fix: stabilize streamed message rendering

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

sidecar/src/Eryx.AgentHost/Contracts/ProtocolModels.cs

@@ -167,6 +167,7 @@ public sealed class TurnDeltaEventDto : SidecarEventDto
     public string MessageId { get; init; } = string.Empty;
     public string AuthorName { get; init; } = string.Empty;
     public string ContentDelta { get; init; } = string.Empty;
+    public string? Content { get; init; }
 }
 
 public sealed class TurnCompleteEventDto : SidecarEventDto

sidecar/src/Eryx.AgentHost/Services/CopilotWorkflowRunner.cs

@@ -119,6 +119,7 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
                 string messageId = update.Update.MessageId ?? $"{command.RequestId}-delta-{fallbackMessageIndex++}";
                 StreamingSegment segment = GetOrCreateSegment(segments, messageId, authorName);
                 segment.SetContent(StreamingTextMerger.Merge(segment.Content.ToString(), update.Update.Text));
+                segment.SetAuthorName(authorName);
 
                 await onDelta(new TurnDeltaEventDto
                 {
@@ -128,6 +129,7 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
                     MessageId = messageId,
                     AuthorName = authorName,
                     ContentDelta = update.Update.Text,
+                    Content = segment.Content.ToString(),
                 }).ConfigureAwait(false);
             }
             else if (evt is ExecutorCompletedEvent completed
@@ -477,7 +479,7 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
 
         public string MessageId { get; }
 
-        public string AuthorName { get; }
+        public string AuthorName { get; private set; }
 
         public StringBuilder Content { get; } = new();
 
@@ -486,6 +488,11 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
             Content.Clear();
             Content.Append(value);
         }
+
+        public void SetAuthorName(string value)
+        {
+            AuthorName = value;
+        }
     }
 
     private sealed class AgentBundle : IAsyncDisposable

sidecar/tests/Eryx.AgentHost.Tests/SidecarProtocolHostTests.cs

@@ -128,6 +128,7 @@ public sealed class SidecarProtocolHostTests
                     MessageId = "assistant-1",
                     AuthorName = "Primary",
                     ContentDelta = "Hello",
+                    Content = "Hello",
                 });
 
                 await onActivity(new AgentActivityEventDto
@@ -201,6 +202,7 @@ public sealed class SidecarProtocolHostTests
             {
                 Assert.Equal("turn-delta", deltaEvent.GetProperty("type").GetString());
                 Assert.Equal("Hello", deltaEvent.GetProperty("contentDelta").GetString());
+                Assert.Equal("Hello", deltaEvent.GetProperty("content").GetString());
             },
             toolEvent =>
             {

src/main/EryxAppService.ts

@@ -609,18 +609,24 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
     sessionId: string,
     event: TurnDeltaEvent,
   ): Promise<void> {
+    if (event.content === undefined && event.contentDelta === undefined) {
+      return;
+    }
+
     const session = this.requireSession(workspace, sessionId);
     const existing = session.messages.find((message) => message.id === event.messageId);
 
     if (existing) {
-      existing.content = mergeStreamingText(existing.content, event.contentDelta);
+      existing.content =
+        event.content ?? mergeStreamingText(existing.content, event.contentDelta);
       existing.pending = true;
+      existing.authorName = event.authorName;
     } else {
       session.messages.push({
         id: event.messageId,
         role: 'assistant',
         authorName: event.authorName,
-        content: event.contentDelta,
+        content: event.content ?? event.contentDelta,
         createdAt: nowIso(),
         pending: true,
       });
@@ -636,6 +642,7 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
       messageId: event.messageId,
       authorName: event.authorName,
       contentDelta: event.contentDelta,
+      content: event.content,
     });
   }
 
@@ -697,6 +704,7 @@ export class EryxAppService extends EventEmitter<AppServiceEvents> {
         occurredAt: nowIso(),
         messageId: message.id,
         authorName: message.authorName,
+        content: message.content,
       });
 
       this.emitCompletedActivity(sessionId, pattern, message);

src/renderer/components/ChatPane.tsx

@@ -418,7 +418,13 @@ export function ChatPane({
                               : `rounded-xl border px-4 py-3 text-[14px] leading-relaxed text-zinc-200 ${assistantContainerClass}`
                           }
                         >
-                          <MarkdownContent content={message.content} />
+                          {!isUser && message.pending ? (
+                            <div className="whitespace-pre-wrap break-words text-[14px] leading-relaxed text-zinc-200">
+                              {message.content}
+                            </div>
+                          ) : (
+                            <MarkdownContent content={message.content} />
+                          )}
                           {message.pending && message.content && (
                             <span className="mt-1 inline-block h-4 w-[2px] animate-pulse rounded-sm bg-zinc-400" />
                           )}

src/renderer/lib/sessionWorkspace.ts

@@ -77,17 +77,18 @@ function applyErrorEvent(session: SessionRecord, event: SessionEventRecord): Ses
 }
 
 function applyMessageDeltaEvent(session: SessionRecord, event: SessionEventRecord): SessionRecord {
-  if (!event.messageId || event.contentDelta === undefined) {
+  if (!event.messageId || (event.content === undefined && event.contentDelta === undefined)) {
     return session;
   }
 
