Implement the 006-pre-commit-gate feature that enforces a pre-commit quality gate using Lefthook to run pnpm check before every commit

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/006-pre-commit-gate/tasks.md

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+# Tasks: Pre-Commit Gate
+
+**Input**: Design documents from `/specs/006-pre-commit-gate/`
+**Prerequisites**: plan.md (required), spec.md (required for user stories), research.md, quickstart.md
+
+**Tests**: No test tasks included (not requested in feature specification). Verification is manual.
+
+**Organization**: Tasks are grouped by user story to enable independent implementation and testing of each story.
+
+## Format: `[ID] [P?] [Story] Description`
+
+- **[P]**: Can run in parallel (different files, no dependencies)
+- **[Story]**: Which user story this task belongs to (e.g., US1, US2, US3)
+- Include exact file paths in descriptions
+
+## Phase 1: Setup (Shared Infrastructure)
+
+**Purpose**: Install Lefthook and configure auto-install mechanism
+
+- [x] T001 Add `lefthook` as a devDependency and add a `prepare` script that runs `lefthook install` in `package.json`
+- [x] T002 Run `pnpm install` to install lefthook and activate the prepare script
+
+**Checkpoint**: `lefthook` is installed and `pnpm install` triggers `lefthook install` automatically
+
+---
+
+## Phase 2: User Story 1 & 2 - Block Failing / Allow Passing Commits (Priority: P1) MVP
+
+**Goal**: Create the Lefthook pre-commit hook configuration that runs `pnpm check`, blocking commits on failure and allowing commits on success.
+
+**Independent Test (US1)**: Introduce a deliberate lint error, run `git commit`, and verify the commit is blocked with visible error output.
+
+**Independent Test (US2)**: Make a valid change, run `git commit`, and verify the commit succeeds after `pnpm check` passes.
+
+### Implementation
+
+- [x] T003 [US1] [US2] Create `lefthook.yml` at repository root with a `pre-commit` hook that runs `pnpm check`
+
+**Checkpoint**: Commits are blocked when `pnpm check` fails (US1) and allowed when it passes (US2). Output from `pnpm check` is visible to the developer.
+
+---
+
+## Phase 3: User Story 3 - Bypass Gate in Emergencies (Priority: P2)
+
+**Goal**: Ensure the standard `git commit --no-verify` flag bypasses the pre-commit hook.
+
+**Independent Test**: Stage a change that would fail checks, run `git commit --no-verify`, and verify the commit succeeds without running checks.
+
+### Implementation
+
+No implementation task needed -- Lefthook respects `--no-verify` by default (standard Git behavior). This phase exists for verification only.
+
+**Checkpoint**: `git commit --no-verify` bypasses the pre-commit gate.
+
+---
+
+## Phase 4: Polish & Cross-Cutting Concerns
+
+**Purpose**: Edge case handling and validation
+
+- [x] T004 Verify the hook provides a clear error when `pnpm` is not in PATH (FR-007) and when `node_modules` are missing (edge case)
+- [x] T005 Run quickstart.md validation: clone-install-commit workflow works end-to-end (SC-003)
+
+---
+
+## Dependencies & Execution Order
+
+### Phase Dependencies
+
+- **Setup (Phase 1)**: No dependencies -- start immediately
+- **US1 & US2 (Phase 2)**: Depends on Phase 1 (lefthook must be installed)
+- **US3 (Phase 3)**: No implementation needed -- verify after Phase 2
+- **Polish (Phase 4)**: Depends on Phase 2 completion
+
+### Parallel Opportunities
+
+- T001 and T003 touch different files (`package.json` vs `lefthook.yml`) but T003 depends on lefthook being installed, so they must be sequential.
+- T004 and T005 can run in parallel after Phase 2.
+
+---
+
+## Implementation Strategy
+
+### MVP First (User Stories 1 & 2)
+
+1. Complete Phase 1: Install lefthook + prepare script
+2. Complete Phase 2: Create `lefthook.yml` with pre-commit hook
+3. **STOP and VALIDATE**: Test both blocking and allowing commits
+4. Verify US3 bypass works (no implementation needed)
+
+### Execution Summary
+
+Total: **5 tasks** across 4 phases
+- Phase 1 (Setup): 2 tasks
+- Phase 2 (US1 + US2): 1 task
+- Phase 3 (US3): 0 tasks (verification only)
+- Phase 4 (Polish): 2 tasks
+
+---
+
+## Notes
+
+- US1 and US2 are implemented by the same single task (T003) because they are two sides of the same coin: the hook either blocks or allows based on `pnpm check` exit code.
+- US3 requires no implementation -- `--no-verify` is standard Git behavior that Lefthook respects.
+- This is a minimal-footprint feature: 1 new file (`lefthook.yml`), 1 modified file (`package.json`).