fix(terminal): fix new tab auto-focus and NaN error on data before layout (#14357)

- Fix new tab not auto-focusing: add FocusNode to TerminalView and
  request focus when tab is selected via tab state listener
- Fix NaN error when data arrives before terminal view layout: buffer
  output data until terminal view has valid dimensions, flush on first
  valid resize callback

Signed-off-by: fufesou <linlong1266@gmail.com>

flutter/lib/models/terminal_model.dart

@@ -24,6 +24,13 @@ class TerminalModel with ChangeNotifier {
   bool _disposed = false;
 
   final _inputBuffer = <String>[];
+  // Buffer for output data received before terminal view has valid dimensions.
+  // This prevents NaN errors when writing to terminal before layout is complete.
+  final _pendingOutputChunks = <String>[];
+  int _pendingOutputSize = 0;
+  static const int _kMaxOutputBufferChars = 8 * 1024;
+  // View ready state: true when terminal has valid dimensions, safe to write
+  bool _terminalViewReady = false;
 
   bool get isPeerWindows => parent.ffiModel.pi.platform == kPeerPlatformWindows;
 
@@ -74,6 +81,12 @@ class TerminalModel with ChangeNotifier {
         // This piece of code must be placed before the conditional check in order to initialize properly.
         onResizeExternal?.call(w, h, pw, ph);
 
+        // Mark terminal view as ready and flush any buffered output on first valid resize.
+        // Must be after onResizeExternal so the view layer has valid dimensions before flushing.
+        if (!_terminalViewReady) {
+          _markViewReady();
+        }
+
         if (_terminalOpened) {
           // Notify remote terminal of resize
           try {
@@ -141,7 +154,7 @@ class TerminalModel with ChangeNotifier {
       debugPrint('[TerminalModel] Error calling sessionOpenTerminal: $e');
       // Optionally show error to user
       if (e is TimeoutException) {
-        terminal.write('Failed to open terminal: Connection timeout\r\n');
+        _writeToTerminal('Failed to open terminal: Connection timeout\r\n');
       }
     }
   }
@@ -283,7 +296,7 @@ class TerminalModel with ChangeNotifier {
             }));
       }
     } else {
-      terminal.write('Failed to open terminal: $message\r\n');
+      _writeToTerminal('Failed to open terminal: $message\r\n');
     }
   }
 
@@ -327,29 +340,83 @@ class TerminalModel with ChangeNotifier {
           return;
         }
 
-        terminal.write(text);
+        _writeToTerminal(text);
       } catch (e) {
         debugPrint('[TerminalModel] Failed to process terminal data: $e');
       }
     }
   }
 
+  /// Write text to terminal, buffering if the view is not yet ready.
+  /// All terminal output should go through this method to avoid NaN errors
+  /// from writing before the terminal view has valid layout dimensions.
+  void _writeToTerminal(String text) {
+    if (!_terminalViewReady) {
+      // If a single chunk exceeds the cap, keep only its tail.
+      // Note: truncation may split a multi-byte ANSI escape sequence,
+      // which can cause a brief visual glitch on flush. This is acceptable
+      // because it only affects the pre-layout buffering window and the
+      // terminal will self-correct on subsequent output.
+      if (text.length >= _kMaxOutputBufferChars) {
+        final truncated =
+            text.substring(text.length - _kMaxOutputBufferChars);
+        _pendingOutputChunks
+          ..clear()
+          ..add(truncated);
+        _pendingOutputSize = truncated.length;
+      } else {
+        _pendingOutputChunks.add(text);
+        _pendingOutputSize += text.length;
+        // Drop oldest chunks if exceeds limit (whole chunks to preserve ANSI sequences)
+        while (_pendingOutputSize > _kMaxOutputBufferChars &&
+            _pendingOutputChunks.length > 1) {
+          final removed = _pendingOutputChunks.removeAt(0);
+          _pendingOutputSize -= removed.length;
+        }
+      }
+      return;
+    }
+    terminal.write(text);
+  }
+
+  void _flushOutputBuffer() {
+    if (_pendingOutputChunks.isEmpty) return;
+    debugPrint(
+        '[TerminalModel] Flushing $_pendingOutputSize buffered chars (${_pendingOutputChunks.length} chunks)');
+    for (final chunk in _pendingOutputChunks) {
+      terminal.write(chunk);
+    }
+    _pendingOutputChunks.clear();
+    _pendingOutputSize = 0;
+  }
+
+  /// Mark terminal view as ready and flush buffered output.
+  void _markViewReady() {
+    if (_terminalViewReady) return;
+    _terminalViewReady = true;
+    _flushOutputBuffer();
+  }
+
   void _handleTerminalClosed(Map<String, dynamic> evt) {
     final int exitCode = evt['exit_code'] ?? 0;
-    terminal.write('\r\nTerminal closed with exit code: $exitCode\r\n');
+    _writeToTerminal('\r\nTerminal closed with exit code: $exitCode\r\n');
     _terminalOpened = false;
     notifyListeners();
   }
 
   void _handleTerminalError(Map<String, dynamic> evt) {
     final String message = evt['message'] ?? 'Unknown error';
-    terminal.write('\r\nTerminal error: $message\r\n');
+    _writeToTerminal('\r\nTerminal error: $message\r\n');
   }
 
   @override
   void dispose() {
     if (_disposed) return;
     _disposed = true;
+    // Clear buffers to free memory
+    _inputBuffer.clear();
+    _pendingOutputChunks.clear();
+    _pendingOutputSize = 0;
     // Terminal cleanup is handled server-side when service closes
     super.dispose();
   }