T1: ChipShadow, a terminal's notice chips cast a cell's shadow

ChipShadow on|off (off; the tty shell's, §9.2 T1): each notice chip casts
a shadow one cell right and one down inside its own pane's body: on a
blank cell a half block (▌ right, ▀ below, ▘ at the corner) in a colour
35% darker than the ground (OKLab), so the shadow is half a cell thick;
under text the ground itself darkened. Never the cursor's cell, a
selection, a tag or another chip; truecolor terminals only.

Tests: the shadow lies right of or below the chip, never in it; nothing
with it off or without truecolor. Snapshots unchanged. Feel review:
.scratch/render/tty/shadow/.

1 files changed, 2 insertions, 0 deletions

diff --git a/docs/config.md b/docs/config.md
index 1d83bd8e..45677170 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -585,6 +585,8 @@ Afterglow on     text that changes glows for a moment in the theme's accent
 JumpTrail on     in a terminal, a jump of the cursor of three cells or more
                  leaves a trail of a few cells that fades in 120 ms
                  (truecolor terminals; a pixel shell glides instead)
+ChipShadow on    in a terminal, a notice chip casts a shadow a cell right and
+                 down: half blocks on blank cells, a darker ground on text
 CursorBlink on   the cursor blinks, solid while typing and half a second
                  after, eased at each edge, solid after 10 idle seconds
 GripWidth 150    the grip's button and the scrollbar under it, percent of the