Codex-Claude-Cursor Engineering Loop Skill

Core Workflow Philosophy

This skill implements a 3-way sequential validation engineering loop:

• Claude Code: Architecture and planning, final review
• Codex: Plan validation (logic/security), code review (bugs/performance)
• Cursor Agent: Code implementation and execution
• Sequential Validation: Claude plans → Codex validates → Cursor implements → Codex reviews → Claude final check → repeat

Phase 1: Planning with Claude Code

1. Start by creating a detailed plan for the task
2. Break down the implementation into clear steps
3. Document assumptions and potential issues
4. Output the plan in a structured format

Phase 2: Plan Validation with Codex

1. Ask user (via AskUserQuestion):
   • Model: gpt-5 or gpt-5-codex
   • Reasoning effort: low, medium, or high
2. Send the plan to Codex for validation:

   echo "Review this implementation plan and identify any issues:
   [Claude's plan here]

   Check for:
   - Logic errors
   - Missing edge cases
   - Architecture flaws
   - Security concerns" | codex exec -m <model> --config model_reasoning_effort="<effort>" --sandbox read-only

3. Capture Codex's feedback and summarize to user

Phase 3: Plan Refinement Loop

If Codex finds issues in the plan:

1. Summarize Codex's concerns to the user
2. Refine the plan based on feedback
3. Ask user (via AskUserQuestion): "Should I revise the plan and re-validate, or proceed with implementation?"
4. Repeat Phase 2 if needed until plan is solid

Phase 4: Implementation with Cursor Agent

Once the plan is validated by Codex:

Session Management

1. Ask user (via AskUserQuestion): "Do you want to start a new Cursor session or resume an existing one?"

   • New session: Start fresh
   • Resume session: Continue previous work

2. If resuming:

   # List available sessions
   cursor-agent ls

   # Let user select session ID
   # Store session ID for subsequent calls

3. Ask user (via AskUserQuestion): Which Cursor model to use (e.g., composer-1, claude-3.5-sonnet, gpt-4o)

Implementation

4. Send the validated plan to Cursor Agent:

For new session:

   cursor-agent --model "<model-name>" -p --force "Implement this plan:
   [Validated plan here]

   Please implement the code following these specifications exactly."

For resumed session:

   cursor-agent --resume="<session-id>" -p --force "Continue implementation:
   [Validated plan here]"

5. IMPORTANT: Store the session ID from the output for all subsequent Cursor calls
6. Capture what was implemented and which files were modified

Phase 5: Codex Code Review

After Cursor implements:

1. Send Cursor's implementation to Codex for code review:

   echo "Review this implementation for:
   - Bugs and logic errors
   - Performance issues
   - Security vulnerabilities
   - Best practices violations
   - Code quality concerns

   Files modified: [list of files]
   Implementation summary: [what Cursor did]" | codex exec --sandbox read-only

2. Capture Codex's code review feedback
3. Summarize findings to user

Phase 6: Claude's Final Review

After Codex code review:

1. Claude reads the implemented code using Read tool
2. Claude analyzes both:
   • Codex's review findings
   • The actual implementation
3. Claude provides final assessment:
   • Verify if it matches the original plan
   • Confirm Codex's findings are valid
   • Identify any additional concerns
   • Make final architectural decisions
4. Summarize overall quality and readiness

Phase 7: Iterative Improvement Loop

If issues are found (by Codex or Claude):

1. Claude creates a detailed fix plan based on:
   • Codex's code review findings
   • Claude's final review insights
2. Send the fix plan to Cursor Agent using the same session:

   # IMPORTANT: Use --resume with the stored session ID
   cursor-agent --resume="<session-id>" -p --force "Fix these issues:
   [Detailed fix plan]

   Issues from Codex: [list]
   Issues from Claude: [list]"

3. After Cursor fixes, repeat from Phase 5 (Codex code review)
4. Continue the loop until all validations pass
5. Note:
   • Use same Codex model for consistency
   • Always use the same Cursor session ID to maintain context
   • Session maintains full history of changes

Recovery When Issues Are Found

When Codex finds plan issues (Phase 2):

1. Claude analyzes Codex's concerns
2. Refines the plan addressing all issues
3. Re-submits to Codex for validation
4. Repeats until Codex approves

When Codex finds code issues (Phase 5):

1. Claude reviews Codex's findings
2. Creates detailed fix plan
3. Sends to Cursor for fixes
4. After Cursor fixes, back to Codex review
5. Repeats until Codex approves

When Claude finds issues (Phase 6):

1. Claude creates comprehensive fix plan
2. Sends to Cursor for implementation
3. After fixes, Codex reviews again
4. Claude does final check
5. Repeats until Claude approves

Best Practices

• Always validate plans with Codex before implementation
• Never skip Codex code review after Cursor implements
• Never skip Claude's final review for architectural oversight
• Maintain clear handoff between all three AIs
• Document who did what for context
• Use same models throughout (same Codex model, same Cursor model)
• Session Management:
  • Always use --resume with same session ID for iterative fixes
  • Store session ID at the start and reuse throughout
  • Use cursor-agent ls to find previous sessions
  • Only start new session when beginning completely new feature

Command Reference

Error Handling

1. Monitor Cursor Agent output for errors
2. Summarize Cursor's implementation results and Claude's review
3. Ask for user direction via AskUserQuestion if:
   • Significant architectural changes needed
   • Multiple files will be affected
   • Breaking changes are required
4. When issues appear, Claude creates a detailed fix plan before sending to Cursor

The Perfect Loop

1. Plan (Claude)
   ↓
2. Validate Plan (Codex) → if issues → refine plan → repeat
   ↓
3. Implement (Cursor)
   ↓
4. Code Review (Codex) → captures bugs/performance issues
   ↓
5. Final Review (Claude) → architectural check
   ↓
6. Issues found? → Fix Plan (Claude) → Implement Fixes (Cursor) → back to step 4
   ↓
7. All passed? → Done! ✅

This creates a triple-validation, self-correcting, high-quality engineering system where:

• Claude: All planning, architecture, and final oversight
• Codex: All validation (plan logic + code quality)
• Cursor Agent: All implementation and coding