feat: Add JSON Schema definitions for AP2 mandate types

[ne275]

Description

This PR adds language-agnostic JSON Schema definitions for all AP2 mandate types, addressing the need for Verifiable Credential support in non-Python implementations.

Changes

• ✅ Add JSON Schema files for IntentMandate, CartMandate, and PaymentMandate
  • schemas/intent-mandate.schema.json
  • schemas/cart-mandate.schema.json
  • schemas/payment-mandate.schema.json
• ✅ Create automated schema generation script (scripts/generate_schemas.py)
  • Uses Pydantic's model_json_schema() to ensure schemas stay in sync with Python types
  • Adds proper $schema and $id fields for JSON Schema compliance
• ✅ Add schema validation test script (scripts/validate_schemas.py)
• ✅ Add comprehensive documentation (schemas/README.md)
  • Usage examples for Python, JavaScript/TypeScript, and Go
  • Instructions for type generation with tools like quicktype
  • Guidance for using schemas with Verifiable Credentials
• ✅ Update main README with JSON Schema support section

Problem Solved

Previously, AP2 only provided Python type definitions (Pydantic models), which created barriers for:

• Non-Python implementations
• Verifiable Credential issuers who need portable, verifiable schema definitions
• Cross-language validation and type generation
• IDE autocomplete and validation in other languages

Solution Benefits

These schemas enable:

• ✅ Validation of mandate objects in any programming language
• ✅ Type generation for non-Python implementations (TypeScript, Go, Swift, Kotlin, etc.)
• ✅ Verifiable Credential creation with proper schema references
• ✅ IDE support with autocomplete and validation
• ✅ Interoperability across different implementations

Schema URLs

Schemas are publicly accessible at:
https://raw.githubusercontent.com/google-agentic-commerce/AP2/main/schemas/intent-mandate.schema.json
https://raw.githubusercontent.com/google-agentic-commerce/AP2/main/schemas/cart-mandate.schema.json
https://raw.githubusercontent.com/google-agentic-commerce/AP2/main/schemas/payment-mandate.schema.json

Testing

• Schemas generate successfully from Pydantic models
• IntentMandate schema validates example instances
• All files include proper Apache 2.0 license headers
• Documentation includes working examples for multiple languages

Checklist

• Follow the CONTRIBUTING Guide
• Make Pull Request title follow Conventional Commits specification
• Ensure the tests and linter pass
• Appropriate docs were updated

Fixes #127

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[gemini-code-assist]

Summary of Changes

Hello @ne275, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the interoperability of the AP2 protocol by introducing language-agnostic JSON Schema definitions for its core mandate types (Intent, Cart, and Payment). This change addresses previous limitations where only Python type definitions were available, thereby enabling broader adoption across non-Python implementations, facilitating Verifiable Credential support, and improving cross-language validation and type generation. The new schemas provide a standardized way to define and validate AP2 mandate objects, fostering a more robust and accessible ecosystem.

Highlights

• JSON Schema Definitions: Added language-agnostic JSON Schema files for IntentMandate, CartMandate, and PaymentMandate, enabling broader interoperability.
• Automated Schema Generation: Introduced a Python script (scripts/generate_schemas.py) that leverages Pydantic's model_json_schema() to ensure the generated schemas remain synchronized with the Python type definitions.
• Schema Validation Script: Included a new script (scripts/validate_schemas.py) to automatically validate the generated JSON schemas against example instances, ensuring their correctness.
• Comprehensive Documentation: Added a detailed schemas/README.md, providing usage examples for validation in Python, JavaScript/TypeScript, and Go, along with instructions for type generation and integration with Verifiable Credentials.
• Main README Update: The main README.md has been updated with a new section dedicated to JSON Schema support, outlining its benefits and linking to the new schema documentation.

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[gemini-code-assist]

Code Review

This is a great addition to the project! Providing JSON schemas significantly improves interoperability and makes it easier for developers using other languages to adopt AP2. The generation and validation scripts are excellent for ensuring the schemas stay in sync with the Pydantic models.

I've left a few suggestions to further improve the generated schemas and the documentation examples. Specifically, I've recommended:

• Fixing the Go example in the schemas/README.md to be runnable.
• Improving the schema generation script to clean up descriptions and add date-time formats.
• Making the validation script's dependency handling more user-friendly.

Overall, this is a very solid and valuable contribution. Well done!