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+---
+name: prd-to-plan
+description: Turn a PRD into a multi-phase implementation plan using tracer-bullet vertical slices, saved as a local Markdown file in ./plans/. Use when user wants to break down a PRD, create an implementation plan, plan phases from a PRD, or mentions "tracer bullets".
+---
+
+# PRD to Plan
+
+Break a PRD into a phased implementation plan using vertical slices (tracer bullets). Output is a Markdown file in `./plans/`.
+
+## Process
+
+### 1. Confirm the PRD is in context
+
+The PRD should already be in the conversation. If it isn't, ask the user to paste it or point you to the file.
+
+### 2. Explore the codebase
+
+If you have not already explored the codebase, do so to understand the current architecture, existing patterns, and integration layers.
+
+### 3. Identify durable architectural decisions
+
+Before slicing, identify high-level decisions that are unlikely to change throughout implementation:
+
+- Route structures / URL patterns
+- Database schema shape
+- Key data models
+- Authentication / authorization approach
+- Third-party service boundaries
+
+These go in the plan header so every phase can reference them.
+
+### 4. Draft vertical slices
+
+Break the PRD into **tracer bullet** phases. Each phase is a thin vertical slice that cuts through ALL integration layers end-to-end, NOT a horizontal slice of one layer.
+
+<vertical-slice-rules>
+- Each slice delivers a narrow but COMPLETE path through every layer (schema, API, UI, tests)
+- A completed slice is demoable or verifiable on its own
+- Prefer many thin slices over few thick ones
+- Do NOT include specific file names, function names, or implementation details that are likely to change as later phases are built
+- DO include durable decisions: route paths, schema shapes, data model names
+</vertical-slice-rules>
+
+### 5. Quiz the user
+
+Present the proposed breakdown as a numbered list. For each phase show:
+
+- **Title**: short descriptive name
+- **User stories covered**: which user stories from the PRD this addresses
+
+Ask the user:
+
+- Does the granularity feel right? (too coarse / too fine)
+- Should any phases be merged or split further?
+
+Iterate until the user approves the breakdown.
+
+### 6. Write the plan file
+
+Create `./plans/` if it doesn't exist. Write the plan as a Markdown file named after the feature (e.g. `./plans/user-onboarding.md`). Use the template below.
+
+<plan-template>
+# Plan: <Feature Name>
+
+> Source PRD: <brief identifier or link>
+
+## Architectural decisions
+
+Durable decisions that apply across all phases:
+
+- **Routes**: ...
+- **Schema**: ...
+- **Key models**: ...
+- (add/remove sections as appropriate)
+
+---
+
+## Phase 1: <Title>
+
+**User stories**: <list from PRD>
+
+### What to build
+
+A concise description of this vertical slice. Describe the end-to-end behavior, not layer-by-layer implementation.
+
+### Acceptance criteria
+
+- [ ] Criterion 1
+- [ ] Criterion 2
+- [ ] Criterion 3
+
+---
+
+## Phase 2: <Title>
+
+**User stories**: <list from PRD>
+
+### What to build
+
+...
+
+### Acceptance criteria
+
+- [ ] ...
+
+<!-- Repeat for each phase -->
+</plan-template>