInternal(relay: String, room: String) {
+        Log.i(TAG, "startCallDirect: relay=$relay room=$room")
+        try {
+            // Don't teardown — keep the signal connection alive
+            engine = WzpEngine(this)
+            engine!!.init()
+            engineInitialized = true
+            _callState.value = 1
+            _errorMessage.value = null
+            try { appContext?.let { CallService.start(it) } } catch (e: Exception) {
+                Log.w(TAG, "service start err: $e")
+            }
+            startStatsPolling()
+            viewModelScope.launch(kotlinx.coroutines.Dispatchers.IO) {
+                try {
+                    val seed = _seedHex.value
+                    val name = _alias.value
+                    val result = engine?.startCall(relay, room, seedHex = seed, alias = name, profile = _codecChoice.value) ?: -1
+                    CallService.onStopFromNotification = { stopCall() }
+                    if (result != 0) {
+                        _callState.value = 0
+                        _errorMessage.value = "Failed to connect to call room (code $result)"
+                        appContext?.let { CallService.stop(it) }
+                    }
+                } catch (e: Exception) {
+                    Log.e(TAG, "startCallDirect error", e)
+                    _callState.value = 0
+                    _errorMessage.value = "Engine error: ${e.message}"
+                    appContext?.let { CallService.stop(it) }
+                }
+            }
+        } catch (e: Exception) {
+            Log.e(TAG, "startCallDirect error", e)
+            _callState.value = 0
+            _errorMessage.value = "Engine error: ${e.message}"
+        }
+    }
+
     private fun startCallInternal() {
         val serverEntry = _servers.value[_selectedServer.value]
         val room = _roomName.value
@@ -571,6 +688,27 @@ class CallViewModel : ViewModel(), WzpCallback {
                         if (s.state != 0) {
                             _callState.value = s.state
                         }
+                        // Track signal state changes for direct calling
+                        if (s.state in 5..7) {
+                            _signalState.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

@@ -2,6 +2,7 @@ package com.wzp.ui.call
 
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
+import androidx.compose.ui.text.style.TextAlign
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -217,65 +218,211 @@ fun InCallScreen(
 
                 Spacer(modifier = Modifier.height(12.dp))
 
-                // Room
-                SectionLabel("ROOM")
-                OutlinedTextField(
-                    value = roomName,
-                    onValueChange = { viewModel.setRoomName(it) },
-                    singleLine = true,
-                    modifier = Modifier.fillMaxWidth()
-                )
+                // Mode toggle: Room vs Direct Call
+                val callMode by viewModel.callMode.collectAsState()
+                val signalState by viewModel.signalState.collectAsState()
+                val targetFp by viewModel.targetFingerprint.collectAsState()
+                val incomingCallId by viewModel.incomingCallId.collectAsState()
+                val incomingCallerFp by viewModel.incomingCallerFp.collectAsState()
+                val incomingCallerAlias by viewModel.incomingCallerAlias.collectAsState()
 
-                Spacer(modifier = Modifier.height(12.dp))
-
-                // Alias
-                SectionLabel("ALIAS")
-                OutlinedTextField(
-                    value = alias,
-                    onValueChange = { viewModel.setAlias(it) },
-                    singleLine = true,
-                    modifier = Modifier.fillMaxWidth()
-                )
-
-                Spacer(modifier = Modifier.height(12.dp))
-
-                // AEC + Settings
                 Row(
-                    verticalAlignment = Alignment.CenterVertically,
-                    modifier = Modifier.fillMaxWidth()
+                    modifier = Modifier.fillMaxWidth(),
+                    horizontalArrangement = Arrangement.spacedBy(8.dp)
                 ) {
-                    Checkbox(
-                        checked = aecEnabled,
-                        onCheckedChange = { viewModel.setAecEnabled(it) }
-                    )
-                    Text("OS ECHO CANCEL", color = TextDim, style = MaterialTheme.typography.labelSmall)
-                    Spacer(modifier = Modifier.weight(1f))
-                    Surface(
-                        onClick = onOpenSettings,
+                    Button(
+                        onClick = { viewModel.setCallMode(0) },
+                        modifier = Modifier.weight(1f).height(36.dp),
                         shape = RoundedCornerShape(8.dp),
-                        color = Color.Transparent,
-                        modifier = Modifier.size(36.dp)
-                    ) {
-                        Box(contentAlignment = Alignment.Center) {
-                            Text("\u2699", fontSize = 18.sp, color = TextDim)
-                        }
-                    }
+                        colors = ButtonDefaults.buttonColors(
+                            containerColor = if (callMode == 0) Accent else Color(0xFF333333)
+                        )
+                    ) { Text("Room", color = Color.White, fontSize = 13.sp) }
+                    Button(
+                        onClick = { viewModel.setCallMode(1) },
+                        modifier = Modifier.weight(1f).height(36.dp),
+                        shape = RoundedCornerShape(8.dp),
+                        colors = ButtonDefaults.buttonColors(
+                            containerColor = if (callMode == 1) Accent else Color(0xFF333333)
+                        )
+                    ) { Text("Direct Call", color = Color.White, fontSize = 13.sp) }
                 }
 
