Worked on reliability improvements for domain unlock handling in user registration and deregistration flows within the kamailio/kamailio repository. Addressed a critical bug by fixing missing unlocks in the update_contacts function and correcting domain unlock logic in the IMS registrar, ensuring proper management of user deregistration. These targeted changes, implemented in C with a focus on network and system programming, resolved edge cases identified in issue #4553. The work stabilized domain state across the registration lifecycle, reducing potential service interruptions and improving uptime for large-scale deployments that depend on robust domain unlock handling in SIP infrastructure.