#25975 (salvaging #24403) clamped decorative scrollback Panels and
streaming box rules to `max(32, min(width, 56))` as a defense against
terminal-emulator reflow when columns shrink. On any modern wide
terminal this made the response/reasoning borders look stubby — 56
cols inside a 200-col viewport.
#26137 (salvaging #25981, by @OutThisLife) landed a more fundamental
fix: prompt_toolkit's `_output_screen_diff` is monkey-patched so its
reserve-vertical-space cursor move no longer pushes chrome into
scrollback at all. With that in place, the clamp is no longer
load-bearing for the chrome-into-scrollback class of bugs — the
remaining risk is purely cosmetic reflow of *already stamped*
Panel borders during an aggressive column shrink, which we now
accept as a tradeoff for restoring proper full-width rendering.
Changes:
- `_scrollback_box_width()` returns `max(32, width)` (just the floor,
no upper cap). All 10 call sites stay valid.
- Updated `test_scrollback_box_width_caps_to_resize_safe_value` to
the new `test_scrollback_box_width_returns_viewport_width` asserting
full-width passthrough above the 32-col floor.
Floor of 32 is kept so `'─' * (w - 2)` math stays positive on tiny
terminals.
Refs #18449#19280#22976 (the original reflow class) and #25975
(the clamp this reverts).
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