Finding UUID Migration Phase 4: Transition GitLab to use new_uuid

Problem

After new_uuid is fully populated and has a NOT NULL constraint, we need to transition all GitLab code to use new_uuid instead of the old uuid column for findings.

Implementation

1. Audit all code paths that reference vulnerability_occurrences.uuid
2. Update code to read from new_uuid instead of uuid
3. Update any indexes, foreign keys, or constraints that reference uuid
4. Feature flag the transition for safe rollout
5. Update API responses and GraphQL schemas as needed
6. Ensure backward compatibility during transition period

Acceptance Criteria

• All code paths updated to use new_uuid
• Feature flagged for safe rollout
• API/GraphQL compatibility maintained
• No regressions in functionality

Dependencies

• Blocked by Phase 3 (NOT NULL constraint must be in place)

Related

• Part of Finding UUID migration series
• #587625 (closed) - Phase 1: Start populating new_uuid