T7: the scroll thumb flashes as a terminal pane scrolls

ThumbFlash (off by default) brightens a body's scroll thumb toward the ink
when its view moves and fades it back over 250 ms, truecolor only. The tty
present path now clears shell_continuous once before its effects and each
effect only raises it, so the trail and the flash no longer mask each other.

1 files changed, 2 insertions, 0 deletions

diff --git a/docs/config.md b/docs/config.md
index 45677170..8b995e8a 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -587,6 +587,8 @@ JumpTrail on     in a terminal, a jump of the cursor of three cells or more
                  (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
+ThumbFlash on    in a terminal, a pane's scroll thumb brightens as it scrolls
+                 and fades back over 250 ms
 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