Add session summary for GTK4 frontend progress

Documents all fixes completed today and next steps.

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

CONTINUATION_NOTES.md

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+# GTK4 Frontend Session Summary (2025-11-27)
+
+## ✅ COMPLETED - Fully Functional Basic Editing!
+
+### What Works
+- ✅ Text input and rendering (Pango-based)
+- ✅ **Cursor visible and correctly positioned** (bright green 2px bar)
+- ✅ All keybindings working (C-n, C-p, C-f, C-b, C-a, C-e, etc.)
+- ✅ C-x C-c quits the application
+- ✅ Return creates new lines
+- ✅ Backspace/Delete work correctly
+- ✅ Theme switching (C-x t v/e/d)
+- ✅ Event system and redraws working
+
+### Key Fixes Made
+1. **Cursor Position** - Fixed Y-coordinate to align with text baseline
+2. **Keybinding C-x C-c** - Changed from show_config to quit()
+3. **Event Callbacks** - Proper cleanup before view destruction
+4. **Self-Insert** - Fallback for unbound printable characters
+
+## ⚠️ REMAINING ISSUE
+
+**Exit Crash (Double-Free)**
+- Occurs when closing window or quitting with C-x C-c
+- Error: `malloc: double free for ptr 0x...`
+- Editor is fully usable, only crashes on exit
+- May be related to GTK window/application cleanup order
+
+## 📁 Recent Commits
+```
+84fac4c Update STATUS.md: cursor and keybindings working
+21ca03c GTK4 Frontend: Fix cursor alignment and keybindings  
+e44c014 Fix GTK keybindings: Add fallback handlers
+55f21bd Fix GTK4 exit crash and character rendering issues
+```
+
+## 🔜 Next Steps (Future Session)
+
+1. **Fix Exit Crash** (Priority)
+   - Investigate GTK window/application destruction
+   - May need to adjust cleanup order in destructor
+   - Check for any remaining callback references
+
+2. **Implement Scrolling**
+   - Viewport offset for large files
+   - Update visible_line_range handling
+
+3. **Window Splits**
+   - Use Gtk::Paned or Gtk::Grid
+   - Multiple buffer views
+
+## 🏃 Quick Start Next Session
+```bash
+./build/lumacs  # Test current state
+# Editor works perfectly, just crashes on exit
+```
+
+Branch: `feature/gui-frontend`
+All changes committed and documented.