fix: proper terminal buffer save/restore with full pyte screen state

Save complete pyte screen state (characters, colors, attributes,
cursor position, modes) via pickle serialization instead of just
plain text. Restore via direct buffer manipulation + full redraw.
Fixes broken/garbled layout when switching between servers.

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

gui/widgets/terminal_widget.py

@@ -362,21 +362,81 @@ class TerminalWidget(tk.Frame):
         return self._cols, self._rows
 
     def get_current_buffer(self) -> bytes:
-        """Export current pyte screen content as ANSI bytes for session pool preservation."""
-        screen = self._screen
-        lines = []
-        for row in range(screen.lines):
-            line = screen.buffer[row]
-            chars = []
-            for col in range(screen.columns):
-                chars.append(line[col].data)
-            # Strip trailing spaces
-            text = "".join(chars).rstrip()
-            lines.append(text)
-        # Remove trailing empty lines
-        while lines and not lines[-1]:
-            lines.pop()
-        return "\n".join(lines).encode("utf-8")
+        """Export full pyte screen state as serialized data for session pool."""
+        import pickle
+
+        screen_state = {
+            'buffer': {},
+            'cursor_x': self._screen.cursor.x,
+            'cursor_y': self._screen.cursor.y,
+            'cursor_attrs': self._screen.cursor.attrs,
+            'cursor_hidden': self._screen.cursor.hidden,
+            'mode': self._screen.mode.copy(),
+            'columns': self._screen.columns,
+            'lines': self._screen.lines,
+        }
+
+        for y in range(self._screen.lines):
+            line_dict = {}
+            for x in range(self._screen.columns):
+                c = self._screen.buffer[y][x]
+                line_dict[x] = {
+                    'data': c.data, 'fg': c.fg, 'bg': c.bg,
+                    'bold': c.bold, 'italics': c.italics,
+                    'underscore': c.underscore, 'reverse': c.reverse,
+                    'strikethrough': c.strikethrough, 'width': c.width,
+                }
+            screen_state['buffer'][y] = line_dict
+
+        return pickle.dumps(screen_state)
+
+    def restore_buffer(self, buffer_data: bytes):
+        """Restore full pyte screen state from serialized data."""
+        import pickle
+
+        try:
+            state = pickle.loads(buffer_data)
+            if not isinstance(state, dict) or 'buffer' not in state:
+                return
+
+            cols, rows = self._screen.columns, self._screen.lines
+            self._screen.reset()
+            self._screen.resize(rows, cols)
+
+            for y, line_dict in state['buffer'].items():
+                if y >= self._screen.lines:
+                    continue
+                for x, cd in line_dict.items():
+                    if x >= self._screen.columns:
+                        continue
+                    ch = self._screen.buffer[y][x]
+                    ch.data = cd['data']
+                    ch.fg = cd['fg']
+                    ch.bg = cd['bg']
+                    ch.bold = cd['bold']
+                    ch.italics = cd['italics']
+                    ch.underscore = cd['underscore']
+                    ch.reverse = cd['reverse']
+                    ch.strikethrough = cd['strikethrough']
+                    ch.width = cd['width']
+
+            self._screen.cursor.x = state.get('cursor_x', 0)
+            self._screen.cursor.y = state.get('cursor_y', 0)
+            if 'cursor_attrs' in state:
+                self._screen.cursor.attrs = state['cursor_attrs']
+            if 'cursor_hidden' in state:
+                self._screen.cursor.hidden = state['cursor_hidden']
+            if 'mode' in state:
+                self._screen.mode.clear()
+                self._screen.mode.update(state['mode'])
+
+            # Force full redraw
+            self._screen.dirty.update(range(self._screen.lines))
+            self._prev_buffer.clear()
+            self._render()
+
+        except Exception:
+            self.reset()
 
     # ── Rendering ──────────────────────────────────────────────────────────