feat(it0_app): add PTT mode to agent call page

- Default to PTT (push-to-talk) on call connect: mic muted until user holds button
- Toggle switch between PTT and free voice mode in active call controls
- PTT button: press-and-hold unmutes mic, release mutes again
- Voice message bubble (waveform + duration) appears after each PTT send
- Mute button hidden in PTT mode (mic controlled by PTT button)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

it0_app/lib/features/agent_call/presentation/pages/agent_call_page.dart

@@ -72,6 +72,12 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
   final List<_CallMessage> _messages = [];
   final ScrollController _scrollController = ScrollController();
 
+  // PTT (Push-to-Talk) mode
+  bool _isPttMode = true;
+  bool _pttRecording = false;
+  final Stopwatch _pttStopwatch = Stopwatch();
+  Timer? _pttTimer;
+
   @override
   void initState() {
     super.initState();
@@ -207,8 +213,8 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
         ),
       );
 
-      // 5. Enable microphone (publishes local audio track)
+      // 5. Enable microphone — muted by default in PTT mode
-      await _room!.localParticipant?.setMicrophoneEnabled(true);
+      await _room!.localParticipant?.setMicrophoneEnabled(!_isPttMode);
 
       // 6. Start duration timer
       _stopwatch.start();
@@ -304,6 +310,66 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
     setState(() {});
   }
 
+  // ---------------------------------------------------------------------------
+  // PTT (Push-to-Talk)
+  // ---------------------------------------------------------------------------
+
+  void _startPtt() {
+    if (!_isPttMode || _phase != _CallPhase.active || _pttRecording) return;
+    _room?.localParticipant?.setMicrophoneEnabled(true);
+    _pttStopwatch
+      ..reset()
+      ..start();
+    _pttTimer = Timer.periodic(const Duration(milliseconds: 50), (_) {
+      if (mounted) setState(() {});
+    });
+    setState(() => _pttRecording = true);
+  }
+
+  void _stopPtt() {
+    if (!_pttRecording) return;
+    _room?.localParticipant?.setMicrophoneEnabled(false);
+    _pttStopwatch.stop();
+    _pttTimer?.cancel();
+    _pttTimer = null;
+    final elapsed = _pttStopwatch.elapsed;
+    if (elapsed.inMilliseconds >= 300) {
+      _messages.add(_CallMessage(
+        text: '',
+        isUser: true,
+        timestamp: DateTime.now(),
+        isVoice: true,
+        voiceDurationMs: elapsed.inMilliseconds,
+      ));
+      _scrollToBottom();
+    }
+    setState(() => _pttRecording = false);
+  }
+
+  void _togglePttMode() {
+    if (_pttRecording) _stopPtt();
+    final newPtt = !_isPttMode;
+    setState(() => _isPttMode = newPtt);
+    if (_phase == _CallPhase.active) {
+      _room?.localParticipant?.setMicrophoneEnabled(!newPtt);
+    }
+  }
+
+  String _formatPttDuration() {
+    final ms = _pttStopwatch.elapsedMilliseconds;
+    final secs = ms ~/ 1000;
+    final tenths = (ms % 1000) ~/ 100;
+    return '$secs.$tenths"';
+  }
+
+  String _formatVoiceDuration(int ms) {
+    final secs = ms ~/ 1000;
+    if (secs < 60) return '${secs}s';
+    final mins = secs ~/ 60;
+    final s = secs % 60;
+    return '$mins:${s.toString().padLeft(2, '0')}';
+  }
+
   void _scrollToBottom() {
     WidgetsBinding.instance.addPostFrameCallback((_) {
       if (_scrollController.hasClients) {
@@ -658,6 +724,10 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
             ),
           if (_phase == _CallPhase.active)
             _agentState == 'thinking' ? _buildThinkingDots() : _buildWaveform(),
+          if (_phase == _CallPhase.active && _isPttMode) ...[
+            const SizedBox(height: 28),
+            _buildPttButton(),
+          ],
           const Spacer(flex: 3),
           _buildControls(),
           const SizedBox(height: 48),
@@ -774,6 +844,7 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
   }
 
   Widget _buildMessageBubble(_CallMessage msg) {
+    if (msg.isVoice) return _buildVoiceMessageBubble(msg);
     final isUser = msg.isUser;
     return Padding(
       padding: const EdgeInsets.only(bottom: 12),
@@ -1168,6 +1239,115 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
     );
   }
 
