Investigate missing pool repository links

Background

This is a follow-up from Follow up on the missing pool repository after archving incident.

Objective

Investigate why pool repository links are missing in the database while the repositories still exist on disk.

Tasks

• Investigate why the rails db and disk would be out of sync. What causes the missing link between forks and pool repository.
• Determine if the missing link issue happens only to old projects
• Currently GitLab only checks the DB record if the pool repository is used by other projects. Explore potential ways to bypass this check on GitLab or Gitaly
• Document findings and propose solutions

Expected outcome

A clear understanding of why links are missing and recommendations for preventing pool repository deletion when they're still in use.

Sources:

1. Follow up on the missing pool repository after archving incident
2. The issue
3. Related issue
4. Related MR <<- this might explain why the link was broken.