Save, Save As and Save a Copy already added the save format's extension to a
name typed in the save panel, but every other write through it (Export,
Export Selection, Save as PDF, text and preset exports, Document Info) wrote
the name as typed, so "art" became an extensionless file.
The save panel's answer now goes through one rule (io::with_extension): kept
when it ends in the suggested name's extension or names a known format, else
that extension is added. The web already downloads under the suggested name
or adds the format's extension in its Save As dialog.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
9c707b37fc