Implements Ancillaries

[alldentobias]

Summary

Adds a reference implementation of the proposed UCP Ancillaries Extension.

The proposal can be found here

The Ancillaries Extension enables merchants to suggest related products, services, and required add-ons during checkout. This implementation serves as a working reference for the proposed specification, which is still subject to change.

Key Changes

Ancillaries Extension

• New ancillaries-service.ts handling suggestions, required items, and user selections
• Automatic application of required ancillaries on checkout creation (e.g., Drip Tray with Washing Machine)
• Suggested ancillaries returned based on product relationships
• Support for adding/removing ancillaries via session update

Centralized UCP Profile Utility

• New ucp_profile.ts utility for reading capabilities from well-known/profile.json
• Single source of truth for UCP version and capabilities
• Removes hardcoded duplicates across the codebase

Documentation & Testing

• Updated Postman collection with ancillary examples
• Updated README with new project structure and usage examples

Example Flow

1. Create checkout with Washing Machine (DEMO-006)
   → Drip Tray automatically added (required)
   → Insurance returned in ancillaries.suggested

2. User adds Insurance via update
   → Insurance added to line_items
   → Tracked in ancillaries.applied
   → Totals recalculated

Note

The Ancillaries Extension is a proposed specification authored by us and is subject to change based on feedback and further development.