Worked on the esphome/esphome repository to address a critical issue in Windows client certificate handling, focusing on the MQTT workflow. Delivered a targeted bug fix that resolved permission-denied errors by ensuring temporary certificate files were created with secure, Windows-appropriate permissions and reliably cleaned up after use. This approach reduced the risk of certificate leakage and improved the overall security and reliability of certificate processing for Windows users. The work demonstrated proficiency in Python, backend development, and cross-platform file management, resulting in a smoother build process and fewer support incidents related to certificate permissions in the ESPHome project.