With gui.sidePanels, a panel's gocui window is named after its first
tab, so when branches is grouped behind, say, worktrees, there is no
window called "branches" at all. The transient contexts
(remoteBranches, subCommits, commitFiles) initially point at the
windows "branches" and "commits", and layout() showed their views
whenever the window-to-view map named them as their window's current
view — without checking that the window exists in the layout. Since
the map is seeded from the contexts themselves, a window that no
panel owns keeps naming a transient view as its current view, and
that view had just been parked at full screen size (the fallback for
views in unlaid-out windows), so it covered every side panel below it
in z-order.
Only show a transient view if its window actually received dimensions
in this layout.
Fixes#5823.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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