# Implementation Plan: Pre-Commit Gate

**Branch**: `006-pre-commit-gate` | **Date**: 2026-03-05 | **Spec**: [spec.md](./spec.md)
**Input**: Feature specification from `/specs/006-pre-commit-gate/spec.md`

## Summary

Enforce a pre-commit quality gate by adding Lefthook as a Git hooks manager. A `lefthook.yml` configuration defines a pre-commit hook that runs `pnpm check`. The hook auto-installs via a `prepare` script in `package.json`, ensuring zero manual setup for developers after `pnpm install`.

## Technical Context

**Language/Version**: TypeScript 5.x (project), Go binary via npm (Lefthook)
**Primary Dependencies**: `lefthook` (npm devDependency)
**Storage**: N/A
**Testing**: Manual verification (commit with passing/failing checks)
**Target Platform**: macOS, Linux (developer workstations)
**Project Type**: Monorepo (pnpm workspaces) -- web application with domain/application/web layers
**Performance Goals**: No additional overhead beyond `pnpm check` execution time
**Constraints**: Must auto-install on `pnpm install`; must not interfere with CI
**Scale/Scope**: 2 files changed (lefthook.yml created, package.json modified)

## Constitution Check

*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*

| Principle | Status | Notes |
|-----------|--------|-------|
| I. Deterministic Domain Core | N/A | No domain logic changes |
| II. Layered Architecture | PASS | Tooling-only change, no layer imports affected |
| III. Agent Boundary | N/A | No agent layer changes |
| IV. Clarification-First | PASS | User explicitly specified Lefthook; no ambiguity |
| V. Escalation Gates | PASS | Feature is within spec scope |
| VI. MVP Baseline Language | PASS | No permanent bans introduced |
| VII. No Gameplay Rules | N/A | Not a gameplay feature |
| Development Workflow (merge gate) | PASS | Directly implements the "automated checks must pass" rule |
| Layer boundary compliance | N/A | No source code layer changes |

**Post-design re-check**: All gates still pass. No design decisions introduced new violations.

## Project Structure

### Documentation (this feature)

```text
specs/006-pre-commit-gate/
├── plan.md              # This file
├── research.md          # Phase 0 output
├── quickstart.md        # Phase 1 output
├── spec.md              # Feature specification
└── checklists/
    └── requirements.md  # Spec quality checklist
```

### Source Code (repository root)

```text
./
├── lefthook.yml         # NEW — Lefthook configuration (pre-commit hook)
├── package.json         # MODIFIED — add lefthook devDep + prepare script
└── (all existing files unchanged)
```

**Structure Decision**: This feature only adds tooling configuration at the repository root. No source code directories are created or modified. The existing monorepo structure (`packages/*`, `apps/*`) is unchanged.

## Complexity Tracking

No constitution violations. Table not applicable.