Navigations keep the previous view rendering while scanning: target and
parent legs land as one two-pane frame when the parent leg settles within
a 200ms wait bound (past it the target lands alone and the late leg
upgrades in place; Escape inside the landing window withdraws the
navigation). The loading indicator floats over the content on the card
background and appears only once a scan outlives a 300ms silence window,
so navigation never shifts the columns or flashes an intermediate frame.
The truncated note now describes the on-screen panes instead of hiding
during scans.
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