PRD to Plan

Break a PRD into phased vertical slices (tracer bullets). Output: plans/<name>.md.

Pre-loaded context

Before proceeding, use the Glob tool to list files in prds/ directory.

Workflow

1. Read the PRD

Open the PRD file. If no name given, ask: "Which PRD should we plan?" — list each available PRD as an option. Use AskUserQuestion when available; otherwise present as a numbered list.

2. Explore the codebase

Understand current architecture, existing patterns, and integration points.

3. Identify durable architectural decisions

Before slicing, extract decisions that hold across all phases:

• Route structures / URL patterns
• Database schema shape
• Key data models and definitions
• Auth/authorization approach
• Third-party service boundaries

4. Draft vertical slices

Each phase is a thin tracer bullet -- a narrow but complete path through every integration layer (schema, service, API, UI, tests). A completed phase is demoable on its own.

Deriving tasks from the PRD:

PRD Section	Becomes
New Modules	Implement module with interface
Schema Changes	Migration + validation
API Contracts	Route returning shape
Navigation	Wire component to route
User Stories	Verify coverage; add task if missing
Testing Decisions	Tests land in the phase where their module lands
Out of Scope	Never create tasks for these

Within each slice, order by dependency: schema -> service -> API -> UI -> tests. Happy paths before edge cases.

Phase naming: use a goal phrase answering "what can we demo when this is done?" (e.g., "Phase 1 -- Revenue visible end-to-end"), not a layer name.

When to use layer-by-layer instead: If the PRD has complex schema changes that all modules depend on and no single user story can stand alone without the full schema, build the data foundation first, then slice the rest vertically.

Phase count: 2-3 for single-module, 3-5 for multi-module, 5+ means consider splitting the PRD.

5. Quiz the user

Present the breakdown. For each phase show:

• Title: short goal phrase
• User stories covered: which PRD stories this addresses
• Done when: the testable condition

Ask: "Does the phase breakdown look right?" — Options: "Looks good, proceed (Recommended)", "Merge some phases", "Split some phases", "Reorder phases". Use AskUserQuestion when available; otherwise present as numbered options. Iterate until approved.

6. Save plan

Save to plans/<same-stem-as-prd>.md (create plans/ if missing).

# Plan: <Feature Name>

> Source PRD: `prds/<name>.md`

## Architectural decisions

Durable decisions that apply across all phases:

- **Routes**: ...
- **Schema**: ...
- **Key models**: ...

---

## Phase 1 -- <Goal>

**User stories**: <list from PRD>

### What to build

Concise description of this vertical slice -- end-to-end behavior, not layer-by-layer.

### Done when

<Specific, testable condition. e.g., "Instructor sees total revenue for a course; service tests pass against in-memory DB.">

---

<!-- Repeat for each phase -->

## Out of Scope

Carried forward from PRD verbatim.

## Open Questions

Gaps found in the PRD needing resolution. Blank if none.

Print saved path and one line per phase: Phase N -- <title> (<condition summary>).

Rules

• Phases derive from PRD user stories -- never invented
• Each phase must be demoable end-to-end on its own
• "Done when" must be testable, not vague
• Never modify the source PRD
• Carry PRD's Out of Scope forward verbatim

Error Handling

• PRD not found -- list available PRDs and ask
• PRD missing sections -- note gaps inline and continue
• plans/ missing -- create it