By: Michael Lynch <git@mtlynch.io>
Validate width in MediaFilename and add error case tests MediaFilename now rejects widths that have no corresponding stored file (e.g. 850px for video, or arbitrary widths for photos). Tests cover both the new error paths and the previously untested full-size variants. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>