## Context This work item tracks the reinstatement of code changes that depend on the composite index `index_ssh_signatures_on_project_id_and_commit_sha` for the `ssh_signatures` table. The database index was already reintroduced in !216058, and this work item focuses on updating the application code to leverage the new index structure. ### Background The original merge request !214739 introduced changes to optimize SSH signature handling by restructuring database indexes on the `ssh_signatures` table. This was reverted in !215953 due to production incident #inc-6216, which caused 500 errors from SSH signature endpoints. ### Index changes (already ppplied) The composite index was reintroduced in !216058, which: * Dropped the `index_ssh_signatures_on_commit_sha` unique index * Dropped the redundant `index_ssh_signatures_on_project_id` index * Added two new composite unique indexes `index_ssh_signatures_on_project_id_and_commit_sha` and `index_ssh_signatures_on_commit_sha_and_project_id` This change is required for Cells to ensure that SSH signatures remain uniquely constrained by the combination of project and commit SHA, rather than commit SHA alone.