MCP Debugger

# Breakpoint Validation - Summary of Findings ## The Problem (User Perspective) 1. **User**: "Set breakpoint on file X at line 5" 2. **System**: "Success! Breakpoint set." 3. **User**: "Set breakpoint on file Y at line 10" 4. **System**: "Success! Breakpoint set." 5. **User**: "Start debugging" 6. **System**: "Failed to spawn launcher: [WinError 267] The directory name is invalid" 7. **User**: "What went wrong? Which file? Why?" ## Why This Happens ### The Architecture ``` User calls set_breakpoint ↓ mcp-debugger stores breakpoint locally ↓ Returns "success" (debugpy not running yet) ↓ User calls start_debugging ↓ mcp-debugger starts debugpy ↓ Sends all breakpoints to debugpy ↓ debugpy validates files ↓ If any file missing → CRASH with cryptic error ``` ### The Timing Problem - **When we need validation**: When `set_breakpoint` is called - **When debugpy provides validation**: When `start_debugging` is called - **Result**: Too late to help ## What We Discovered 1. **debugpy DOES provide helpful messages**: - "Breakpoint in file that does not exist." - But only after debugging starts 2. **The implemented fix captures these messages**: - Added infrastructure to store them - But they arrive after the crash 3. **Users never see the helpful messages**: - Session crashes first - Cryptic error shown instead ## Why The Fix Doesn't Work The fix assumes: ``` set_breakpoint → debugpy validates → we capture message → show user ``` Reality is: ``` set_breakpoint → no debugpy yet → no validation → generic success start_debugging → debugpy validates → session crashes → user sees cryptic error ``` ## What Would Actually Fix This Since we can't get validation from debugpy at the right time: 1. **Option 1**: Validate file existence in mcp-debugger when `set_breakpoint` is called 2. **Option 2**: Better error handling to identify which file caused the crash 3. **Option 3**: Both of the above ## Bottom Line - **The investigation was correct**: debugpy provides messages - **The conclusion was wrong**: These messages can't solve the UX problem - **The fix is ineffective**: It captures messages that arrive too late - **The problem remains**: Users get cryptic errors with no actionable feedback