🤖 Claude Code Review

Status: Complete

Summary

This PR fixes a critical security vulnerability by ensuring duplicate transaction detection works across the entire blockchain history, not just a limited depth window. The change is correct and necessary.

Security Context:
The previous implementation only checked retention*2 blocks (~576 blocks with default settings) when detecting if a transaction was already mined on the chain. An attacker could exploit this by including duplicate transactions that were mined outside this window, which Bitcoin consensus rules prohibit.

Changes:

• BlockValidation.go:854: Changed depth limit from retention*2 to math.MaxUint64 for full chain checking
• Added comprehensive test case covering this scenario

Analysis

✅ Implementation is correct:

• The SQL implementation (GetBlockHeaderIDs.go:110-114) already has safeguards against excessive memory allocation, capping pre-allocation at 10K entries regardless of the requested depth
• The recursive CTE query uses LIMIT $2 to constrain results, preventing runaway queries
• Response caching minimizes performance impact for repeated queries

✅ Test coverage is appropriate:

• The new test simulates a transaction mined at block 1000 being duplicated in block 1600
• Verifies the error message includes the conflicting block ID
• Properly tests the security fix beyond the old retention window

No issues found - this is a well-designed security fix with proper safeguards already in place.