Implementation Plan Creation

Create an implementation plan in docs/plans/yyyymmdd-<task-name>.md with interactive context gathering.

Step 0: Parse Intent and Gather Context

Before asking questions, understand what the user is working on:

1. Parse user’s command arguments to identify intent:

   • “add feature Z” / “implement W” → feature development
   • “fix bug” / “debug issue” → bug fix plan
   • “refactor X” / “improve Y” → refactoring plan
   • “migrate to Z” / “upgrade W” → migration plan
   • generic request → explore current work

2. Launch Explore agent (via Task tool with subagent_type: Explore) to gather relevant context based on intent:

   For feature development:

   • locate related existing code and patterns
   • check project structure (README, config files, existing similar implementations)
   • identify affected components and dependencies

   For bug fixing:

   • look for error logs, test failures, or stack traces
   • find related code that might be involved
   • check recent git changes in problem areas

   For refactoring/migration:

   • identify all files/components affected
   • check test coverage of affected areas
   • find dependencies and integration points

   For generic/unclear requests:

   • check git status and recent file activity
   • examine current working directory structure
   • identify primary language/framework from file extensions and config files

3. Synthesize findings into context summary:

   • what work is in progress
   • which files/areas are involved
   • what the apparent goal is
   • relevant patterns or structure discovered

Step 1: Present Context and Ask Focused Questions

Show the discovered context, then ask questions one at a time using the AskUserQuestion tool:

“Based on your request, I found: [context summary]”

Ask questions one at a time (do not overwhelm with multiple questions):

1. Plan purpose: use AskUserQuestion – “What is the main goal?”

   • provide multiple choice with suggested answer based on discovered intent
   • wait for response before next question

2. Scope: use AskUserQuestion – “Which components/files are involved?”

   • provide multiple choice with suggested discovered files/areas
   • wait for response before next question

3. Constraints: use AskUserQuestion – “Any specific requirements or limitations?”

   • can be open-ended if constraints vary widely
   • wait for response before next question

4. Testing approach: use AskUserQuestion – “Do you prefer TDD or regular approach?”

   • options: “TDD (tests first)” and “Regular (code first, then tests)”
   • store preference for reference during implementation
   • wait for response before next question

5. Plan title: use AskUserQuestion – “Short descriptive title?”

   • provide suggested name based on intent

After all questions answered, synthesize responses into plan context.

Step 1.5: Explore Approaches

Once the problem is understood, propose implementation approaches:

1. Propose 2-3 different approaches with trade-offs for each
2. Lead with recommended option and explain reasoning
3. Present conversationally – not a formal document yet

Example format:

I see three approaches:

**Option A: [name]** (recommended)
- How it works: ...
- Pros: ...
- Cons: ...

**Option B: [name]**
- How it works: ...
- Pros: ...
- Cons: ...

Which direction appeals to you?

Use AskUserQuestion tool to let user select preferred approach before creating the plan.

Skip this step if:

• the implementation approach is obvious (single clear path)
• user explicitly specified how they want it done
• it’s a bug fix with clear solution

Step 2: Create Plan File

Check docs/plans/ for existing files, then create docs/plans/<task-name>.md:

Plan Structure

# [Plan Title]

## Overview
- Clear description of the feature/change being implemented
- Problem it solves and key benefits
- How it integrates with existing system

## Context (from discovery)
- Files/components involved: [list from step 0]
- Related patterns found: [patterns discovered]
- Dependencies identified: [dependencies]

## Development Approach
- **Testing approach**: [TDD / Regular - from user preference in planning]
- Complete each task fully before moving to the next
- Make small, focused changes
- **CRITICAL: every task MUST include new/updated tests** for code changes in that task
  - tests are not optional - they are a required part of the checklist
  - write unit tests for new functions/methods
  - write unit tests for modified functions/methods
  - add new test cases for new code paths
  - update existing test cases if behavior changes
  - tests cover both success and error scenarios
- **CRITICAL: all tests must pass before starting next task** - no exceptions
- **CRITICAL: update this plan file when scope changes during implementation**
- Run tests after each change
- Maintain backward compatibility

## Testing Strategy
- **Unit tests**: required for every task (see Development Approach above)
- **E2E tests**: if project has UI-based e2e tests (Playwright, Cypress, etc.):
  - UI changes → add/update e2e tests in same task as UI code
  - Backend changes supporting UI → add/update e2e tests in same task
  - Treat e2e tests with same rigor as unit tests (must pass before next task)
  - Store e2e tests alongside unit tests (or in designated e2e directory)

## Progress Tracking
- Mark completed items with `[x]` immediately when done
- Add newly discovered tasks with ➕ prefix
- Document issues/blockers with ⚠️ prefix
- Update plan if implementation deviates from original scope
- Keep plan in sync with actual work done

