Gate Cells claims verification behind attribute flag

What does this MR do and why?

Cells::Claims::VerificationService now respects the per-attribute rollout flag on cells_claims_attribute, so one flag gates both claiming and verification. Previously it only gated the live save path.

Three changes:

• Cells::Claimable#cells_claims_metadata skips any attribute where cells_claims_enabled_for_attribute? returns false.
• VerificationService gains a memoized enabled_claim_types helper, used for the claim_types: argument to ClaimService#list_records.
• VerificationService returns early, logging a warning, when no attribute of the model is enabled.

The metadata filter and the claim_types filter must ship together. Filtering metadata alone would leave remote claims unmatched locally, and diff_record would destroy them via missing_attribute_in_local.

The empty-case guard exists because an empty claim_types array means no filter in the protobuf request, not match-nothing. Without it, a fully disabled model would fetch and destroy every claim.

One attribute is affected today: ServiceDeskSetting#project_key_address_slug. Its flag, cells_claims_service_desk_settings_project_key_address_slugs, has never been enabled anywhere, but cells_claims_verification_worker_service_desk_setting has been enabled in production since 2026-03-27. Verification has therefore been claiming this attribute regardless of its flag. Claims already written are left in place, not destroyed.

References

• gitlab-com/gl-infra/tenant-scale/cells-infrastructure/team#737 (closed)

How to set up and validate locally

1. Set up cells in the GDK, per https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/cells.md#setting-up-cells-locally.
2. In rails console, run Feature.disable(:cells_claims_service_desk_settings_project_key_address_slugs), then confirm ServiceDeskSetting.where.not(project_key_address_slug: nil).first.cells_claims_metadata no longer includes that attribute.
3. Run Cells::Claims::VerificationService.new(ServiceDeskSetting, timeout: 1.minute).execute and confirm no new claim rows for that attribute via gdk psql -d topology_service -c "SELECT * FROM claims;".

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