Codex review on #1599: the blank-viewport guard must compare the new transcript length against the viewport top used by the padded repaint, not #scrollbackHighWater. Prior unknown-POSIX viewport repaints can commit a long logical frame without advancing the high-water mark, so the stale high-water mark still lets all-blank deferred shrinks through.\n\nCompute paddedViewportTop from #previousLines.length - height and rebuild when the new tail cannot reach it. Add a regression for an offscreen POSIX viewport repaint that grows the committed frame to 120 rows while high-water remains at the original 20-row overflow, then shrinks to 15 rows.
roboomp
a882e9744b