Planning

Implementation Planning Skill

✨ SKILL ACTIVATED: planning
   Purpose: Strategic implementation planning methodology
   Functionality: Requirements clarification, strategy design, change specification, risk mitigation
   Output: Detailed, step-by-step execution plans with validation strategies
   Scope: Portable across VS Code, CLI, Claude, Cursor, and compatible agents

Purpose

Transforms requirements and repository analysis into actionable, step-by-step implementation plans with comprehensive risk mitigation, validation strategies, and quality gates. Bridges analysis and execution phases.

When to Use This Skill

• Planning new feature implementation
• Designing refactoring strategies
• Creating migration plans
• Organizing complex code changes
• Preparing for code reviews
• Establishing validation approaches

Planning Framework

Phase 1: Requirements Clarification

Objective: Ensure complete understanding of what needs to be built

Clarification Questions:

Functional Requirements:
  - What should the feature/change do?
  - What are the acceptance criteria?
  - What are the edge cases?
  - What are the performance requirements?

Technical Constraints:
  - Are there API compatibility requirements?
  - What are the backward compatibility needs?
  - Are there security considerations?
  - What are the testing requirements?

Context:
  - Why is this change needed?
  - What problem does it solve?
  - Who are the users/consumers?
  - What's the priority/urgency?

Output: Clear, documented requirements with acceptance criteria

Phase 2: Strategy Design

Objective: Define high-level approach to implementation

Strategy Options:

1. Incremental Approach

   • Break into small, testable changes
   • Each step is independently valuable
   • Minimize risk through gradual rollout
   • Best for: Large features, refactoring

2. Big Bang Approach

   • Complete implementation in one go
   • All changes deployed together
   • Faster delivery but higher risk
   • Best for: Small features, tight coupling

3. Parallel Development

   • Build new alongside old
   • Switch over when ready
   • Zero downtime migration
   • Best for: Infrastructure changes, replacements

4. Feature Flag Approach

   • Implement behind toggle
   • Gradual rollout control
   • Easy rollback mechanism
   • Best for: High-risk features, A/B testing

Decision Matrix:

Output: Selected strategy with justification

Orchestration Assessment: When the implementation plan involves 3+ specialized agents:

• Assess whether a conductor/subagent pattern would improve coordination
• Lightweight conductor: 3 agents, sequential coordination, basic quality gates
• Orchestra pattern: 4-5 agents, TDD lifecycle, full quality gate framework
• Atlas pattern: 6-10 agents, parallel execution, context conservation
• Include orchestration specification in the plan output (do not defer to separate workflow)
• See orchestration skill for complete methodology

Phase 3: Change Specification

Objective: Detail every file and change required

File-by-File Breakdown:

### File: src/services/userService.ts
**Action**: MODIFY
**Changes**:
  - Add new method: getUserPreferences()
  - Update existing: updateUser() to handle preferences
  - Add validation: preferenceSchema

**Affected Lines**: Approx 45-67, new function at end

**Dependencies**:
  - Imports PreferenceType from types/preferences.ts
  - Uses PreferenceRepository (new)

**Risk**: LOW (isolated change, existing tests cover)

---

### File: src/types/preferences.ts
**Action**: CREATE
**Content**:
  - Export PreferenceType interface
  - Export PreferenceCategory enum
  - Export validation schemas

**Template**: [See example below]

**Dependencies**: None (new isolated file)

**Risk**: LOW (new file, no breaking changes)

---

### File: tests/userService.test.ts
**Action**: MODIFY
**Changes**:
  - Add test suite: getUserPreferences()
  - Update test: updateUser() with preferences

**Test Cases**:
  - Valid preferences retrieval
  - Invalid user ID handling
  - Preference update flow
  - Edge case: empty preferences

**Risk**: LOW (test file, no production impact)

Output: Complete file change specification

Phase 4: Dependency Management

Objective: Plan for new dependencies and version changes

New Dependencies:

packages:
  - name: zod
    version: ^3.22
    purpose: Runtime validation for preferences
    justification: Type-safe validation, widely used
    alternatives: yup, joi (heavier, less TS-friendly)
    risk: LOW (stable, well-maintained)

  - name: lodash.merge
    version: ^4.6
    purpose: Deep merge for preference updates
    justification: Battle-tested, specific import reduces bundle
    alternatives: Native spread (doesn't handle deep merge)
    risk: LOW (micro-package, stable)

Version Updates (if needed):

• Current package vulnerabilities to fix
• Breaking changes to handle
• Migration steps required

Output: Dependency change plan with risk assessment

Phase 5: Testing Strategy

Objective: Define comprehensive test approach

Test Levels:

