SYSTEM
You are 秒搭 Document Builder.
Return only one JSON object.
The JSON schema is:
{
  "title": string,
  "subtitle": string,
  "summary": string,
  "sections": [
    { "heading": string, "paragraphs": string[] }
  ]
}
Requirements:
- Produce 4 to 7 sections total.
- Each section must have 1 to 3 concise, publication-ready paragraphs.
- Make the document usable as a real deliverable, not a chat transcript.
- Close with a concrete next-step or recommendation section.
- If the briefing looks like a product spec or PRD, prefer headings such as Problem Statement, Goals, Non-goals, Requirements, Success Metrics, Open Questions, and Timeline.

USER
Session title: Invoice Template for Freelancers and Independent Contractors
Session id: document-en-us-invoice-template-for-freelancers-and-independent-contractors
Rounds: 4
Messages: 8
Linked knowledge files: 0

Conversation digest:
Example objective: Build a polished document or template that can be reused as a real operating artifact.
Topic title: Invoice Template for Freelancers and Independent Contractors
Target audience: Freelancers, gig workers, and independent contractors
Industry: Freelance and Creative Services
Locale: en-US
Region: United States
Search intent: Users need a downloadable invoice sample that looks professional and includes standard billing fields for U.S. clients.
SEO keywords: freelance invoice template, contractor invoice example, invoice sample, self employed invoice, professional invoice document
Regional nuance: Tailored to U.S. billing norms with invoice number, due date, payment terms, line items, tax field options, and payment method details.
Market notes: Favor clarity, conversion language, ROI framing, and concise calls to action.
Template hint: Create a clean invoice format with branding header, client and vendor information, itemized charges, subtotal, tax, total due, and payment instructions.

Linked knowledge digest:
No linked knowledge files.

Recent memory digest:
No recent memory summaries.

Generate a high-quality document spec now.