The classic CLI status bar could appear twice after a horizontal terminal
resize — two bars at two widths with two different elapsed readings.
Root cause: prompt_toolkit's Application._on_resize() calls renderer.erase(),
which does cursor_up(_cursor_pos.y) + erase_down() using the _cursor_pos.y
cached from the LAST render at the OLD width (renderer.py:745). On a column
shrink the terminal reflows the already-painted full-width chrome into extra
physical rows, so the cached y undershoots: cursor_up doesn't climb past the
reflowed rows and erase_down leaves the old bar stranded ABOVE the live
origin. The next paint stacks a fresh bar below it. The existing post-resize
suppression hides the NEW bar for ~0.35s but never erases the already-reflowed
OLD one, so the ghost survives the whole window. Ctrl+L / /redraw clears it,
confirming a viewport wipe is the fix.
Fix: on a WIDTH change, _recover_after_resize now routes through the same
recovery as Ctrl+L — _clear_prompt_toolkit_screen(rebuild_scrollback=False)
(CSI 2J, visible viewport only) + _replay_output_history() — BEFORE delegating
to prompt_toolkit's resize. Banner-safe: 2J never touches scrollback history
(that's CSI 3J, which we don't send here), so the startup banner is preserved.
Rows-only resizes skip the clear (no reflow → no ghost) to avoid an extra
repaint. Tracks _last_resize_width to distinguish the two.
Tests: replace the now-obsolete 'never clears on resize' assertion with two
tests — rows-only resize delegates without clearing; width change clears the
viewport + replays and never wipes scrollback.
