- Treat same-dimension resize events in alt-screen mode as a repaint
signal, because terminal hosts can reflow or restore the physical
buffer without changing columns/rows.
- Ensure pending resize erases are emitted even when the virtual diff
is empty, so stale physical glyphs are still cleared.
- Extract alt-screen resize repaint into prepareAltScreenResizeRepaint()
for readability.
- Add defensive clearTimeout in prepareAltScreenResizeRepaint so rapid
resize bursts don't stack redundant delayed repaints.
- Add a focused regression test for same-dimension alt-screen resize
healing.
Addresses #18449
Related to #17961
4813aaf0ba