You are a senior product manager. Create a comprehensive Product Requirements
Document (PRD) for the following project.

## Input

**Problem statement:**
{{problem_statement}}

**Stakeholders:**
{{stakeholders}}

**Known constraints:**
{{constraints}}

## Output requirements

Produce a Markdown PRD with these sections in order:

1. **Overview** - 2-3 sentence summary
2. **Problem statement** - the "why" with concrete examples
3. **Goals & non-goals** - bulleted, clear, measurable goals + explicit non-goals
4. **Target users** - primary, secondary, tertiary user segments
5. **Key user journeys** - 3-5 end-to-end flows in numbered steps
6. **Functional requirements** - grouped into Must-have / Should-have / Nice-to-have
7. **Non-functional requirements** - performance, security, accessibility, scale
8. **Success metrics** - how we'll measure if this worked
9. **Constraints & assumptions** - what we're taking as given
10. **Out of scope** - explicit list of what this project will NOT do
11. **Open questions** - decisions still needed, with proposed answers

## Style guide

- Use second-person voice ("the user wants...")
- Numbers and metrics over adjectives ("loads in <2s" not "fast")
- Concrete examples over abstractions
- Call out risks and unknowns explicitly
- If you have to assume something, label it "Assumption: ..."

## Length

- Target: 800-1500 words
- If the problem is genuinely complex, go longer but stay structured

# PRD - Customer Portal v1

## 1. Overview

A self-service customer portal that lets enterprise customers manage their
subscriptions, view invoices, and submit support tickets without contacting
their account manager.

## 2. Problem statement

Today, 40% of inbound account-manager requests are routine self-service
tasks (password resets, invoice downloads, plan changes). This costs the
support team ~120 hours/week and creates friction for customers who want
quick answers...