Genesis Feature

---
name: "Feature"
description: Write the feature design doc — the WHY + SHAPE for a single feature. No formal requirements yet (those come in /genesis-specify).
argument-hint: "<feature-name> [--update|--fresh]"
---

# Feature — The WHY + SHAPE

Write the **feature design doc**: why this feature exists, what shape it takes, how it fits the project. It contains no formal requirements, acceptance criteria, or user stories — those come in `/genesis-specify`. This is the first per-feature pipeline command after that feature's brainstorm.

**Gate:** the feature's **brainstorm phase must be accepted** in `approvals/master.json` (else "Run /genesis-brainstorm and accept it first"). Also requires the project overview to exist.

## Inputs

- `.genesis/project-state.md` (mode)
- The constitution
- `.genesis/design/overview.md` (required), plus `architecture.md`, `data-model.md`, and other design docs
- `.genesis/features/<feature>/brainstorm-log.md` (required)
- `.genesis/features/<feature>/approvals/master.json` (verify brainstorm accepted)

## Process

1. Resolve the feature name; verify brainstorm accepted.
2. Handle an existing/partial doc (revise vs continue vs fresh).
3. Create the feature branch (named for the feature) if not already on one, and create `.genesis/features/<feature>/`.
4. Write `design.md` from `feature-design-template.md`. Sections: Overview · Business Rules · User Experience · Edge Cases · Error Handling · Data Requirements · Security Considerations · Performance Considerations · System Diagram · Technology Choices · Design Decisions (institutional memory) · Scope · Future Considerations — plus mode-specific sections.
5. Cross-reference project docs for contradictions and terminology; flag architectural discoveries that may require updating the project architecture doc.
6. **Self-validation pass** (up to 3 iterations): flag vague business rules, missing mode-specific sections, scope creep beyond the brainstorm, contradictions with architecture, empty/placeholder sections; auto-correct and report.
7. Constitution-compliance check; present for review; commit on the feature branch.

## Mode differences

- **Greenfield:** technical architecture / component breakdown.
- **Brownfield:** add **Existing System Analysis** and a **Scope Boundary Map** (what changes vs what stays); use git blame for ownership.
- **Lowfield:** process design — **Pipeline Table Design, Artifact Schema Design, Domain Vocabulary**.

## Output

- `.genesis/features/<feature>/design.md` — the WHY + SHAPE document.

## Next step

Run `/genesis-specify`.

## Natural language triggers

```
- "write the feature design"
- "shape this feature"
- "feature doc for X"
```