fix(desktop): keep working-badge rows painted so the pulse animates smoothly

Closed thread ingress rows render inside .timeline-row-cv, which applies
content-visibility: auto. The browser may skip or throttle rendering work
for contained rows, so the badge's opacity pulse stuttered on the closed
timeline while the same activity animated smoothly in the open thread panel
(which has no containment) — exactly the reported repro signal.

Opt only rows with an active working badge out of containment via a
data-agent-working attribute on the row wrapper, mirroring the existing
:hover/:focus-within un-pause rule. Scope stays tight: at most the one or
two rows with live agent activity lose containment, and only while the
badge is showing.

Co-authored-by: Taylor Ho <taylorkmho@gmail.com>
Signed-off-by: Taylor Ho <taylorkmho@gmail.com>

desktop/src/features/messages/ui/TimelineMessageList.tsx

@@ -283,6 +283,13 @@ export const TimelineMessageList = React.memo(function TimelineMessageList({
           {group.items.map((item) => (
             <div
               className="timeline-row-cv"
+              data-agent-working={
+                item.kind === "message" &&
+                item.entry.summary != null &&
+                workingThreadHeadIds?.has(item.entry.message.id)
+                  ? "true"
+                  : undefined
+              }
               key={getTimelineItemKey(item)}
               style={timelineRowReserveStyle(item)}
             >

desktop/src/shared/styles/globals/utilities.css

@@ -22,6 +22,15 @@
     content-visibility: visible;
   }
 
+  /* Rows with an animated working badge must stay painted: under
+     content-visibility: auto the browser may skip/throttle rendering work for
+     off-screen or contained rows, which makes the badge pulse stutter on
+     closed thread ingress rows (the open-thread panel has no containment and
+     animates smoothly). Scoped to the 1-2 rows with active agent work. */
+  .timeline-row-cv[data-agent-working="true"] {
+    content-visibility: visible;
+  }
+
   .content-visibility-auto-interactive {
     content-visibility: auto;
     contain-intrinsic-size: auto 200px;