Remove the approval_rules_finalize_shorter_transaction feature flag

Marc Shawrequested to merge
629136-remove-approval-rules-finalize-shorter-transaction-ff into master

What does this MR do and why?

Removes the approval_rules_finalize_shorter_transaction feature flag and keeps the behaviour it gated. ApprovalRules::FinalizeService now always reads CODEOWNERS before opening the finalize transaction and bulk inserts group approvers with one statement per rule. The flag reached 100% on GitLab.com on 2026-09-30 with no issues.

Detailed context for AI agents
  • Flag introduced in !255430 (merged) as part of #628868 (closed) (long MergeWorker transactions in ApprovalRules::FinalizeService).
  • Rollout: verified both halves on GitLab.com on 2026-09-30, then 10% → 25% → 100% the same day. No exceptions logged against the flag, no change on the MergeWorker dashboard.
  • Changes: the optimized_transaction? memoized predicate is deleted, the approvals_required_pre_merge pre-read runs unconditionally, and merge_group_members_into_users always calls insert_group_users instead of falling back to rule.users |= rule.group_users. The flag YAML and the two spec contexts for the flag-off path are removed.
  • The sibling flag approval_rules_finalize_bulk_copy_approvers (the copy_project_rules path) is intentionally left in place and has its own rollout.
  • Verified locally: ee/spec/services/approval_rules/finalize_service_spec.rb passes (14 examples). grep shows no remaining references to the flag name.

References

Screenshots or screen recordings

Not applicable, backend-only change.

How to set up and validate locally

  1. On an EE instance, create a project with an approval rule that includes a group, and a merge request that overrides approval rules.
  2. Merge the merge request.
  3. In the Rails console, confirm the group members were attached to the MR-level rule: 
    MergeRequest.last.approval_rules.regular.first.users

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