feat: Add exact scheme specification for TON networks

[EruditeIntelligence]

feat: Add exact scheme specification for TON networks

Summary

This PR adds the scheme_exact_ton.md specification for The Open Network (TON) support within the x402 protocol. TON features ~5 second finality, Ed25519 signatures, BOC serialization, and Jetton (TEP-74) fungible token support.

Key design decisions

• BOC (Bag of Cells) serialization: Client signs wallet messages with Ed25519, serialized as BOC
• CAIP-2 identifiers: ton:mainnet, ton:testnet
• Denomination: Amounts in nanotons (1 TON = 1,000,000,000 nanotons)
• Jetton support: TEP-74 standard for USDT/USDC transfers on TON
• valid_until expiry: Time-based expiration with max 120-second window

Reference implementation

A complete JavaScript SDK is published and available:

• npm: @erudite-intelligence/x402-ton
• MIT licensed

Checklist

• Spec follows existing scheme_exact_evm.md format and structure
• CAIP-2 network identifiers documented
• Payment requirements format specified
• Payment payload format specified
• Client flow documented
• Facilitator verification flow documented
• Facilitator settlement flow documented
• Security considerations addressed
• Trust model explicitly documented
• TOCTOU mitigation specified
• Settlement failure modes documented
• Reference implementation published on npm
• Commits signed

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[vercel]

@EruditeIntelligence is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[phdargen]

Duplicate of https://github.com/coinbase/x402/pull/1455, please comment on the existing proposal instead