The first T-197 fix flipped the wrong lever: it called
activateTab(Slots.workspace, 'editor.active'), but _WorkspaceSlot
renders its editor split off arrangement.editorOpen — not the active
tab — so clicking a file still showed nothing. Call arrangement
.openEditor() on editor.opened / active-changed(non-null), and
closeEditor() on active-changed(null) so the split collapses when the
last buffer closes. Test now asserts arrangement.editorOpen, the lever
the UI actually reads.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jpmschweitzerandClaude Opus 4.8
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