The per-step paint toggled the row you arrived at, so going down then
back up toggled off the rows re-entered but never the furthest row you
turned around on — it stayed marked. Anchor the selection instead: on
entering visual mode record the anchor row, and on each move reconcile
marks to the contiguous range [anchor, cursor], toggling only the rows
whose membership changed. Moving back now cleanly reverses; jumps
reconcile the whole span. visual state becomes Option<usize> (the
anchor). Adds a regression test (down then fully up leaves only the
anchor); 90 cbd-tui tests green, clippy/fmt clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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