feat(stellar): implement trustline validation with Redis cache (close…

[TheWeirdDee]

…s #36)

Before submitting a non-native Stellar asset payment, the payment service now validates that the recipient account holds a trustline for the asset. Validation results are cached in Redis for 60 seconds to avoid redundant Horizon round-trips on hot payment paths.

Changes:

• Add ERR_MISSING_TRUSTLINE error code mapped to HTTP 400
• Add meta field to AppError/errorHandler: always included in API responses (not stripped in production) so the changeTrustXdr is visible to clients
• Add MissingTrustlineError class (extends BusinessLogicError) carrying assetCode, assetIssuer, recipientAddress, and changeTrustXdr
• Add validateRecipientTrustline() in src/stellar/trustlineValidation.ts:
  • Skips check for native XLM
  • Resolves muxed (M-address) to base address before lookup
  • Redis cache key: trustline:validation:{address}:{code}:{issuer}, TTL 60 s
  • On cache miss: loads account from Horizon, checks balances
  • On missing trustline: builds unsigned ChangeTrust XDR for recipient to sign
  • Unfunded (404) accounts: fall back to dummy-sequence XDR template
• Replace ad-hoc trustline checks in stellarService.sendPayment() and payments.executePathPayment() with validateRecipientTrustline()
• Add localized ERR_MISSING_TRUSTLINE messages for en, fr, es, pt, sw
• Add 21 tests covering cache hit/miss, 404, Horizon errors, XDR correctness, error class shape, cache TTL and key format (35/35 tests passing)
• Fix pre-existing payments.test.ts issues: mock accounts were missing the Account interface methods (sequenceNumber, accountId) required by stellar-base 11, and the strictReceivePaths assertion had the wrong signature

Description

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Related Issue

Fixes #(issue number)

Type of Change

• Bug fix
• New feature
• Documentation update
• Code refactoring
• Performance improvement

Changes Made

Testing

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Checklist

• Code follows project style
• Self-reviewed my code
• Commented complex code
• Updated documentation
• No new warnings
• Added tests (if applicable)

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