[ranjan1969x]

Summary

Adds comprehensive deterministic unit tests covering Stellar envelope validation and replay edge cases in parseAndValidateSignedEnvelope:

• Valid envelope parsing asserting correct signature count and source public key.
• Multi-signed envelope support with exact signature count verification.
• FeeBumpTransaction parsing asserting inner transaction source and inner signature count.
• Rejection of FeeBumpTransaction with unsigned inner transactions (HTTP 400).
• Boundary sequence numbers including zero sequence and high 64-bit integer sequences.
• Multi-network passphrase behavior and network configuration error propagation.
• Malformed XDR handling including non-base64 input, empty/whitespace strings, non-transaction valid XDR structures, and truncated transaction envelopes (HTTP 400).

Test Coverage

• npm test -- src/utils/__tests__/stellarEnvelope.test.ts: 12/12 tests passing 100% green.
• Full suite: 125 test suites passing, 1081 tests green.
• npm run build: 0 errors.
• npm run lint: 0 errors.

Closes #2088