Steady the Working shimmer; instant archive slot

The Working marker mounts and unmounts with every gap between tool
executions; replaying its entrance fade on each reappearance read as
blinking instead of a shimmer. Drop the entrance animation on that row
and start the shimmer band mid-sweep (negative animation-delay) so even
short-lived mounts show the moving band rather than the transparent
lead-in.

The sidebar archive slot now appears instantly on hover instead of
animating its width.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

desktop/src/features/chats/ui/ChatActivityTranscript.tsx

@@ -608,7 +608,9 @@ function LiveTurnMarker({
           <span>Waiting for the first backend event…</span>
         )
       }
-      entrance={hasRecentEntrance(startedAt)}
+      // No entrance animation: this row mounts and unmounts with every gap
+      // between tool executions, and replaying the fade on each reappearance
+      // reads as blinking instead of a steady status.
       icon={icon}
       label="Working"
       loading

desktop/src/features/chats/ui/ChatListItem.tsx

@@ -108,8 +108,8 @@ export function ChatListItem({
       </button>
       {onArchiveChat ? (
         // Zero-width until hover/focus so the title gets the full row; the
-        // slot expands to make room for the archive button on demand.
-        <div className="relative flex h-6 w-0 shrink-0 items-center justify-center overflow-hidden transition-[width] duration-150 group-focus-within/chat-row:w-6 group-hover/chat-row:w-6">
+        // slot appears instantly to make room for the archive button.
+        <div className="relative flex h-6 w-0 shrink-0 items-center justify-center overflow-hidden group-focus-within/chat-row:w-6 group-hover/chat-row:w-6">
           <Button
             aria-label={`Archive ${name}`}
             className={cn(

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

@@ -165,6 +165,10 @@
 .buzz-shimmer::before,
 .shimmer::before {
   animation: buzz-shimmer var(--buzz-shimmer-duration) linear infinite;
+  /* Start mid-sweep so freshly mounted rows (the Working marker re-mounts
+     between tool executions) show the band immediately instead of waiting
+     out the transparent lead-in. */
+  animation-delay: calc(var(--buzz-shimmer-duration) / -2);
   background-clip: text;
   background-image: linear-gradient(
     90deg,