Implement

Implements specifications using TDD methodology: Phase X.0 (tests first), Phase X.1 (implementation), Phase X.2 (review).

When to Use This Skill

• •Implementing a spec after spec has been created
• •Following TDD workflow
• •Executing Phase X.0 (test foundation)
• •Executing Phase X.1 (implementation)
• •Phase X.2 (quality review before merge)

Workflow Overview

Read spec.md + checklist.md + spec-research.md
    │
    ▼
Phase X.0: Test Foundation (all FRs)
    │
    ├─ Write failing tests for each FR
    ├─ Commit with test(FR{N}) prefix
    ├─ GATE: red-phase-test-validator (must PASS)
    │
    ▼
Phase X.1: Implementation (all FRs)
    │
    ├─ Implement to make tests pass
    ├─ Commit with feat(FR{N}) prefix
    │
    ▼
Phase X.2: Review (all 4 steps mandatory)
    │
    ├─ Step 0: spec-implementation-alignment (must PASS)
    ├─ Step 1: pr-review-toolkit:review-pr (6 agents)
    ├─ Step 2: Address feedback, fix issues
    ├─ Step 3: test-optimiser (final pass)
    │
    ▼
Implementation complete

Critical Stop Guidance (Andon)

During implementation, if you encounter a disconnect that breaks fundamental spec assumptions, stop and escalate.

Stop Conditions

• •Interface contract requires data that doesn't exist and can't be derived
• •Spec assumes dependency/provider that doesn't exist
• •Core data flow is impossible as designed

When Triggered

Do NOT work around silently. Escalate:

IMPLEMENTATION BLOCKED

Spec assumes: [quote the specific requirement]
Reality: [what actually exists or doesn't]

This breaks: [interface contract / data flow / core assumption]

Options:
1. Return to Spec/Research to address
2. Descope this requirement
3. [Other options if apparent]

Need decision to proceed.

What IS Critical (Stop)

What's NOT Critical (Proceed with Note)

The Test

Does this break the interface contracts or fundamental assumptions?

• •Yes → STOP and escalate
• •No → Note issue, proceed

After Escalation

Based on user decision:

• •Resume: Workaround approved, continue with modified approach
• •Return: Go back to Spec/Research to fix the gap properly
• •Descope: Remove the blocked requirement, continue with reduced scope

Stage 1: Load Context

Read Spec Artifacts

1. •Read spec.md for requirements (FRs with success criteria)
2. •Read checklist.md for task list
3. •Read spec-research.md for implementation context

Using Research Context

The spec-research.md contains:

• •Interface Contracts - Types and function signatures
• •Key Decisions - Rationale for approach
• •Test Plan - Test cases derived from contracts

Use these as the source of truth for implementation.

Stage 1.5: FR Dependency Analysis (for Parallel Execution)

When running as spec-executor (orchestrating sub-agents), analyze FR dependencies before execution.

Identify FR Dependencies

Read spec-research.md Test Plan section. For each FR, determine:

• •Does this FR's implementation depend on types/functions from another FR?
• •Does this FR's test require mocks that another FR provides?

Build FR Dependency Graph

Execution Waves

Group FRs into waves based on dependencies:

Wave 1: FRs with no dependencies (FR1, FR3) Wave 2: FRs depending only on Wave 1 (FR2) Wave 3: FRs depending on Wave 2 (...)

This wave structure drives parallel sub-agent dispatch.

Stage 2: Determine Phase

Check checklist.md status:

• •If Phase X.0 tasks incomplete OR Test Design Validation incomplete: Start/continue Phase X.0
• •If Phase X.0 + validation complete, Phase X.1 incomplete: Start/continue Phase X.1
• •If Phase X.1 complete, Phase X.2 incomplete: Run Phase X.2 Review
• •If all complete: Confirm completion with user

Phase X.0: Test Foundation

Goal: Write failing tests that verify each Functional Requirement.

For Each FR in spec.md:

1. •Identify test cases from Success Criteria
2. •Write test file (or add to existing)
3. •Run tests to verify they fail appropriately
4. •Update checklist marking test tasks complete

Test Guidelines:

• •One test file per component/module when practical
• •Test names should reference FR: test_FR1_accepts_valid_input
• •Focus on behavior, not implementation
• •Include edge cases from spec

Parallel Execution (Spec-Executor Mode)

When orchestrating via spec-executor, dispatch FR test work in parallel:

Wave-Based Dispatch:

1. •

   Wave 1 - Launch parallel sub-agents for independent FRs:

   code

   Task(subagent_type="general-purpose",
        description="FR1 tests",
        prompt="Write tests for FR1 per spec. File: {test-file}")
   
   Task(subagent_type="general-purpose",
        description="FR3 tests",
        prompt="Write tests for FR3 per spec. File: {test-file}")
   

2. •

   Wait for Wave 1 completion

3. •

   Wave 2 - Launch sub-agents for newly unblocked FRs:

   code

   Task(subagent_type="general-purpose",
        description="FR2 tests",
        prompt="Write tests for FR2 per spec. FR1 types now available.")
   

