When a single source is selected, every row in the middle sidebar repeats
that same source, so the source column is pure waste — the pane header
already names the source. The column now only shows under "All sources"
(where it's needed to tell rows apart); selecting a source hides it and
gives the width back to the artifact title. Also drops the now-dangling
row-main border-right in that state.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
peter
fbc4b7249b