-                Spacer(modifier = Modifier.height(16.dp))
+                Spacer(modifier = Modifier.height(12.dp))
 
-                // Connect button
-                Button(
-                    onClick = { viewModel.startCall() },
-                    modifier = Modifier.fillMaxWidth().height(48.dp),
-                    shape = RoundedCornerShape(8.dp),
-                    colors = ButtonDefaults.buttonColors(containerColor = Accent)
-                ) {
-                    Text(
-                        "Connect",
-                        style = MaterialTheme.typography.titleMedium.copy(fontWeight = FontWeight.Bold),
-                        color = Color.White
+                if (callMode == 0) {
+                    // ── Room mode ──
+                    SectionLabel("ROOM")
+                    OutlinedTextField(
+                        value = roomName,
+                        onValueChange = { viewModel.setRoomName(it) },
+                        singleLine = true,
+                        modifier = Modifier.fillMaxWidth()
                     )
+
+                    Spacer(modifier = Modifier.height(12.dp))
+
+                    SectionLabel("ALIAS")
+                    OutlinedTextField(
+                        value = alias,
+                        onValueChange = { viewModel.setAlias(it) },
+                        singleLine = true,
+                        modifier = Modifier.fillMaxWidth()
+                    )
+
+                    Spacer(modifier = Modifier.height(12.dp))
+
+                    Row(
+                        verticalAlignment = Alignment.CenterVertically,
+                        modifier = Modifier.fillMaxWidth()
+                    ) {
+                        Checkbox(
+                            checked = aecEnabled,
+                            onCheckedChange = { viewModel.setAecEnabled(it) }
+                        )
+                        Text("OS ECHO CANCEL", color = TextDim, style = MaterialTheme.typography.labelSmall)
+                        Spacer(modifier = Modifier.weight(1f))
+                        Surface(
+                            onClick = onOpenSettings,
+                            shape = RoundedCornerShape(8.dp),
+                            color = Color.Transparent,
+                            modifier = Modifier.size(36.dp)
+                        ) {
+                            Box(contentAlignment = Alignment.Center) {
+                                Text("\u2699", fontSize = 18.sp, color = TextDim)
+                            }
+                        }
+                    }
+
+                    Spacer(modifier = Modifier.height(16.dp))
+
+                    Button(
+                        onClick = { viewModel.startCall() },
+                        modifier = Modifier.fillMaxWidth().height(48.dp),
+                        shape = RoundedCornerShape(8.dp),
+                        colors = ButtonDefaults.buttonColors(containerColor = Accent)
+                    ) {
+                        Text(
+                            "Connect",
+                            style = MaterialTheme.typography.titleMedium.copy(fontWeight = FontWeight.Bold),
+                            color = Color.White
+                        )
+                    }
+                } else {
+                    // ── Direct call mode ──
+                    if (signalState < 5) {
+                        // Not registered yet
+                        SectionLabel("ALIAS")
+                        OutlinedTextField(
+                            value = alias,
+                            onValueChange = { viewModel.setAlias(it) },
+                            singleLine = true,
+                            modifier = Modifier.fillMaxWidth()
+                        )
+
+                        Spacer(modifier = Modifier.height(16.dp))
+
+                        Button(
+                            onClick = { viewModel.registerForCalls() },
+                            modifier = Modifier.fillMaxWidth().height(48.dp),
+                            shape = RoundedCornerShape(8.dp),
+                            colors = ButtonDefaults.buttonColors(containerColor = Color(0xFF2196F3))
+                        ) {
+                            Text(
+                                "Register on Relay",
+                                style = MaterialTheme.typography.titleMedium.copy(fontWeight = FontWeight.Bold),
+                                color = Color.White
+                            )
+                        }
+                    } else if (signalState == 5) {
+                        // Registered — show dial pad
+                        Text(
+                            "\u2705 Registered — waiting for calls",
+                            color = Green,
