Use an explicit runtime check to apply the newer corner styling on macOS 26 while leaving behavior unchanged on older macOS versions for compatibility.
Also add the required QuartzCore framework for linking the corner curve API.
screen_draw_overlay_line accessed self->linebuf->line->cpu_cells
without ever calling linebuf_init_line on the shared view. Render
paths that initialize a stack-local Line via render_line_for_virtual_y
left the view's cpu_cells as NULL (the value set by alloc_line via
PyType_GenericAlloc), and the multicell-trim loop then dereferenced
NULL + xstart * sizeof(CPUCell), producing a SIGSEGV at a small
address (e.g. 0x1e for xstart=2). The crash was reachable any time
an IME pre-edit overlay was rendered with the cursor not in column 0
on a screen whose linebuf->line had not been re-pointed by some
unrelated prior call.
Fix by initializing the view at the overlay row on entry. Add a
test_draw_overlay_line method on Screen so the behavior can be
exercised directly from a regression test.
When toggling between alt and main screen buffers, the selection buffer
(is_selected) was not always re-uploaded to the GPU. This caused a size
mismatch because render_lines_for_screen depends on pixel_scroll_enabled,
which depends on linebuf == main_linebuf.
On alt screen, pixel_scroll is disabled so render_lines = screen->lines.
On main screen, pixel_scroll is enabled so render_lines = screen->lines + 1.
After switching from alt to main, the cell data buffer was re-uploaded with
the larger size (is_dirty = true), but the selection buffer was not
(screen_is_selection_dirty could return false if no selections/urls/extra
cursors were active). The extra row of cells then read out-of-bounds from
the selection buffer, getting garbage data that the shader interpreted as
extra cursor shapes, producing blinking cursor-colored artifacts.
Fix by unconditionally setting extra_cursors.dirty = true after screen
toggle, ensuring the selection buffer is always re-uploaded with the
correct size matching the cell data buffer.
Agent-Logs-Url: https://github.com/kovidgoyal/kitty/sessions/daa73124-4795-4389-aea5-bb5593a26d9f
Co-authored-by: kovidgoyal <1308621+kovidgoyal@users.noreply.github.com>