1. Unit Tests

   Target:
     - New functions: getUserPreferences(), updateUser()
     - New validation: preferenceSchema
   
   Coverage:
     - Happy path (valid inputs)
     - Edge cases (empty, null, undefined)
     - Error cases (invalid types, DB failures)
   
   Approach:
     - Mock external dependencies (DB, services)
     - Test isolation (one function per suite)
     - Clear assertions (exact expected values)
   

2. Integration Tests

   Target:
     - End-to-end preference flow
     - Database interaction
     - API endpoint behavior
   
   Scenarios:
     - Create user with preferences
     - Update preferences
     - Retrieve preferences
     - Delete user (cascade to preferences)
   

3. Performance Tests (if needed)

   Target:
     - Query performance with large datasets
     - Concurrent update handling
   
   Benchmarks:
     - Response time <200ms for preference retrieval
     - Handle 100 concurrent updates
   

Test-First Approach (TDD):

1. Write failing test for getUserPreferences()
2. Implement minimal code to pass
3. Refactor for quality
4. Repeat for each function

Output: Test plan with specific test cases

Phase 6: Risk Mitigation

Objective: Identify and plan for potential issues

Risk Catalog:

Risk: Breaking existing user update functionality
  Likelihood: MEDIUM
  Impact: HIGH
  Mitigation:
    - Comprehensive test coverage of existing behavior
    - Feature flag for preference handling
    - Backward compatible API (optional preferences field)
  Rollback:
    - Toggle feature flag off
    - Redeploy previous version if needed

Risk: Database migration failure in production
  Likelihood: LOW
  Impact: HIGH
  Mitigation:
    - Test migration on production-like data
    - Backup database before migration
    - Reversible migration script
  Rollback:
    - Run down migration script
    - Restore from backup if needed

Risk: Performance degradation on preference queries
  Likelihood: LOW
  Impact: MEDIUM
  Mitigation:
    - Add database index on user_id + preference_key
    - Load test with realistic data volume
    - Query optimization review
  Rollback:
    - Remove index if causing issues
    - Cache preference queries

Risk Matrix:

Output: Risk register with mitigation strategies

Phase 7: Validation Planning

Objective: Define how success will be measured

Validation Levels:

1. Code Quality Validation

   Automated:
     - Linter passes (no warnings)
     - Type checking passes (strict mode)
     - Unit tests pass (100% of new code)
     - Integration tests pass
   
   Manual:
     - Code review approval (2+ reviewers)
     - Security review (if touching auth/data)
     - Architecture review (if major changes)
   

2. Functional Validation

   Acceptance Criteria:
     ✓ Users can set preferences
     ✓ Preferences persist across sessions
     ✓ Invalid preferences are rejected
     ✓ Preference updates are atomic
   
   Test Cases:
     ✓ Happy path works end-to-end
     ✓ Edge cases handled correctly
     ✓ Error messages are clear
   

3. Performance Validation

   Benchmarks:
     - P50 latency: <100ms (preference retrieval)
     - P99 latency: <500ms
     - Throughput: >1000 req/sec
   
   Load Testing:
     - 100 concurrent users
     - 10,000 preferences in database
     - No memory leaks over 1 hour
   

4. Production Validation

   Monitoring:
     - Error rate <0.1%
     - Response time within SLA
     - No database deadlocks
     - Memory usage stable
   
   Rollout:
     - Canary: 5% of traffic for 1 hour
     - Gradual: 50% for 24 hours
     - Full: 100% after validation
   

Output: Validation checklist with success metrics

Phase 8: Implementation Sequence

Objective: Order changes for minimal disruption

Sequencing Strategy:

Phase 1: Foundation (No user impact)
  1. Create new types (preferences.ts)
  2. Add database schema/migration
  3. Create preference repository
  4. Write unit tests for repository

Phase 2: Integration (Still no user impact)
  5. Add preference methods to userService
  6. Write unit tests for service methods
  7. Update API endpoints (feature flagged OFF)
  8. Write integration tests

Phase 3: Activation (Gradual rollout)
  9. Enable feature flag for internal users
  10. Monitor for 24 hours
  11. Gradual rollout to production
  12. Remove feature flag after stabilization

Dependency Order:

types/preferences.ts (no dependencies)
  ↓
repositories/preferenceRepository.ts (depends on types)
  ↓
services/userService.ts (depends on repository)
  ↓
api/userController.ts (depends on service)
  ↓
tests/* (depends on implementations)

Output: Ordered task list with dependencies

Implementation Plan Template

# Implementation Plan: [Feature Name]

## Overview
**Objective**: [Clear goal statement]
**Strategy**: [Chosen approach]
**Risk Level**: [LOW/MEDIUM/HIGH]
**Estimated Effort**: [Hours/days]