+                            style = MaterialTheme.typography.bodyMedium
+                        )
+
+                        Spacer(modifier = Modifier.height(12.dp))
+
+                        // Incoming call notification
+                        if (incomingCallId != null && incomingCallerFp != null) {
+                            Surface(
+                                color = Color(0xFF1B5E20),
+                                shape = RoundedCornerShape(12.dp),
+                                modifier = Modifier.fillMaxWidth()
+                            ) {
+                                Column(modifier = Modifier.padding(16.dp)) {
+                                    Text(
+                                        "Incoming Call",
+                                        color = Color.White,
+                                        style = MaterialTheme.typography.titleMedium.copy(fontWeight = FontWeight.Bold)
+                                    )
+                                    Text(
+                                        "From: ${incomingCallerAlias ?: incomingCallerFp?.take(16) ?: "unknown"}",
+                                        color = Color.White.copy(alpha = 0.8f),
+                                        style = MaterialTheme.typography.bodySmall
+                                    )
+                                    Spacer(modifier = Modifier.height(12.dp))
+                                    Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                                        Button(
+                                            onClick = { viewModel.answerIncomingCall(2) },
+                                            colors = ButtonDefaults.buttonColors(containerColor = Green),
+                                            modifier = Modifier.weight(1f)
+                                        ) { Text("Accept", color = Color.White) }
+                                        Button(
+                                            onClick = { viewModel.rejectIncomingCall() },
+                                            colors = ButtonDefaults.buttonColors(containerColor = Red),
+                                            modifier = Modifier.weight(1f)
+                                        ) { Text("Reject", color = Color.White) }
+                                    }
+                                }
+                            }
+                            Spacer(modifier = Modifier.height(12.dp))
+                        }
+
+                        SectionLabel("CALL BY FINGERPRINT")
+                        OutlinedTextField(
+                            value = targetFp,
+                            onValueChange = { viewModel.setTargetFingerprint(it) },
+                            singleLine = true,
+                            placeholder = { Text("Paste fingerprint (xxxx:xxxx:...)") },
+                            modifier = Modifier.fillMaxWidth()
+                        )
+
+                        Spacer(modifier = Modifier.height(16.dp))
+
+                        Button(
+                            onClick = { viewModel.placeDirectCall() },
+                            modifier = Modifier.fillMaxWidth().height(48.dp),
+                            shape = RoundedCornerShape(8.dp),
+                            colors = ButtonDefaults.buttonColors(containerColor = Accent),
+                            enabled = targetFp.isNotBlank()
+                        ) {
+                            Text(
+                                "Call",
+                                style = MaterialTheme.typography.titleMedium.copy(fontWeight = FontWeight.Bold),
+                                color = Color.White
+                            )
+                        }
+                    } else if (signalState == 6) {
+                        // Ringing
+                        Text(
+                            "\uD83D\uDD14 Ringing...",
+                            color = Yellow,
+                            style = MaterialTheme.typography.titleMedium,
+                            textAlign = TextAlign.Center,
+                            modifier = Modifier.fillMaxWidth()
+                        )
+                    } else if (signalState == 7) {
+                        // Incoming call (state 7 also handled above in registered view)
+                        Text(
+                            "\uD83D\uDCDE Incoming call...",
+                            color = Green,
+                            style = MaterialTheme.typography.titleMedium,
+                            textAlign = TextAlign.Center,
+                            modifier = Modifier.fillMaxWidth()
+                        )
+                    }
                 }
 
                 errorMessage?.let { err ->