4. •

   Continue until all FR tests complete

5. •

   Run red-phase-test-validator on combined test output

Commits (Phase X.0):

One commit per FR test group. Use the standard commit format (see Commit Discipline section):

git add {test-file-path}
git commit -m "test(FR1): add input validation tests ..."  # HEREDOC format with Co-Author-By

Stage only test files, not implementation files.

Phase X.0 Completion:

Verify:

• • All FRs have corresponding tests
• • All tests fail (red phase)
• • Test checklist items marked complete
• • GATE: red-phase-test-validator returns PASS (see below)

GATE: Test Design Validation

⚠️ Do NOT proceed to Phase X.1 until this gate passes.

Run the red-phase-test-validator agent:

subagent_type: "red-phase-test-validator"
description: "Validate test design quality"
prompt: "Validate the tests written for this spec:

Test files: {paths to test files}
Spec: {spec-path}/spec.md
Research: {spec-path}/spec-research.md

Check:
1. Spec alignment - all FR success criteria have tests
2. Assertion specificity - tests verify specific behavior
3. Mock discipline - mocks at boundaries, realistic data
4. Behavior focus - tests describe WHAT, not HOW

Report PASS or FAIL with specific issues."

If PASS: Proceed to Phase X.1

If FAIL:

1. •Review specific issues (missing coverage, weak assertions, over-mocking)
2. •Fix test design issues
3. •Re-run validation
4. •Repeat until PASS (max 2 iterations)

Why this matters: Weak tests lead to implementation guided by weak contracts. Tests failing ≠ tests well-designed. This gate catches no-op tests, missing coverage, and poor mock discipline before you implement against them.

Phase X.1: Implementation

Goal: Implement code to make tests pass.

For Each Failing Test:

1. •Read test to understand expected behavior
2. •Implement minimum code to pass the test
3. •Run test to verify it passes
4. •Refactor if needed (tests should still pass)
5. •Update checklist marking impl tasks complete

Implementation Guidelines:

• •Follow patterns from spec-research.md
• •Reference files listed in Technical Design
• •Keep changes minimal and focused
• •Target 50-150 lines per FR (200 max)

Parallel Execution (Spec-Executor Mode)

Same wave-based pattern as Phase X.0:

1. •Dispatch Wave 1 implementation sub-agents in parallel
2. •Wait for completion
3. •Dispatch Wave 2 (now unblocked)
4. •Continue until all FRs implemented
5. •Run full test suite to verify integration

Commits (Phase X.1):

One commit per FR implementation. Use the standard commit format (see Commit Discipline section):

git add {implementation-file-path}
git commit -m "feat(FR1): implement validation logic ..."  # HEREDOC format with Co-Author-By

Stage only implementation files, NOT test files (they were committed in X.0).

Phase X.1 Completion:

Verify:

• • All tests pass (green phase)
• • All implementation checklist items complete
• • No regressions in existing tests

Next: Phase X.2 is MANDATORY. Do not commit or skip to completion.

Phase X.2: Review

⚠️ MANDATORY GATE - Do NOT commit until this phase is complete.

Goal: Quality gate before PR. Catch issues that would be found in human review.

Always run all four steps. No scope-based shortcuts - every change gets full QC.

Step 0: Spec-Implementation Alignment

Run this FIRST. No point reviewing code quality if it's the wrong code.

Run the spec-implementation-alignment agent:

subagent_type: "spec-implementation-alignment"
description: "Verify implementation matches spec"
prompt: "Validate implementation alignment:
- spec.md: {spec-path}/spec.md
- spec-research.md: {spec-path}/spec-research.md
- checklist.md: {spec-path}/checklist.md

Verify:
1. Each FR success criterion is satisfied by the implementation
2. Types/signatures match interface contracts
3. No scope creep (features added beyond spec)
4. No scope shortfall (requirements quietly dropped)

Report PASS or FAIL with specific gaps."

If PASS: Proceed to Step 1 (code quality)

If FAIL:

1. •Review specific gaps
2. •Fix alignment issues (or escalate if spec needs updating)
3. •Re-run alignment check
4. •Repeat until PASS (max 2 iterations)

If stuck: Escalate to user - may need spec revision.

