feat(ruby): Add complete Ruby SDK implementation for x402 protocol

[mfix-stripe]

Implements a full-featured Ruby SDK with feature parity to the Python SDK, following repository conventions and Ruby idioms.

Core Components:

• X402::Client - Payment creation with policy system and lifecycle hooks
• X402::ResourceServer - Resource protection with verification/settlement
• X402::Facilitator - Payment verification and on-chain settlement

Blockchain Support:

• EVM mechanism (production-ready):
  • EIP-3009 TransferWithAuthorization for USDC
  • EIP-712 typed data signing
  • Networks: Ethereum, Base, Polygon, Avalanche, MegaETH
  • Private key signer with eth gem
• SVM mechanism (simplified):
  • Solana transaction support
  • Networks: mainnet, devnet, testnet
  • Ed25519 signing

HTTP Integration:

• Faraday-based facilitator client
• Rack middleware for universal web framework support
• Base64 encoding/decoding utilities
• Rails integration ready

Type System:

• dry-struct + dry-types for runtime validation
• Automatic camelCase JSON serialization
• Immutable data structures
• Protocol-based interfaces using Ruby modules

Features:

• Policy system (prefer_network, prefer_scheme, max_amount)
• Lifecycle hooks (before/after/on_failure) for all operations
• Network pattern matching with wildcards (eip155:*)
• CAIP-2 network identifier support (V2 protocol)
• Graceful degradation for optional dependencies

Testing:

• Comprehensive unit tests (Client, Server, Facilitator, Schemas)
• Integration tests for full payment flow
• Mock payment scheme for testing
• SimpleCov coverage reporting (80% target)
• RSpec configuration with VCR for HTTP fixtures

Documentation:

• README.md with installation and quick start
• CLIENT.md - Complete client implementation guide
• SERVER.md - Server setup and middleware integration
• FACILITATOR.md - Deployment and operations guide
• CONTRIBUTING.md - Development workflow and guidelines
• CHANGELOG.md - Version history

Examples:

• client_basic/ - Basic client with payment creation
• server_rack/ - Rack server with payment-protected routes
• facilitator/ - Simple facilitator service with Sinatra

Build Configuration:

• gemspec with core and optional dependencies
• Rakefile with test, lint, and doc tasks
• Bundler groups for optional features (evm, svm, dev)

Dependencies:

• Core: dry-struct, dry-types, faraday
• Optional EVM: eth (~> 0.5)
• Optional SVM: base58, ed25519
• Optional Web: rack, sinatra, rails
• Dev: rspec, rubocop, yard, webmock, vcr, simplecov

Note: ETH addresses are public USDC contract addresses. Email addresses are public project contact information.

GIT_VALID_PII_OVERRIDE

Committed-By-Agent: claude

Description

Tests

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits
• I added a changelog fragment for user-facing changes (docs-only changes can skip)

[cb-heimdall]

🟡 Heimdall Review Status

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