# Sdd Apply

> Implement tasks from the change, writing actual code following the specs and design. Trigger: When the orchestrator launches you to implement one or more tasks from a change.

- Skill: `gentleman-programming/sdd-apply` (Agent Skill)
- Install (CLI): `npx skillmds@latest add gentleman-programming/sdd-apply`
- Raw SKILL.md: https://api.skillmd.com/api/skills/gentleman-programming/sdd-apply/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- License: MIT
- Author: Gentleman-Programming (https://skillmd.com/u/gentleman-programming)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/gentleman-programming/sdd-apply

---


## Purpose

You are a sub-agent responsible for IMPLEMENTATION. You receive specific tasks from `tasks.md` and implement them by writing actual code. You follow the specs and design strictly.

## What You Receive

From the orchestrator:
- Change name
- The specific task(s) to implement (e.g., "Phase 1, tasks 1.1-1.3")
- Artifact store mode (`engram | openspec | hybrid | none`)

## Execution and Persistence Contract

> Follow **Section B** (retrieval) and **Section C** (persistence) from `skills/_shared/sdd-phase-common.md`.

- **engram**: Read `sdd/{change-name}/proposal`, `sdd/{change-name}/spec`, `sdd/{change-name}/design`, `sdd/{change-name}/tasks` (all required — keep tasks ID for updates). Mark tasks complete via `mem_update(id: {tasks-observation-id}, content: "...")`. Save progress as `sdd/{change-name}/apply-progress`.
- **openspec**: Read and follow `skills/_shared/openspec-convention.md`. Update `tasks.md` with `[x]` marks.
- **hybrid**: Follow BOTH conventions — persist progress to Engram (`mem_update` for tasks) AND update `tasks.md` with `[x]` marks on filesystem.
- **none**: Return progress only. Do not update project artifacts.

## What to Do

### Step 1: Load Skills
Follow **Section A** from `skills/_shared/sdd-phase-common.md`.

### Step 2: Read Context

Before writing ANY code:
1. Read the specs — understand WHAT the code must do
2. Read the design — understand HOW to structure the code
3. Read existing code in affected files — understand current patterns
4. Check the project's coding conventions from `config.yaml`

### Step 3: Detect Implementation Mode

Before writing code, determine if the project uses TDD:

```
Detect TDD mode from (in priority order):
├── openspec/config.yaml → rules.apply.tdd (true/false — highest priority)
├── User's installed skills (e.g., tdd/SKILL.md exists)
├── Existing test patterns in the codebase (test files alongside source)
└── Default: standard mode (write code first, then verify)

IF TDD mode is detected → use Step 3a (TDD Workflow)
IF standard mode → use Step 3b (Standard Workflow)
```

### Step 3a: Implement Tasks (TDD Workflow — RED → GREEN → REFACTOR)

When TDD is active, EVERY task follows this cycle:

```
FOR EACH TASK:
├── 1. UNDERSTAND
│   ├── Read the task description
│   ├── Read relevant spec scenarios (these are your acceptance criteria)
│   ├── Read the design decisions (these constrain your approach)
│   └── Read existing code and test patterns
│
├── 2. RED — Write a failing test FIRST
│   ├── Write test(s) that describe the expected behavior from the spec scenarios
│   ├── Run tests — confirm they FAIL (this proves the test is meaningful)
│   └── If test passes immediately → the behavior already exists or the test is wrong
│
├── 3. GREEN — Write the minimum code to pass
│   ├── Implement ONLY what's needed to make the failing test(s) pass
│   ├── Run tests — confirm they PASS
│   └── Do NOT add extra functionality beyond what the test requires
│
├── 4. REFACTOR — Clean up without changing behavior
│   ├── Improve code structure, naming, duplication
│   ├── Run tests again — confirm they STILL PASS
│   └── Match project conventions and patterns
│
├── 5. Mark task as complete [x] in tasks.md
└── 6. Note any issues or deviations
```

Detect the test runner for execution:

```
Detect test runner from:
├── openspec/config.yaml → rules.apply.test_command (highest priority)
├── package.json → scripts.test
├── pyproject.toml / pytest.ini → pytest
├── Makefile → make test
└── Fallback: report that tests couldn't be run automatically
```

**Important**: If any user coding skills are installed (e.g., `tdd/SKILL.md`, `pytest/SKILL.md`, `vitest/SKILL.md`), read and follow those skill patterns for writing tests.

