fix: Use Alt+U/Alt+R for undo/redo, fix state tracking

- Changed undo/redo keys to Alt+U and Alt+R (meta keys work in urwid)
- Fixed undo logic: now saves state BEFORE edit happens, not after
- Added duplicate state prevention
- Simplified the tracking logic

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/smarttools/ui_urwid.py

@@ -345,11 +345,9 @@ class UndoableEdit(urwid.Edit):
     """A multiline Edit with undo/redo support.
 
     Features:
-    - Undo with Ctrl+U (up to 50 states)
-    - Redo with Ctrl+R
+    - Undo with Alt+U (up to 50 states)
+    - Redo with Alt+R
     - Tab passes through for focus cycling
-
-    Note: Ctrl+Z cannot be used as it's the Unix suspend signal (SIGTSTP).
     """
 
     MAX_UNDO = 50  # Maximum undo history size
@@ -358,40 +356,40 @@ class UndoableEdit(urwid.Edit):
         super().__init__(*args, **kwargs)
         self._undo_stack = []  # List of (text, cursor_pos) tuples
         self._redo_stack = []
-        self._last_saved_text = self.edit_text  # Track for change detection
 
     def keypress(self, size, key):
         if key in ('tab', 'shift tab'):
             return key
 
-        # Save state before any editing operation (for undo)
-        current_text = self.edit_text
-        if current_text != self._last_saved_text:
-            self._save_undo_state(self._last_saved_text, self.edit_pos)
-            self._last_saved_text = current_text
-
-        # Handle undo (Ctrl+U) - can't use Ctrl+Z as it's Unix suspend signal
-        if key == 'ctrl u':
+        # Handle undo (Alt+U or meta u)
+        if key in ('meta u', 'alt u'):
             self._undo()
             return None
 
-        # Handle redo (Ctrl+R)
-        if key == 'ctrl r':
+        # Handle redo (Alt+R or meta r)
+        if key in ('meta r', 'alt r'):
             self._redo()
             return None
 
+        # Save current state BEFORE the edit for undo
+        old_text = self.edit_text
+        old_pos = self.edit_pos
+
+        # Let the parent handle the keypress
         result = super().keypress(size, key)
 
-        # After edit, check if text changed and save for potential undo
-        new_text = self.edit_text
-        if new_text != self._last_saved_text:
+        # If text changed, save the old state to undo stack
+        if self.edit_text != old_text:
+            self._save_undo_state(old_text, old_pos)
             self._redo_stack.clear()  # Clear redo on new edit
-            self._last_saved_text = new_text
 
         return result
 
     def _save_undo_state(self, text, pos):
-        """Save current state to undo stack."""
+        """Save state to undo stack."""
+        # Don't save duplicate states
+        if self._undo_stack and self._undo_stack[-1][0] == text:
+            return
         if len(self._undo_stack) >= self.MAX_UNDO:
             self._undo_stack.pop(0)
         self._undo_stack.append((text, pos))
@@ -408,7 +406,6 @@ class UndoableEdit(urwid.Edit):
         text, pos = self._undo_stack.pop()
         self.set_edit_text(text)
         self.set_edit_pos(min(pos, len(text)))
-        self._last_saved_text = text
 
     def _redo(self):
         """Restore state from redo stack."""
@@ -422,7 +419,6 @@ class UndoableEdit(urwid.Edit):
         text, pos = self._redo_stack.pop()
         self.set_edit_text(text)
         self.set_edit_pos(min(pos, len(text)))
-        self._last_saved_text = text
 
 
 class DOSScrollBar(urwid.WidgetWrap):
@@ -1687,7 +1683,7 @@ class SmartToolsUI:
         default_file = existing.code_file if existing and existing.code_file else f"{default_output_var}.py"
         file_edit = urwid.Edit(('label', "File: "), default_file)
 
-        # Multiline code editor with undo/redo (Ctrl+U / Ctrl+R)
+        # Multiline code editor with undo/redo (Alt+U / Alt+R)
         default_code = existing.code if existing else f"{default_output_var} = input.upper()"
         code_edit = UndoableEdit(
             edit_text=default_code,