Tell me about a time when you dealt with buggy code in production that couldn't be fixed with a rollback.

In a previous role, we encountered a critical bug in production that impacted user data integrity. A standard rollback wasn't feasible due to the nature of the change, which involved a complex data migration that had already modified a significant portion of our user base. Instead of rolling back, we immediately spun up a hotfix branch. We meticulously analyzed the root cause in a staging environment that mirrored production as closely as possible. The fix involved a targeted script to correct the corrupted data and a patch to prevent the bug from recurring. We thoroughly tested the fix in staging, deployed it to production during a low-traffic window, and closely monitored system performance and data integrity. The issue was resolved within a few hours without data loss or further disruption.