Draft: Finding UUID Migration Phase 4: Transition GitLab to use new_uuid

What does this MR do and why?

Implements Phase 4 of the Finding UUID migration (#587800).

This is a draft/placeholder MR that will be expanded to include the full transition from uuid to new_uuid.

Scope of Work

The full transition requires updating:

Model Layer

• Update associations in Vulnerabilities::Finding using uuid as primary_key
• Update Vulnerabilities::Feedback (uses finding_uuid)
• Update Security::Finding (uses uuid as foreign key)
• Update Security::FindingEnrichment (uses finding_uuid)
• Update scopes: by_uuid, excluding_uuids

GraphQL

• Update mutations accepting uuid argument:
  • Security::Finding::SeverityOverride
  • Security::Finding::CreateJiraIssueFormUrl
  • Security::Finding::CreateExternalIssueLink
  • Security::Finding::CreateVulnerability
  • Security::Finding::CreateMergeRequest
  • Security::Finding::Dismiss
  • Security::Finding::CreateIssue
  • Security::Finding::RevertToDetected
• Update GraphQL types exposing uuid
• Update resolvers using uuid

Serializers & API

• Update Vulnerabilities::FindingEntity
• Update Vulnerabilities::FeedbackEntity
• Update REST API endpoints

Services & Finders

• Update ingestion services
• Update dismissal services
• Update finders using uuid

Feature Flag

The use_new_uuid_for_findings feature flag enables incremental rollout:

if Feature.enabled?(:use_new_uuid_for_findings, project)
  finding.new_uuid
else
  finding.uuid
end

Dependencies

This MR targets the Phase 3 branch and cannot be merged until:

• Phase 1 (!220835 (merged)) merges
• Phase 2 (!220866) merges
• Phase 3 (!220869) merges

Migration Plan

Phase	Issue	MR	Status
1	#587625 (closed)	!220835 (merged)	In Review
2	#587798	!220866	Pipeline Running
3	#587799	!220869	Pipeline Running
4	#587800	This MR	Draft
5	#587801	-	Not Started

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist.

Relates to #587800