Remote Control app: file delivery via SendUserFile fails silently (red error triangle), tool reports success

When a Claude Code session sends a file to the user via the SendUserFile mechanism while the user is on the Remote Control mobile app, the file fails to open — shown as a red warning triangle on the file card — even though the tool call itself reports a successful send. This is reproducible (hit twice, ~1 month apart) and affects any file type. Workaround found: sending the same file via email attachment instead works reliably. Would appreciate this being looked at, since it silently breaks a documented capability (SendUserFile) specifically on the mobile Remote Control surface.

Start by reproducing the documented SendUserFile flow from a Claude Code session to the Remote Control mobile app, checking the file card and tool result. Compare it with the working email-attachment workaround; done means files of different types open successfully in the mobile app and failures are no longer reported as successful sends.

Written by the indexing model from the issue text.