In December 2025, Yasufumi Kiuchi enhanced the Aryakoste/mattermost repository by implementing support for full-width at-signs in the mentions textbox, addressing a common issue for multilingual users. He updated the mention detection logic by refining the regular expression and pretext handling to recognize both full-width and half-width at-signs, ensuring accurate user mentions regardless of character width. This feature, developed using React and tested with JavaScript and TypeScript, improved the user experience by reducing mention errors and aligning with accessibility standards. The work was delivered as a focused, single-commit change, demonstrating depth in front end development and thoughtful problem-solving.