fix(ui): show shimmer and icon on initial Working... state for new agent runs

Eliminates two visual glitches when a new agent run starts:
1. The initial "Working..." was rendered as plain text without the shimmer
   animation or agent icon — now matches the proper working state styling.
2. A brief blank flash occurred when transcript chunks arrived but hadn't
   produced parseable parts yet — fixed by deriving waitingText from parts
   availability instead of the hasOutput flag.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/components/IssueChatThread.tsx

@@ -818,7 +818,7 @@ function IssueChatAssistantMessage() {
   const runHref = runId && runAgentId ? `/agents/${runAgentId}/runs/${runId}` : null;
   const chainOfThoughtLabel = typeof custom.chainOfThoughtLabel === "string" ? custom.chainOfThoughtLabel : null;
   const hasCoT = message.content.some((p) => p.type === "reasoning" || p.type === "tool-call");
-  const isFoldable = !isRunning && hasCoT && !!chainOfThoughtLabel;
+  const isFoldable = !isRunning && !!chainOfThoughtLabel;
   const [folded, setFolded] = useState(isFoldable);
   const [prevFoldKey, setPrevFoldKey] = useState({ messageId: message.id, isFoldable });
 
@@ -900,8 +900,15 @@ function IssueChatAssistantMessage() {
                   }}
                 />
                 {message.content.length === 0 && waitingText ? (
-                  <div className="rounded-sm bg-accent/20 px-3 py-2 text-sm text-muted-foreground">
-                    {waitingText}
+                  <div className="flex items-center gap-2.5 rounded-lg px-1 py-2">
+                    <span className="inline-flex items-center gap-2 text-sm font-medium text-foreground/80">
+                      {agentIcon ? (
+                        <AgentIcon icon={agentIcon} className="h-4 w-4 shrink-0" />
+                      ) : (
+                        <Loader2 className="h-4 w-4 shrink-0 animate-spin text-muted-foreground" />
+                      )}
+                      <span className="shimmer-text">{waitingText}</span>
+                    </span>
                   </div>
                 ) : null}
                 {notices.length > 0 ? (

ui/src/lib/issue-chat-messages.ts

@@ -593,22 +593,17 @@ function normalizeLiveRuns(
 function createLiveRunMessage(args: {
   run: LiveRunForIssue;
   transcript: readonly IssueChatTranscriptEntry[];
-  hasOutput: boolean;
 }) {
-  const { run, transcript, hasOutput } = args;
+  const { run, transcript } = args;
   const { parts, notices, segments } = buildAssistantPartsFromTranscript(transcript);
   const waitingText =
     run.status === "queued"
       ? "Queued..."
-      : hasOutput
+      : parts.length > 0
         ? ""
         : "Working...";
 
-  const content = parts.length > 0
-    ? parts
-    : waitingText
-      ? [{ type: "text", text: waitingText } satisfies TextMessagePart]
-      : [];
+  const content = parts;
 
   const message: ThreadAssistantMessage = {
     id: `live-run:${run.id}`,
@@ -712,7 +707,6 @@ export function buildIssueChatMessages(args: {
       message: createLiveRunMessage({
         run,
         transcript: transcriptsByRunId?.get(run.id) ?? [],
-        hasOutput: hasOutputForRun?.(run.id) ?? false,
       }),
     });
   }