Full Stack Debugger

Full Stack Debugger

Overview

The Full Stack Debugger enables systematic debugging of issues across the entire application stack (UI/Frontend, Backend/API, Database/State). It combines browser testing, log analysis, code examination, and automated server restart/verification to iteratively identify and fix issues one at a time until the system is fully operational.

This skill uses a proven workflow: Detection → Analysis → Fix → Restart → Verification → Iteration to systematically resolve issues that developers encounter during development and testing.

When to Use This Skill

Trigger this skill when observing:

• Error states in the UI (dashboard, buttons failing, status showing errors)
• Repeated failures in backend logs (task execution failures, import errors, database errors)
• Unexpected database state (rows showing failed status when they should succeed)
• API endpoints returning errors or unexpected responses
• Services failing to initialize or process tasks
• Cascading failures across multiple components

Debugging Workflow

Phase 1: Detection

Detect errors from multiple sources:

Browser UI Detection:

• Navigate to the affected page/feature in the browser
• Check for error messages, red warning states, or disabled functionality
• Read console error messages using DevTools
• Note the specific UI state and what action triggered the error

Backend Log Detection:

• Query recent error logs using tail -200 /path/to/logs/errors.log
• Search for error patterns related to the issue using grep
• Note error timestamps, error messages, and stack traces
• Look for repeated errors (indicates systemic issue)

Database State Detection:

• Query the database directly using sqlite3
• Check status of recent tasks, transactions, or records
• Look for failed, incomplete, or error states
• Note which records are affected and what their states are

Example: When debugging a scheduler failure:

1. Navigate to System Health dashboard
2. Observe scheduler showing "0 done" or "X failed"
3. Check /logs/errors.log for error messages
4. Query queue_tasks table to see failed task records

Phase 2: Analysis

Analyze root causes by reading code and logs:

Code Analysis:

• Read the error file/module indicated in error stack traces
• Check imports - look for missing from X import Y statements
• Check class names - verify instantiation matches actual class names
• Look for syntax errors - unmatched quotes, unclosed parentheses
• Check function signatures - ensure payloads match expected parameters
• Read reference documentation (references/common_errors.md) for error patterns

Log Analysis:

• Extract error messages from logs
• Look for patterns like 'optional' (missing import), unterminated string (syntax error), 'attribute' (wrong class name)
• Trace error propagation backward to find the originating issue
• Check timestamps - multiple errors at same time indicate batch failure

API/Payload Analysis:

• Check what payload the API is sending to task handlers
• Read the task handler code to see what fields it expects
• Compare actual payload vs expected payload
• Look for missing required fields

Example: When debugging "name 'Optional' is not defined":

1. Find the file mentioned in error (analysis_executor.py)
2. Read the imports section
3. Notice Optional is used but not imported
4. Check line 14: from typing import Dict, List, Any - missing Optional
5. Fix: Add Optional to the import statement

Phase 3: Fix (One Issue at a Time)

Apply fixes one issue per iteration:

Before Fixing:

• Verify this is the first/next issue to fix
• Read the relevant code section carefully
• Use the fix patterns from references/fix_templates.md

Common Fix Patterns:

• Missing imports: Add to import statement (e.g., from typing import Optional)
• Wrong class name: Update import and instantiation to match actual class
• Missing docstring quotes: Add opening """ to docstring
• Wrong payload fields: Add missing required fields to payload dictionary
• Syntax errors: Fix unmatched quotes, parentheses, brackets

After Fixing:

• Read back the changed code to verify syntax
• Check the edit was correct (line numbers, indentation)
• Only fix ONE issue, even if multiple exist - don't cascade fixes
• Document what was changed in a clear comment

Example Fix:

# BEFORE
from typing import Dict, List, Any

# AFTER
from typing import Dict, List, Any, Optional

Phase 4: Restart (Automated)

Restart the backend server after each fix:

# Kill existing processes
lsof -ti:8000 | xargs kill -9 2>/dev/null

# Clear Python bytecode cache
find . -type d -name "__pycache__" -exec rm -rf {} + 2>/dev/null
find . -type f -name "*.pyc" -delete 2>/dev/null

