fix(desktop): polish compaction indicator and preserve scrollback

Show a shimmering "Summarizing thread" label during auto-compaction, skip
the post-turn hydrate when compaction fired so the live transcript does not
collapse to the stored summary-only session.

apps/desktop/src/components/assistant-ui/thread.tsx

@@ -96,7 +96,7 @@ import { extractPreviewTargets } from '@/lib/preview-targets'
 import { useEnterAnimation } from '@/lib/use-enter-animation'
 import { cn } from '@/lib/utils'
 import { playSpeechText, stopVoicePlayback } from '@/lib/voice-playback'
-import { $compactionStatus } from '@/store/compaction'
+import { $compactionActive } from '@/store/compaction'
 import type { ComposerAttachment } from '@/store/composer'
 import { notifyError } from '@/store/notifications'
 import { $connection } from '@/store/session'
@@ -337,15 +337,25 @@ const StatusRow: FC<{ children: ReactNode; label: string } & React.ComponentProp
   </div>
 )
 
+// Fixed label while auto-compaction runs — decoupled from backend status text.
+const COMPACTION_LABEL = 'Summarizing thread'
+
+const CompactionHint: FC = () => (
+  <span className="shimmer min-w-0 truncate text-muted-foreground/55">{COMPACTION_LABEL}</span>
+)
+
 const ResponseLoadingIndicator: FC = () => {
   const { t } = useI18n()
   const elapsed = useElapsedSeconds()
-  const compaction = useStore($compactionStatus)
+  const compacting = useStore($compactionActive)
 
   return (
-    <StatusRow data-slot="aui_response-loading" label={compaction ?? t.assistant.thread.loadingResponse}>
+    <StatusRow
+      data-slot="aui_response-loading"
+      label={compacting ? COMPACTION_LABEL : t.assistant.thread.loadingResponse}
+    >
       <span aria-hidden="true" className="dither inline-block size-3 rounded-[2px] text-midground/80 animate-pulse" />
-      {compaction && <span className="min-w-0 truncate">{compaction}</span>}
+      {compacting && <CompactionHint />}
       <ActivityTimerText seconds={elapsed} />
     </StatusRow>
   )
@@ -380,7 +390,7 @@ const StreamStallIndicator: FC = () => {
   })
 
   const [stalled, setStalled] = useState(false)
-  const compaction = useStore($compactionStatus)
+  const compacting = useStore($compactionActive)
 
   useEffect(() => {
     setStalled(false)
@@ -389,8 +399,7 @@ const StreamStallIndicator: FC = () => {
     return () => window.clearTimeout(id)
   }, [activity])
 
-  // Compaction surfaces immediately; an ordinary stall waits out STREAM_STALL_S.
-  const active = stalled || Boolean(compaction)
+  const active = stalled || compacting
   const elapsed = useElapsedSeconds(active)
 
   if (!active) {
@@ -398,9 +407,13 @@ const StreamStallIndicator: FC = () => {
   }
 
   return (
-    <StatusRow className="mt-1.5" data-slot="aui_stream-stall" label={compaction ?? 'Hermes is thinking'}>
+    <StatusRow
+      className="mt-1.5"
+      data-slot="aui_stream-stall"
+      label={compacting ? COMPACTION_LABEL : 'Hermes is thinking'}
+    >
       <span aria-hidden="true" className="dither inline-block size-3 rounded-[2px] text-midground/80 animate-pulse" />
-      {compaction && <span className="min-w-0 truncate">{compaction}</span>}
+      {compacting && <CompactionHint />}
       <ActivityTimerText seconds={elapsed} />
     </StatusRow>
   )