# 0021 — Implement skills: implement-feature, tdd, refactor, write-docs, diagnose

**Type:** HITL  
**Parent PRD:** `docs/prd/chunk-3-skills-library.md`

## What to build

The 5 implement phase skills. Two are new; three are preserved Pocock placeholders upgraded to the authoring standard. All authored via `write-skill` (0018), evals via `write-eval` (0017).

**Skills, origins, and trigger descriptions:**

| Flat name | Origin | Trigger description |
|---|---|---|
| `implement-feature` | New | Implement a feature, build this, write the code for X |
| `tdd` | Preserved; frontmatter + standard added | TDD, test-driven, red-green-refactor |
| `refactor` | New | Refactor this code, improve structure, clean up |
| `write-docs` | New | Write documentation, add docstrings, generate README |
| `diagnose` | Preserved; frontmatter + standard added | Diagnose this, what's wrong with X, debug this |

**Key constraints per skill:**
- `implement-feature`: must start from a linked issue with an EARS spec (checks `docs/issues/` in the file-based phase, Gitea MCP when configured); flags if none exists; no unrequested abstractions; updates `docs/spec/` as part of implementation if behaviour changes; calls `tdd` as its implementation methodology
- `tdd`: composable and separate from `implement-feature` so TDD can be used outside full feature implementation; red-green-refactor loop
- `refactor`: preserves all existing behaviour; documents what changed and why
- `write-docs`: derives from code and spec; never invents behaviour
- `diagnose`: preserved behavior; add frontmatter, authoring standard sections, and dead-reference cleanup

## Implementation notes

Follow the per-skill workflow defined in `docs/notes/skill-implementation-workflow.md` (produced by issue 0016).

**Known upstream sources to review for this category:**
- `mattpocock/skills` — original `tdd` and `diagnose` placeholders; review at current HEAD; record SHAs in `source:` for any adopted content
- `bmad-method/bmad-method` — BMAD developer role and implementation patterns; relevant for `implement-feature` and `refactor`

For new skills (`implement-feature`, `refactor`, `write-docs`): search for prior art in the above repos before writing from scratch.

## Acceptance criteria

- [ ] All 5 SKILL.md files exist at `.agents/skills/<skill-name>/SKILL.md`; `metadata.category: implement`; authoring standard met
- [ ] Dead references removed from Pocock skills (`tdd`, `diagnose`)
- [ ] `implement-feature` checks for linked issue with EARS spec before proceeding; calls `tdd` by name
- [ ] `source:` fields populated for adopted upstream content
- [ ] Each skill has a co-located eval at `.agents/evals/implement/<skill-name>/eval.yaml` via `write-eval`
- [ ] `install.sh` deploys all 5 to `~/.agents/skills/`
- [ ] **HITL:** human runs behavioral test per skill
- [ ] **HITL:** human reviews each SKILL.md and eval before committing
- [ ] _(Further criteria to be refined after issue 0016 grill session)_

## Blocked by

- 0016 (per-skill workflow)
- 0017 (`write-eval`)
- 0018 (`write-skill`)