During February 2025, Das J focused on backend stability for the go-vikunja/vikunja repository, addressing a critical issue in CalDAV integration. They implemented a targeted bug fix in Go to ensure the API correctly returns a 404 Not Found when a referenced project does not exist, replacing the previous 500 error. This adjustment improved error handling and API semantics, preventing cache corruption and unexpected behavior in CalDAV clients such as DavX5. By aligning the API’s response codes with resource existence, Das J enhanced interoperability and reliability for client applications, demonstrating depth in API development and backend engineering within a short timeframe.