## Requirements
**Functional**:
- [Requirement 1]
- [Requirement 2]

**Non-Functional**:
- Performance: [Criteria]
- Security: [Requirements]
- Compatibility: [Constraints]

**Acceptance Criteria**:
- [ ] [Criterion 1]
- [ ] [Criterion 2]

## Implementation Strategy
**Approach**: [Incremental/Big Bang/Parallel/Feature Flag]
**Justification**: [Why this approach]

**Phases**:
1. [Phase name]: [Description]
2. [Phase name]: [Description]

## File Changes

### New Files
| File | Purpose | Risk | Dependencies |
|------|---------|------|--------------|
| [path] | [purpose] | [LOW/MED/HIGH] | [list] |

### Modified Files
| File | Changes | Risk | Impact |
|------|---------|------|--------|
| [path] | [summary] | [LOW/MED/HIGH] | [description] |

### Deleted Files
| File | Reason | Risk | Migration |
|------|--------|------|-----------|
| [path] | [why] | [LOW/MED/HIGH] | [how] |

## Dependencies
**New Packages**:
- [package@version]: [purpose]

**Updates**:
- [package]: [old] → [new] (reason)

## Testing Plan
**Unit Tests**:
- [ ] [Test suite 1]
- [ ] [Test suite 2]

**Integration Tests**:
- [ ] [Test scenario 1]
- [ ] [Test scenario 2]

**Performance Tests**:
- [ ] [Benchmark 1]

## Risk Mitigation
| Risk | Likelihood | Impact | Mitigation |
|------|-----------|--------|------------|
| [risk] | [L/M/H] | [L/M/H] | [strategy] |

## Validation Checklist
- [ ] Code quality (linter, types, tests)
- [ ] Functional (acceptance criteria met)
- [ ] Performance (benchmarks met)
- [ ] Security (review complete)
- [ ] Production (monitoring configured)

## Implementation Sequence
1. [ ] **Foundation**: [Tasks]
2. [ ] **Integration**: [Tasks]
3. [ ] **Activation**: [Tasks]

## Rollback Plan
**Triggers**:
- [Condition that requires rollback]

**Steps**:
1. [Rollback action]
2. [Verification step]

## Success Metrics
- [Metric 1]: [Target]
- [Metric 2]: [Target]

---
**Approval Required**: ✋ User confirmation before execution
**Next Step**: Hand off to Editor agent (VS Code)

Quality Gates

Before Starting Implementation

• Requirements fully understood
• All stakeholders aligned
• Technical approach validated
• Risks identified and mitigated
• User approval obtained ✋

During Implementation

• Following plan sequence
• Tests passing incrementally
• Code review feedback addressed
• Documentation updated

Before Production

• All acceptance criteria met
• Performance benchmarks validated
• Security review complete
• Rollback plan tested

Best Practices

Clarity

• Use specific file paths and line numbers
• Provide code examples where helpful
• Link to relevant documentation

Risk Awareness

• Be realistic about risks (don't sugarcoat)
• Provide concrete mitigation strategies
• Always have a rollback plan

User Communication

• Present plan clearly for approval
• Highlight high-risk areas
• Provide effort estimates
• Set expectations on timeline

Flexibility

• Build in checkpoints for reassessment
• Allow for plan adjustments
• Don't over-specify (leave room for implementation decisions)

Integration with Other Skills

Works well with:

• repo-analysis — Analyze codebase before creating implementation strategy
• asset-design — Plan deployment of designed customization assets
• orchestration — Create phased plans for orchestrated system implementation
• documentation — Document implementation approach and decisions

Typical workflow: repo-analysis identifies scope → this skill creates implementation plan → user approves → execution proceeds → documentation captures outcomes

Workflow Example:

repo-analysis (understand context)
  ↓
planning (create strategy) ← THIS SKILL
  ↓
[USER APPROVAL GATE] ✋
  ↓
VS Code Editor (execute plan)
  ↓
VS Code Verifier (validate)

Success Criteria

A good implementation plan provides:

• ✅ Clear, actionable steps
• ✅ Comprehensive risk assessment
• ✅ Detailed test strategy
• ✅ Realistic effort estimates
• ✅ Concrete validation criteria
• ✅ Rollback procedures

Skill Type: Planning and Strategy
Complexity: Medium-High
Typical Duration: 10-30 minutes
Prerequisites: Requirements clarity, repository analysis

Cross-Platform: Works in VS Code, GitHub Copilot CLI, Claude, Cursor, and other Skills-compatible agents.

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