+  /// Large press-and-hold PTT button shown in call mode.
+  Widget _buildPttButton() {
+    return Listener(
+      onPointerDown: (_) => _startPtt(),
+      onPointerUp: (_) => _stopPtt(),
+      onPointerCancel: (_) => _stopPtt(),
+      child: AnimatedContainer(
+        duration: const Duration(milliseconds: 120),
+        width: _pttRecording ? 100 : 84,
+        height: _pttRecording ? 100 : 84,
+        decoration: BoxDecoration(
+          shape: BoxShape.circle,
+          color: _pttRecording
+              ? AppColors.error.withOpacity(0.15)
+              : AppColors.primary.withOpacity(0.12),
+          border: Border.all(
+            color: _pttRecording ? AppColors.error : AppColors.primary,
+            width: _pttRecording ? 3 : 2,
+          ),
+          boxShadow: _pttRecording
+              ? [
+                  BoxShadow(
+                    color: AppColors.error.withOpacity(0.35),
+                    blurRadius: 24,
+                    spreadRadius: 4,
+                  )
+                ]
+              : [],
+        ),
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.center,
+          children: [
+            Icon(
+              _pttRecording ? Icons.mic : Icons.mic_none,
+              size: _pttRecording ? 36 : 30,
+              color: _pttRecording ? AppColors.error : AppColors.primary,
+            ),
+            const SizedBox(height: 2),
+            Text(
+              _pttRecording ? _formatPttDuration() : '按住说话',
+              style: TextStyle(
+                fontSize: _pttRecording ? 12 : 11,
+                color: _pttRecording ? AppColors.error : AppColors.textSecondary,
+                fontWeight: _pttRecording ? FontWeight.w600 : FontWeight.normal,
+              ),
+            ),
+          ],
+        ),
+      ),
+    );
+  }
+
+  /// Voice message bubble: decorative waveform + duration.
+  Widget _buildVoiceMessageBubble(_CallMessage msg) {
+    final rand = Random(msg.voiceDurationMs ^ msg.timestamp.millisecondsSinceEpoch);
+    final bars = List.generate(18, (_) => 0.15 + rand.nextDouble() * 0.85);
+    return Padding(
+      padding: const EdgeInsets.only(bottom: 12),
+      child: Row(
+        mainAxisAlignment: MainAxisAlignment.end,
+        children: [
+          Container(
+            padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 10),
+            decoration: BoxDecoration(
+              color: AppColors.primary.withOpacity(0.15),
+              borderRadius: const BorderRadius.only(
+                topLeft: Radius.circular(16),
+                topRight: Radius.circular(16),
+                bottomLeft: Radius.circular(16),
+                bottomRight: Radius.circular(4),
+              ),
+            ),
+            child: Row(
+              mainAxisSize: MainAxisSize.min,
+              crossAxisAlignment: CrossAxisAlignment.center,
+              children: [
+                const Icon(Icons.mic, size: 16, color: AppColors.primary),
+                const SizedBox(width: 6),
+                Row(
+                  crossAxisAlignment: CrossAxisAlignment.center,
+                  children: bars
+                      .map((h) => Container(
+                            width: 3,
+                            height: 6 + h * 18,
+                            margin: const EdgeInsets.symmetric(horizontal: 1),
+                            decoration: BoxDecoration(
+                              color: AppColors.primary.withOpacity(0.65),
+                              borderRadius: BorderRadius.circular(1.5),
+                            ),
+                          ))
+                      .toList(),
+                ),
+                const SizedBox(width: 6),
+                Text(
+                  _formatVoiceDuration(msg.voiceDurationMs),
+                  style: const TextStyle(
+                    color: AppColors.textSecondary,
+                    fontSize: 12,
+                  ),
+                ),
+              ],
+            ),
+          ),
+          const SizedBox(width: 8),
+        ],
+      ),
+    );
+  }
+
   Widget _buildControls() {
     switch (_phase) {
       case _CallPhase.ringing:
@@ -1197,6 +1377,13 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
         return Row(
           mainAxisAlignment: MainAxisAlignment.center,
           children: [
+            _CircleButton(
+              icon: _isPttMode ? Icons.touch_app : Icons.wifi_tethering,
+              label: _isPttMode ? 'PTT' : '自由',
+              isActive: _isPttMode,
+              onTap: _togglePttMode,
+            ),
+            const SizedBox(width: 16),
             _CircleButton(
               icon: _isInputExpanded ? Icons.keyboard_hide : Icons.keyboard,
               label: _isInputExpanded ? '收起' : '键盘',
@@ -1204,6 +1391,7 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
               onTap: () => setState(() => _isInputExpanded = !_isInputExpanded),
             ),
             const SizedBox(width: 16),
+            if (!_isPttMode) ...[
               _CircleButton(
                 icon: _isMuted ? Icons.mic_off : Icons.mic,
                 label: _isMuted ? '取消静音' : '静音',
@@ -1211,6 +1399,7 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
                 onTap: _toggleMute,
               ),
               const SizedBox(width: 16),
+            ],
             FloatingActionButton(
               heroTag: 'end',
               backgroundColor: AppColors.error,
@@ -1240,6 +1429,8 @@ class _AgentCallPageState extends ConsumerState<AgentCallPage>
     _scrollController.dispose();
     _durationTimer?.cancel();
     _waveTimer?.cancel();
+    _pttTimer?.cancel();
+    _pttStopwatch.stop();
     _waveController.dispose();
     _thinkingController.dispose();
     _stopwatch.stop();
@@ -1259,12 +1450,16 @@ class _CallMessage {
   final bool isUser;
   final DateTime timestamp;
   final List<ChatAttachment>? attachments;
+  final bool isVoice;
+  final int voiceDurationMs;
 
   _CallMessage({
     required this.text,
     required this.isUser,
     required this.timestamp,
     this.attachments,
+    this.isVoice = false,
+    this.voiceDurationMs = 0,
   });
 }