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# Spec-Driven Implementation

## Overview

Implement features from validated specifications using Test-Driven Development, with continuous spec compliance checking throughout.

This is the core SDD implementation workflow: Spec → Plan → TDD → Verify.

**Critical Rule:** Implementation MUST match spec. Any deviation triggers spec evolution workflow.

## When to Use

**Use this skill when:**
- Spec exists and is validated
- Ready to write code
- Starting implementation of new feature

**Don't use this skill when:**
- No spec exists → Use `sdd:spec` or `sdd:brainstorm` first
- Spec/code mismatch exists → Use `sdd:evolve`
- Debugging existing code → Use `systematic-debugging`

## Technical Prerequisites

Ensure spec-kit is initialized:

{Skill: spec-kit}

If spec-kit prompts for restart, pause this workflow and resume after restart.

## Workflow Prerequisites

**Before starting implementation:**
- [ ] Spec exists in `specs/features/[feature-name].md`
- [ ] Spec validated for soundness (`sdd:review-spec`)
- [ ] Spec validated against constitution (if exists)
- [ ] No open questions in spec that block implementation

**If prerequisites not met:** Stop and address them first.

## The Process

### 1. Read and Understand Spec

**Load the spec:**
```bash
cat specs/features/[feature-name].md
```

**Extract key information:**
- Functional requirements (what to build)
- Success criteria (how to verify)
- Error handling (what can go wrong)
- Dependencies (what's needed)
- Constraints (limitations)

**Validate understanding:**
- Summarize spec back to user
- Confirm no ambiguities remain
- Identify any implementation questions

### 2. Generate Implementation Plan FROM Spec

**Use `sdd:writing-plans` skill** to create plan.

**The plan MUST:**
- Derive directly from spec requirements
- Include all functional requirements
- Cover all error cases
- Address all edge cases
- Reference spec sections explicitly

**Plan structure:**
```markdown
# Implementation Plan: [Feature Name]

**Sou