# Regressions

One file per input that once found a bug. `tests/regressions.rs` replays every
file here through `shop_grid::oracle::check_bytes` on stable, so anything
landing in this directory is a permanent test by virtue of the directory, with
no test function to write and no chance of forgetting one.

- `2026-08-29-decstbm-inverted-region`: `ESC [ 20 ; 3 r`, an inverted DECSTBM
  region. Accepting one underflows `bottom - top + 1` in the scroll paths.
- `2026-08-29-delete-lines-whole-region`: `ESC [ 9999 M` with the cursor on
  the top row. DL clamps its count to the region size, and a copy loop that
  computes `scroll_bottom - n` underflows when the delete covers the whole
  region from its first row.
- `2026-08-29-pad-mistaken-for-half-a-pair`: a wide character with one column
  left leaves a pad at the right edge. Reading that pad as the second half of a
  pair makes a narrow write over it blank the cell two columns back, which is
  the spacer of a real pair, leaving its lead on screen as half a character.