Step 1: Comprehensive PR Review

Run the pr-review-toolkit:review-pr skill for multi-agent analysis:

Use Skill tool:
skill: "pr-review-toolkit:review-pr"

This runs 6 specialized agents:

Step 2: Address Feedback

If issues found:

1. •Review each agent's findings
2. •Fix issues by priority (critical → high → medium)
3. •Re-run tests to ensure fixes don't break anything
4. •Commit fixes: fix({spec}): {description}

If no significant issues:

• •Proceed to Step 3

Step 3: Test Quality Optimization

Run the test-optimiser agent as a final pass:

subagent_type: "test-optimiser"
description: "Optimize test quality"
prompt: "Review the tests for this spec implementation.

Focus on recently modified test files. Ensure tests provide genuine confidence:
- Tests would fail if implementation were broken
- Behavior tested, not implementation details
- Edge cases and error paths covered
- No pageantry testing (tests that look good but verify nothing)

Optimize any weak tests found."

Handle Final Results

If test-optimiser suggests changes:

1. •Review suggested improvements
2. •Apply changes that strengthen test confidence
3. •Re-run tests
4. •Commit: fix({spec}): strengthen test assertions

If all passes:

1. •Confirm: "Review passed. Implementation complete."

Stage 3: Completion

After review complete, update documentation and finalize.

3.1: Verify Checklist Complete

Read {spec-path}/checklist.md and verify all tasks marked [x]:

• • All Phase X.0 tasks complete
• • All Phase X.1 tasks complete
• • All Phase X.2 tasks complete

If any tasks unmarked, update them now.

3.2: Add Session Notes

Append to checklist.md:

## Session Notes

**{date}**: Implementation complete.
- Phase X.0: {N} test commits
- Phase X.1: {N} implementation commits
- Phase X.2: Review passed, {N} fix commits (if any)
- All tests passing.

3.3: Update FEATURE.md

Read features/{domain}/{feature}/FEATURE.md and update:

1. •

   Changelog section - Update spec entry:

   markdown

   ### {NN}-{spec-name}
   - **Status**: Complete
   - **Date**: {date}
   - **Commits**: test(FR1-N), feat(FR1-N), fix (if any)
   

2. •

   Files Touched section - Add any new files created

3.4: Commit Documentation Updates

git add {spec-path}/checklist.md features/{domain}/{feature}/FEATURE.md
git commit -m "$(cat <<'EOF'
docs({NN}-{spec-name}): update checklist and FEATURE.md

- Mark all checklist tasks complete
- Add session notes
- Update FEATURE.md changelog

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
EOF
)"
git status  # Verify clean working tree

3.5: Confirm with User

"Implementation complete for {NN}-{spec-name}.

Commits (in TDD order):
1. test(FR1-N): tests for all FRs
2. feat(FR1-N): implementations for all FRs
3. fix({spec}): review fixes (if any)
4. docs({spec}): documentation updates

Documentation Updated:
  ✓ checklist.md - all tasks marked complete, session notes added
  ✓ FEATURE.md - changelog updated

All tests passing. Git state clean.

Next step: Proceed to next spec using `spec` then `implement` skills"

Checklist Management

Use Edit tool to update checklist.md as you work:

# Before
- [ ] Task description

# After
- [x] Task description

Add session notes at bottom:

## Session Notes

**2025-01-05**: Completed X.0 and X.1. Review found 2 issues, both fixed.

Commit Discipline

Each spec follows this commit sequence:

Note: The spec() commit is created by the spec skill before implement runs.

Commit Format (REQUIRED)

Always use HEREDOC format with Co-Author-By:

git add {specific-files}  # Never use git add -A
git commit -m "$(cat <<'EOF'
{prefix}({scope}): {concise description}

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
EOF
)"
git status  # Verify commit succeeded

Anti-Patterns

• •NEVER bundle tests and implementation in one commit
• •NEVER use git add -A or git add . - stage specific files
• •NEVER skip git status verification after commit
• •NEVER commit implementation before tests (breaks TDD visibility)

Key Principles

• •Tests Before Implementation: Always write tests before code
• •Small Commits: One logical change per commit, reference FR number
• •Review Before Merge: Phase X.2 catches issues early
• •Commit Discipline: Follow the sequence in Commit Discipline section
• •Checklist Discipline: Update immediately after completing each item
• •Documentation Current: Update checklist and FEATURE.md before completion
• •Parallelize independent FRs - Use sub-agents for FRs with no dependencies
• •Wave-based execution - Group FRs by dependency depth, execute waves in parallel
• •Integration verification - Always run full test suite after parallel implementation