The interactive environment picker rendered a bare SelectValue, so the
overflow measurement never saw it and it stayed full-width while its
neighbours collapsed. It now carries the same label marker and transition.

The Code row accepted any custom family, including proportional faces that
break column alignment in code blocks, diffs, and file previews. It requires
monospace now, matching Terminal.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>