sl0ppty: a pane that rings says so

libghostty-vt already had a BEL effect; nothing was listening. A pane now marks
its titlebar when one arrives, and stays marked until the pane is looked at.

It marks the *tab* as well, which is the half that makes it useful. A bell
exists for the pane you are not watching, and a mark that only appeared on
screen would be missing precisely when the pane is in a background tab — which
is where an agent finishing a job, or a build wanting input, actually happens.

Looking at a pane is the acknowledgement, and it is done once per frame before
anything is drawn rather than while the pane itself is painted. The tab strip is
drawn first, so clearing during the pane's own paint left the strip reporting a
bell that had already been answered for one frame — visible as a stale dot that
went away on the next unrelated repaint. Doing it up front also means every
route to "this pane is focused" clears it, not only the routes that thought to.

The mark is a configurable string rather than a fixed glyph. The obvious choice
is an emoji bell, emoji are drawn two columns wide by many terminals, and
screen_text books every chrome cell as one — so the default is a narrow bullet
and anyone who knows their own terminal can say otherwise. config.kdl has no \\u
escape, so it holds the character itself; that cost a round trip to notice.

bell_indicator false makes a bell silent and invisible, which is a real choice
and not an oversight, so it is spelled out in the config.

1 files changed, 16 insertions, 0 deletions

diff --git a/config/config.kdl b/config/config.kdl
index 70b1a8a..7a68933 100644
--- a/config/config.kdl
+++ b/config/config.kdl
@@ -29,6 +29,22 @@ title_align "center"
 // of this, so it can never end up welded to the rule beside it.
 title_inset 2
 
+// ── the bell ────────────────────────────────────────────────────────────────
+//
+// A BEL from a program marks the pane it came from, and the tab that pane is
+// in -- a bell exists for the pane you are *not* looking at, and one that only
+// showed on screen would be useless in a background tab. Looking at the pane
+// is what puts it out. Off makes a bell silent *and* invisible, which is a
+// real choice rather than an oversight.
+bell_indicator true
+
+// What to draw. A short string rather than a fixed glyph, because the obvious
+// choice is an emoji bell and emoji are drawn two columns wide by many
+// terminals while chrome here is booked as one -- so the default is narrow and
+// anyone who knows their own terminal can say otherwise. (This file has no
+// \u escape, so put the character itself here.)
+bell_mark "•"
+
 // The one-row bar with tabs, the +tab button and the pane count.
 status_bar true