# Restart backend
sleep 3 && python -m src.main --command web > /tmp/backend_restart.log 2>&1 &
sleep 10  # Wait for startup

# Verify health
curl -m 5 http://localhost:8000/api/health

Phase 5: Verification

Verify the fix worked through multiple checks:

Health Check:

• Call /api/health endpoint
• Verify "status": "healthy"
• If still failing, check logs for new errors

Browser Verification:

• Navigate to the affected UI page
• Trigger the action that previously failed
• Verify the error is gone
• Check for new errors in console

Database Verification:

• Query the affected records/tasks
• Verify status changed from failed/error to success/completed
• Check that metrics updated (e.g., scheduler shows "1 done" instead of "0 done")

Log Verification:

• Check recent logs for the same error
• Verify no new errors appeared
• Look for success messages or "completed" status

Example:

• Scheduler should show "1 done" instead of "0 done"
• Task record should show status="completed" instead of "failed"
• No error messages in logs
• WebSocket shows healthy status in UI

Phase 6: Iteration

If issues remain, repeat the cycle:

1. Continue if more issues exist:

   • Check logs for remaining errors
   • If yes, return to Phase 2 (Analysis)
   • Fix the next issue (Phase 3)
   • Restart (Phase 4)
   • Verify (Phase 5)

2. Stop when all issues fixed:

   • All schedulers show completed execution counts
   • UI shows no error states
   • Logs show no error patterns
   • Tasks/records show success status
   • Full verification complete

Common Error Patterns

See references/common_errors.md for patterns to recognize:

• Python syntax errors (unterminated strings, missing quotes)
• Import errors (name 'X' is not defined, cannot import name 'Y')
• Class/attribute errors ('dict' object has no attribute 'symbol')
• Type errors (passing wrong data type)
• Payload/configuration errors (missing required fields)

Fix Templates

See references/fix_templates.md for ready-to-use fix patterns:

• How to add missing imports
• How to fix class name mismatches
• How to fix docstring syntax
• How to add missing payload fields
• How to fix type errors

Tools Used

• Playwright Browser Tools: Navigate UI, verify changes
• Read/Grep Tools: Examine code and logs
• Bash: Server restart, cache clearing, health checks
• Edit Tool: Apply code fixes
• Database Queries: Verify task/record state

MCP Tools Integration

Use robo-trader-dev MCP tools for 95%+ token-efficient debugging:

Example debugging workflow:

# 1. Detect errors (MCP instead of tail/grep)
mcp__robo-trader-dev__analyze_logs(patterns=["ERROR", "TIMEOUT"], time_window="1h")

# 2. Check system health (MCP instead of curl loops)
mcp__robo-trader-dev__check_system_health(components=["database", "queues", "api_endpoints"])

# 3. Diagnose specific issue (MCP instead of sqlite3 + code reading)
mcp__robo-trader-dev__diagnose_database_locks(time_window="24h", include_code_references=True)

# 4. Get fix suggestions (MCP instead of manual pattern matching)
mcp__robo-trader-dev__suggest_fix(error_message="name 'Optional' is not defined", context_file="src/services/analyzer.py")

Integration with robo-trader architecture:

• Queue operations: Use queue_status to monitor PORTFOLIO_SYNC, DATA_FETCHER, AI_ANALYSIS
• Coordinator debugging: Use coordinator_status for BroadcastCoordinator, AIChatCoordinator init issues
• Database access: Use query_portfolio or diagnose_database_locks instead of direct sqlite3 connections

Key Principles

1. One issue at a time - Fix one problem per iteration to prevent cascading failures
2. Verify immediately - Always restart and verify after each fix
3. Multi-layer detection - Check UI, logs, and database for clues
4. Iterative refinement - Continue until all issues resolved
5. Automated restart - Always use clean restart (kill + cache clear + restart)
6. Browser verification - Always test in actual UI, not just logs