Implement Unique Constraint for Transaction Evidence Identifier

[sbsmith09]

Implement Unique Constraint for Transaction Evidence Identifier

Original Task

Design Transaction Evidence Uniqueness Schema

Summary of Changes

Added database migration to enforce uniqueness of transaction evidence identifiers to prevent duplicate entries

Acceptance Criteria

Create a new database migration file for the uniqueness tracking schema
Add a unique constraint on evidence identifier column
Verify that attempting to insert a duplicate evidence record raises a database-level constraint violation
100% branch coverage for database schema changes
Performance overhead of uniqueness check is less than 10ms

Tests

• Verify unique constraint prevents duplicate evidence entries
• Measure performance impact of uniqueness check
• Validate that constraint violation occurs when attempting to insert duplicate evidence
• Confirm 100% branch coverage for schema migration