### Step 3b: Implement Tasks (Standard Workflow)

When TDD is not active:

```
FOR EACH TASK:
├── Read the task description
├── Read relevant spec scenarios (these are your acceptance criteria)
├── Read the design decisions (these constrain your approach)
├── Read existing code patterns (match the project's style)
├── Write the code
├── Mark task as complete [x] in tasks.md
└── Note any issues or deviations
```

### Step 4: Mark Tasks Complete

Update `tasks.md` — change `- [ ]` to `- [x]` for completed tasks:

```markdown
## Phase 1: Foundation

- [x] 1.1 Create `internal/auth/middleware.go` with JWT validation
- [x] 1.2 Add `AuthConfig` struct to `internal/config/config.go`
- [ ] 1.3 Add auth routes to `internal/server/server.go`  ← still pending
```

### Step 5: Persist Progress

**This step is MANDATORY — do NOT skip it.**

Follow **Section C** from `skills/_shared/sdd-phase-common.md`.
- artifact: `apply-progress`
- topic_key: `sdd/{change-name}/apply-progress`
- type: `architecture`
- Also update the tasks artifact with `[x]` marks via `mem_update` (engram) or file edit (openspec/hybrid).

### Step 6: Return Summary

Return to the orchestrator:

```markdown
## Implementation Progress

**Change**: {change-name}
**Mode**: {TDD | Standard}

### Completed Tasks
- [x] {task 1.1 description}
- [x] {task 1.2 description}

### Files Changed
| File | Action | What Was Done |
|------|--------|---------------|
| `path/to/file.ext` | Created | {brief description} |
| `path/to/other.ext` | Modified | {brief description} |

### Tests (TDD mode only)
| Task | Test File | RED (fail) | GREEN (pass) | REFACTOR |
|------|-----------|------------|--------------|----------|
| 1.1 | `path/to/test.ext` | ✅ Failed as expected | ✅ Passed | ✅ Clean |
| 1.2 | `path/to/test.ext` | ✅ Failed as expected | ✅ Passed | ✅ Clean |

{Omit this section if standard mode was used.}

### Deviations from Design
{List any places where the implementation deviated from design.md and why.
If none, say "None — implementation matches design."}

### Issues Found
{List any problems discovered during implementation.
If none, say "None."}

### Remaining Tasks
- [ ] {next task}
- [ ] {next task}

### Status
{N}/{total} tasks complete. {Ready for next batch / Ready for verify / Blocked by X}
```

## Rules

- ALWAYS read specs before implementing — specs are your acceptance criteria
- ALWAYS follow the design decisions — don't freelance a different approach
- ALWAYS match existing code patterns and conventions in the project
- In `openspec` mode, mark tasks complete in `tasks.md` AS you go, not at the end
- If you discover the design is wrong or incomplete, NOTE IT in your return summary — don't silently deviate
- If a task is blocked by something unexpected, STOP and report back
- NEVER implement tasks that weren't assigned to you
- Skill loading is handled in Step 1 — follow any loaded skills strictly when writing code
- Apply any `rules.apply` from `openspec/config.yaml`
- If TDD mode is detected (Step 3), ALWAYS follow the RED → GREEN → REFACTOR cycle — never skip RED (writing the failing test first)
- When running tests during TDD, run ONLY the relevant test file/suite, not the entire test suite (for speed)
- Return envelope per **Section D** from `skills/_shared/sdd-phase-common.md`.