Scaffold Rework Implementation Prompt

# Implementation Prompt: `scaffold rework` Command

Copy everything below the line and paste it as a prompt to Claude Code.

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## Task

Implement the `scaffold rework` CLI command as specified in `docs/superpowers/specs/2026-03-29-scaffold-rework-command-design.md`. Read that spec first — it is the authoritative source for all behavior. This prompt provides implementation-level guidance on top of the spec.

## Context

This is a new CLI subcommand for the scaffold pipeline tool. It lets users re-run all steps within selected phases — either to improve artifact depth or clean up a messy run. The command creates a persistent execution plan (`.scaffold/rework.json`) that the scaffold-runner skill reads to drive step-by-step execution.

**Approach:** Hybrid — the CLI handles phase selection and session management (planner), the runner skill handles step execution (executor).

## Implementation Order

Follow TDD. For each file below: write failing tests first, then implement until tests pass, then move to the next file.

### Step 1: Types (`src/types/rework.ts`)

Define the TypeScript interfaces for the rework session. Add a re-export in `src/types/index.ts`.