fix: auto-complete previous pending messages when a new assistant message starts

When the agent produces multiple intermediate responses during a turn,
each gets a unique messageId but all stay pending until finalizeTurn().
This caused multiple stacked 'Thinking' bubbles in the chat transcript.

Now, when a new messageId arrives in applyTurnDelta, any previously
pending assistant messages are marked complete and message-complete
events are emitted before the new message-delta. The renderer reducer
mirrors this logic for defensive consistency.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/main/AryxAppService.ts

@@ -1471,11 +1471,20 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
         ? mergeStreamingText(existing.content, event.contentDelta)
         : (event.content ?? event.contentDelta);
 
+    // When a new assistant message begins, auto-complete any previously pending
+    // assistant messages so only the latest one shows the "Thinking" indicator.
+    const completedMessages: ChatMessageRecord[] = [];
     if (existing) {
       existing.content = content;
       existing.pending = true;
       existing.authorName = event.authorName;
     } else {
+      for (const message of session.messages) {
+        if (message.pending && message.role === 'assistant') {
+          message.pending = false;
+          completedMessages.push(message);
+        }
+      }
       session.messages.push({
         id: event.messageId,
         role: 'assistant',
@@ -1498,6 +1507,16 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
     session.updatedAt = occurredAt;
     await this.workspaceRepository.save(workspace);
 
+    for (const completed of completedMessages) {
+      this.emitSessionEvent({
+        sessionId,
+        kind: 'message-complete',
+        occurredAt,
+        messageId: completed.id,
+        authorName: completed.authorName,
+        content: completed.content,
+      });
+    }
     this.emitSessionEvent({
       sessionId,
       kind: 'message-delta',

src/renderer/lib/sessionWorkspace.ts

@@ -112,10 +112,18 @@ function applyMessageDeltaEvent(session: SessionRecord, event: SessionEventRecor
     };
   }
 
+  // Auto-complete any previously pending assistant messages so only
+  // the new message shows the "Thinking" indicator.
+  const completedMessages = session.messages.map((message) =>
+    message.pending && message.role === 'assistant'
+      ? { ...message, pending: false }
+      : message,
+  );
+
   return {
     ...session,
     messages: [
-      ...session.messages,
+      ...completedMessages,
         {
           id: event.messageId,
           role: 'assistant',

tests/renderer/sessionWorkspace.test.ts

@@ -228,6 +228,46 @@ describe('session workspace helpers', () => {
     expect(updated?.sessions[0].runs).toEqual([run]);
   });
 
+  test('auto-completes previous pending assistant messages when a new message starts', () => {
+    const first = applySessionEventWorkspace(createWorkspace(), {
+      sessionId: 'session-1',
+      kind: 'message-delta',
+      occurredAt: '2026-03-23T00:00:01.000Z',
+      messageId: 'assistant-1',
+      authorName: 'Primary Agent',
+      contentDelta: 'Exploring the codebase...',
+      content: 'Exploring the codebase...',
+    } satisfies SessionEventRecord);
+
+    expect(first?.sessions[0].messages).toHaveLength(1);
+    expect(first?.sessions[0].messages[0]).toMatchObject({
+      id: 'assistant-1',
+      pending: true,
+    });
+
+    const second = applySessionEventWorkspace(first, {
+      sessionId: 'session-1',
+      kind: 'message-delta',
+      occurredAt: '2026-03-23T00:00:02.000Z',
+      messageId: 'assistant-2',
+      authorName: 'Primary Agent',
+      contentDelta: 'Still exploring...',
+      content: 'Still exploring...',
+    } satisfies SessionEventRecord);
+
+    expect(second?.sessions[0].messages).toHaveLength(2);
+    expect(second?.sessions[0].messages[0]).toMatchObject({
+      id: 'assistant-1',
+      content: 'Exploring the codebase...',
+      pending: false,
+    });
+    expect(second?.sessions[0].messages[1]).toMatchObject({
+      id: 'assistant-2',
+      content: 'Still exploring...',
+      pending: true,
+    });
+  });
+
   test('ignores events for unknown sessions', () => {
     const workspace = createWorkspace();
     expect(