# Session 2025-10-27: Error Handling and Continue Button Debugging

## Status: ✅ COMPLETED

## Summary

Fixed multiple issues with runtime error handling, Continue button functionality, and UI feedback when errors occur. All issues resolved and tested.

## Issues Fixed

### 1. FOR Loop Stack Corruption (COMPLETED)
**Problem:** Stack showed 23 duplicate FOR loops instead of 2 when hitting NEXT error.

**Root Cause:** NEXT statements with reversed variable names (NEXT x% when should be NEXT y%) caused stack corruption. NEXT would pop wrong loop, then FOR would push duplicate entries.

**Fix Applied:**
- Added validation in `_execute_next_single()` to verify loop variable is on top of stack
- Added validation in `push_for_loop()` to prevent duplicate variable loops
- Clear error: "NEXT x% without FOR - found FOR y% loop instead (improper nesting)"

**Files Modified:**
- `src/interpreter.py` (lines 1445-1459)
- `src/runtime.py` (lines 802-806)

### 2. Continue Button Not Working After Errors (COMPLETED)
**Problem:** Clicking Continue after runtime error did nothing. Status showed "Not paused".

**Root Cause:** Runtime errors caught by exception handler didn't set `paused_at_breakpoint = True`.

**Fix Applied:**
- Set `paused_at_breakpoint = True` in exception handler
- Re-parse program from editor when continuing from error
- Build line_table and line_order from ProgramNode.lines
- Clear error state and resume execution

**Files Modified:**
- `src/ui/tk_ui.py` (lines 663-730, 2287, 2707-721)

### 3. Red ? Error Markers Not Showing on Runtime Errors (COMPLETED)
**Problem:** Syntax errors showed red ?, but runtime errors didn't.

**Fix Applied:**
- Call `editor_text.set_error()` in exception handler
- Show red ? on error line with error message tooltip

**Files Modified:**
- `src/ui/tk_ui.py` (lines 2326-2335)

### 4. Immediate Mode Status Always "Ok" (COMPLETED)
**Problem:** Status indicator showed green "Ok" even when at error/breakpoint.

**Fix Applied:**
- Show "Error" (red) when status == 'error'
- Show "Breakpoint" (orange) when status == 'at_breakpoint'
- Show "Paused" (orange) when status == 'paused'
- Show "Ok" (green) only when actually ready

**Files Modified:**
- `src/ui/tk_ui.py` (lines 2663-2686)

### 5. Yellow Highlight Issues (COMPLETED)
**Problem:** Yellow statement highlight blocked text selection and left "half yellow line" when editing.

**Fix Applied:**
- Clear yellow highlight on any key press
- Clear yellow highlight on mouse click
- Allows normal text selection and editing

**Files Modified:**
- `src/ui/tk_ui.py` (lines 1846-1849, 1716-1718)

### 6. Red ? Not Clearing When Line Fixed (COMPLETED)
**Problem:** After editing error line, red ? stayed until arrow key movement.

**Fix Applied:**
- Validate syntax on mouse click (not just arrow keys)
- Red ? clears when clicking away from fixed line

**Files Modified:**
- `src/ui/tk_ui.py` (lines 1721-1722)

## Infrastructure Improvements

### Version Tracking System (COMPLETED)
**Problem:** No way to verify user had latest code when debugging.

**Solution:**
- Created `src/version.py` with VERSION constant
- Added version to all debug error output
- Created `checkpoint.sh` script to automate version increment + commit + push
- Updated CLAUDE.md with checkpoint workflow

**Files Created:**
- `src/version.py`
- `checkpoint.sh`
- `mbasic_debug.sh` (stderr to file with tee)

### Debug Output System (COMPLETED)
**Problem:** Debug output not reliably visible.

**Solution:**
- Re-enabled MBASIC_DEBUG=1 in .bashrc permanently
- Added MBASIC_DEBUG_LEVEL for verbosity control (1=errors, 2=verbose)
- Created mbasic_debug.sh wrapper with tee (visible to both user and Claude)
- All debug errors now show version number

**Files Modified:**
- `src/debug_logger.py` (added get_debug_level, version in output)
- `src/runtime.py` (use debug_log with levels)
- `.claude/CLAUDE.md` (documented debug system)

## Test Results

All features tested and working:

✅ FOR loop stack corruption properly detected with clear error
✅ Continue button works after editing error lines
✅ Red ? appears on runtime errors
✅ Red ? clears when line is fixed
✅ Immediate Mode status shows "Error" not "Ok"
✅ Yellow highlight clears on typing or clicking
✅ Text selection visible on error lines
✅ Version tracking shows in debug output

## Commits in This Session

1. Fix FOR loop stack corruption with improper NEXT nesting
2. Enable Continue button to work after runtime errors
3. Fix Continue after edit and add red ? error markers
4. Add debug logging for Continue button and error highlighting
5. Fix error handling in exception handler to enable Continue
6. Add debug level system to separate errors from verbose output
7. Fix missing tkinter import in _menu_continue
8. Show actual state in Immediate Mode indicator
9. Clear yellow highlight when user starts editing
10. Validate syntax when clicking on different line
11. Fix debug log accessing non-existent program.line_table attribute
12. Clear yellow highlight on mouse click to allow text selection to be visible
13. Add version system to track code in debug output
14. Update CLAUDE.md with clear git commit workflow steps
15. Add checkpoint script to automate version increment and git workflow

## Final Version: 1.0.5

## User Workflow Now

When runtime error occurs:
1. Program shows red ? on error line with error message
2. Yellow highlight shows error statement
3. Immediate Mode shows "Error" (red)
4. Status: "Error at line 70 - Edit and Continue, or Stop"
5. User edits the line to fix error
6. User clicks Continue (Ctrl+G) or clicks away (red ? clears)
7. Program re-parses and resumes execution

Everything works as expected in traditional BASIC debugging!