## What Goes Where
- **Implementation Steps** (`[ ]` checkboxes): tasks achievable within this codebase - code changes, tests, documentation updates
- **Post-Completion** (no checkboxes): items requiring external action - manual testing, changes in consuming projects, deployment configs, third-party verifications

## Implementation Steps

<!--
Task structure guidelines:
- Each task = ONE logical unit (one function, one endpoint, one component)
- Use specific descriptive names, not generic "[Core Logic]" or "[Implementation]"
- Aim for ~5 checkboxes per task (more is OK if logically atomic)
- **CRITICAL: Each task MUST end with writing/updating tests before moving to next**
  - tests are not optional - they are a required deliverable of every task
  - write tests for all NEW code added in this task
  - write tests for all MODIFIED code in this task
  - include both success and error scenarios in tests
  - list tests as SEPARATE checklist items, not bundled with implementation

Example (NOTICE: tests are separate checklist items):

### Task 1: Add password hashing utility
- [ ] create `auth/hash` module with HashPassword and VerifyPassword functions
- [ ] implement secure hashing with configurable cost
- [ ] write tests for HashPassword (success + error cases)
- [ ] write tests for VerifyPassword (success + error cases)
- [ ] run project tests - must pass before task 2

### Task 2: Add user registration endpoint
- [ ] create `POST /api/users` handler
- [ ] add input validation (email format, password strength)
- [ ] integrate with password hashing utility
- [ ] write tests for handler success case with table-driven cases
- [ ] write tests for handler error cases (invalid input, missing fields)
- [ ] run project tests - must pass before task 3
-->

### Task 1: [specific name - what this task accomplishes]
- [ ] [specific action with file reference - code implementation]
- [ ] [specific action with file reference - code implementation]
- [ ] write tests for new/changed functionality (success cases)
- [ ] write tests for error/edge cases
- [ ] run tests - must pass before next task

### Task N-1: Verify acceptance criteria
- [ ] verify all requirements from Overview are implemented
- [ ] verify edge cases are handled
- [ ] run full test suite (unit tests)
- [ ] run e2e tests if project has them
- [ ] run linter - all issues must be fixed
- [ ] verify test coverage meets project standard (80%+)

### Task N: [Final] Update documentation
- [ ] update README.md if needed
- [ ] update project knowledge docs if new patterns discovered

## Technical Details
- Data structures and changes
- Parameters and formats
- Processing flow

## Post-Completion
*Items requiring manual intervention or external systems - no checkboxes, informational only*

**Manual verification** (if applicable):
- Manual UI/UX testing scenarios
- Performance testing under load
- Security review considerations

**External system updates** (if applicable):
- Consuming projects that need updates after this library change
- Configuration changes in deployment systems
- Third-party service integrations to verify

Step 3: Offer to Start

After creating the file, tell user:

“Created plan: docs/plans/<task-name>.md

Ready to start implementation?”

If yes, begin with task 1.

Execution Enforcement

CRITICAL testing rules during implementation:

1. After completing code changes in a task:

   • STOP before moving to next task
   • Add tests for all new functionality
   • Update tests for modified functionality
   • Run project test command
   • Mark completed items with [x] in plan file
   • Use TodoWrite tool to track progress and mark todos completed immediately (do not batch)

2. If tests fail:

   • Fix the failures before proceeding
   • Do NOT move to next task with failing tests
   • Do NOT skip test writing

3. Only proceed to next task when:

   • All task items completed and marked [x]
   • Tests written/updated
   • All tests passing

4. Plan tracking during implementation:

   • Update checkboxes immediately when tasks complete
   • Add ➕ prefix for newly discovered tasks
   • Add ⚠️ prefix for blockers
   • Modify plan if scope changes significantly

5. On completion:

   • Verify all checkboxes marked
   • Run final test suite

6. Partial implementation exception:

   • If a task provides partial implementation where tests cannot pass until a later task:
     • Still write the tests as part of this task (required)
     • Add TODO comment in test code noting the dependency
     • Mark the test checkbox as completed with note: [x] write tests ... (fails until Task X)
     • Do NOT skip test writing or defer until later
   • When the dependent task completes, remove the TODO comment and verify tests pass

This ensures each task is solid before building on top of it.

Key Principles

• One question at a time – do not overwhelm user with multiple questions in a single message
• Multiple choice preferred – easier to answer than open-ended when possible
• YAGNI ruthlessly – remove unnecessary features from all designs, keep scope minimal
• Lead with recommendation – have an opinion, explain why, but let user decide
• Explore alternatives – always propose 2-3 approaches before settling (unless obvious)
• Duplication vs abstraction – when code repeats, ask user: prefer duplication (simpler, no coupling) or abstraction (DRY but adds complexity)? explain trade-offs before deciding