feat(express): add EdDSA MPCv2 external signer routing

[vibhavgo]

Add Express routing for EdDSA MPCv2 external signer share generation. Wire MPCv2 wallet signing params to use the EdDSA round generators.

• Route EddsaMPCv2Round1/2/3 share requests to offline helpers
• Add EdDSA MPCv2 external signer generator factories
• Add typed route response codecs for EdDSA MPCv2 share responses
• Cover route dispatch, generator requests, and signing-param wiring
• Avoid external signer test fixture rewrites during test imports

Ticket: WCI-380

[linear-code]

WCI-380

[pranavjain97]

@claude

[github-actions]

Claude finished @pranavjain97's task —— View job

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Code Review Complete ✅

Reviewing the PR changes for EdDSA MPCv2 external signer routing implementation.

Todo List:

• Read and analyze the changed files
• Review implementation against PR requirements
• Check code quality and best practices
• Verify test coverage
• Provide comprehensive feedback

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Review Summary

This PR successfully implements EdDSA MPCv2 external signer routing by adding support for the three-round EdDSA MPCv2 signing protocol alongside the existing EdDSA v1 protocol. The implementation is well-structured and follows established patterns.

✅ Strengths

1. Comprehensive Implementation

• Multi-protocol support: Correctly handles both EdDSA v1 (commitment/R/G shares) and EdDSA MPCv2 (Round1/2/3) protocols
• Proper routing: Routes share requests to appropriate offline helpers based on multisigTypeVersion
• Complete coverage: Implements all three MPCv2 rounds (EddsaMPCv2Round1, EddsaMPCv2Round2, EddsaMPCv2Round3)

2. Code Quality & Architecture

• Consistent patterns: New generator functions follow the exact same structure as existing ECDSA MPCv2 generators
• Proper abstractions: Uses EddsaMPCv2Utils class for cryptographic operations
• Type safety: Comprehensive type definitions in generateShareTSS.ts with detailed documentation
• URL construction: Consistent REST endpoint patterns (/api/v2/{coin}/tssshare/EddsaMPCv2Round{1|2|3})

3. Backward Compatibility

• Non-breaking: EdDSA v1 functionality remains unchanged
• Version detection: Uses wallet._wallet.multisigTypeVersion === 'MPCv2' for proper routing
• Graceful fallbacks: Maintains existing behavior for non-MPCv2 wallets

4. Excellent Test Coverage

• Unit tests: 273 new test lines covering all three rounds
• Integration tests: End-to-end MPCv2 flow with real cryptographic operations
• Edge cases: Tests for unsupported share types and error handling
• Network mocking: Proper HTTP client testing with nock
• Backward compatibility: Tests ensure v1 generators still work

🔍 Technical Review

clientRoutes.ts (Lines 461-497)

const isMPCv2 = [
  ShareType.EddsaMPCv2Round1.toString(),
  ShareType.EddsaMPCv2Round2.toString(), 
  ShareType.EddsaMPCv2Round3.toString(),
].includes(req.decoded.sharetype) || req.decoded.sharetype.startsWith('EddsaMPCv2');

✅ Good: Robust MPCv2 detection with both enum matching and string prefix matching

External Signer Routing (Lines 924-951)

if (wallet._wallet.multisigTypeVersion === 'MPCv2') {
  return {
    ...req.body,
    customEddsaMPCv2SigningRound1GenerationFunction: createCustomEddsaMPCv2SigningRound1Generator(/*...*/),
    customEddsaMPCv2SigningRound2GenerationFunction: createCustomEddsaMPCv2SigningRound2Generator(/*...*/),
    customEddsaMPCv2SigningRound3GenerationFunction: createCustomEddsaMPCv2SigningRound3Generator(/*...*/),
  };
}

✅ Good: Clear separation between MPCv2 and v1 generator assignment

Generator Functions (Lines 1824-1867)

✅ Good: Identical structure to ECDSA MPCv2 generators with proper error handling and retry logic

📝 Minor Suggestions

1. Error Message Consistency

The EdDSA MPCv2 error message could match the ECDSA format:

// Current (line 480)
`Share type ${req.decoded.sharetype} not supported for EdDSA MPCv2, only EddsaMPCv2Round1, EddsaMPCv2Round2 and EddsaMPCv2Round3 is supported.`

// Suggested (matches ECDSA format on line 516)  
`Share type ${req.decoded.sharetype} not supported for EdDSA MPCv2, only EddsaMPCv2Round1, EddsaMPCv2Round2 and EddsaMPCv2Round3 are supported.`

2. Type Documentation Enhancement

The type definitions are excellent, but consider adding examples for better developer experience:

/**
 * @example
 * // EdDSA MPCv2 Round 1 request
 * POST /api/v2/tsol/tssshare/EddsaMPCv2Round1
 * {
 *   "txRequest": { "walletId": "...", "transactions": [...] }
 * }
 */

🚀 Recommendation: APPROVE

This is a high-quality implementation that:

• ✅ Meets all PR requirements (routes EddsaMPCv2Round1/2/3, adds generator factories, covers dispatch and signing-param wiring)
• ✅ Follows established patterns consistently
• ✅ Maintains backward compatibility
• ✅ Has comprehensive test coverage including edge cases
• ✅ Uses proper error handling and type safety
• ✅ Is production-ready with no security concerns identified

The implementation demonstrates solid understanding of the existing codebase architecture and cryptographic protocols. The minor suggestions above are optional enhancements that don't block approval.

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