+  const resolvedContent = event.content ?? event.contentDelta ?? '';
   const messageIndex = session.messages.findIndex((message) => message.id === event.messageId);
   if (messageIndex >= 0) {
     const existing = session.messages[messageIndex];
     const nextMessage: ChatMessageRecord = {
       ...existing,
       authorName: event.authorName ?? existing.authorName,
-      content: mergeStreamingText(existing.content, event.contentDelta),
+      content: event.content ?? mergeStreamingText(existing.content, resolvedContent),
       pending: true,
     };
 
@@ -112,14 +113,14 @@ function applyMessageDeltaEvent(session: SessionRecord, event: SessionEventRecor
     ...session,
     messages: [
       ...session.messages,
-      {
-        id: event.messageId,
-        role: 'assistant',
-        authorName: event.authorName ?? 'assistant',
-        content: event.contentDelta,
-        createdAt: event.occurredAt,
-        pending: true,
-      },
+        {
+          id: event.messageId,
+          role: 'assistant',
+          authorName: event.authorName ?? 'assistant',
+          content: resolvedContent,
+          createdAt: event.occurredAt,
+          pending: true,
+        },
     ],
     updatedAt: event.occurredAt,
   };
@@ -139,10 +140,15 @@ function applyMessageCompleteEvent(session: SessionRecord, event: SessionEventRe
   const nextMessage: ChatMessageRecord = {
     ...existing,
     authorName: event.authorName ?? existing.authorName,
+    content: event.content ?? existing.content,
     pending: false,
   };
 
-  if (nextMessage.authorName === existing.authorName && !existing.pending) {
+  if (
+    nextMessage.authorName === existing.authorName
+    && nextMessage.content === existing.content
+    && !existing.pending
+  ) {
     return session;
   }
 

src/shared/contracts/sidecar.ts

@@ -133,6 +133,7 @@ export interface TurnDeltaEvent {
   messageId: string;
   authorName: string;
   contentDelta: string;
+  content?: string;
 }
 
 export interface TurnCompleteEvent {

src/shared/domain/event.ts

@@ -15,6 +15,7 @@ export interface SessionEventRecord {
   messageId?: string;
   authorName?: string;
   contentDelta?: string;
+  content?: string;
   activityType?: SessionActivityType;
   agentId?: string;
   agentName?: string;

tests/renderer/sessionWorkspace.test.ts

@@ -36,6 +36,7 @@ describe('session workspace helpers', () => {
       messageId: 'assistant-1',
       authorName: 'Architect',
       contentDelta: 'Hello',
+      content: 'Hello',
     } satisfies SessionEventRecord);
 
     expect(created?.sessions[0].messages).toEqual([
@@ -56,6 +57,7 @@ describe('session workspace helpers', () => {
       messageId: 'assistant-1',
       authorName: 'Architect',
       contentDelta: ' world',
+      content: 'Hello world',
     } satisfies SessionEventRecord);
 
     expect(appended?.sessions[0].messages[0]).toMatchObject({
@@ -73,6 +75,7 @@ describe('session workspace helpers', () => {
       messageId: 'assistant-1',
       authorName: 'Implementer',
       contentDelta: 'Done',
+      content: 'Done',
     } satisfies SessionEventRecord);
 
     const completed = applySessionEventWorkspace(workspace, {
@@ -81,6 +84,7 @@ describe('session workspace helpers', () => {
       occurredAt: '2026-03-23T00:00:02.000Z',
       messageId: 'assistant-1',
       authorName: 'Implementer',
+      content: 'Done',
     } satisfies SessionEventRecord);
 
     expect(completed?.sessions[0].messages[0]).toMatchObject({
@@ -98,6 +102,7 @@ describe('session workspace helpers', () => {
       messageId: 'assistant-1',
       authorName: 'Writer',
       contentDelta: 'How about',
+      content: 'How about',
     } satisfies SessionEventRecord);
 
     const second = applySessionEventWorkspace(first, {
@@ -107,6 +112,7 @@ describe('session workspace helpers', () => {
       messageId: 'assistant-1',
       authorName: 'Writer',
       contentDelta: 'The **Ashen Crown** feels',
+      content: 'How about The **Ashen Crown** feels',
     } satisfies SessionEventRecord);
 
     const third = applySessionEventWorkspace(second, {
@@ -116,6 +122,7 @@ describe('session workspace helpers', () => {
       messageId: 'assistant-1',
       authorName: 'Writer',
       contentDelta: 'classic and timeless.',
+      content: 'How about The **Ashen Crown** feels classic and timeless.',
     } satisfies SessionEventRecord);
 
     expect(third?.sessions[0].messages[0]).toMatchObject({
@@ -125,6 +132,33 @@ describe('session workspace helpers', () => {
     });
   });
 
+  test('applies final content from completion events without waiting for a workspace refresh', () => {
+    const workspace = applySessionEventWorkspace(createWorkspace(), {
+      sessionId: 'session-1',
+      kind: 'message-delta',
+      occurredAt: '2026-03-23T00:00:01.000Z',
+      messageId: 'assistant-1',
+      authorName: 'Reviewer',
+      contentDelta: 'Draft',
+      content: 'Draft',
+    } satisfies SessionEventRecord);
+
+    const completed = applySessionEventWorkspace(workspace, {
+      sessionId: 'session-1',
+      kind: 'message-complete',
+      occurredAt: '2026-03-23T00:00:02.000Z',
+      messageId: 'assistant-1',
+      authorName: 'Reviewer',
+      content: 'Draft polished into the final review.',
+    } satisfies SessionEventRecord);
+
+    expect(completed?.sessions[0].messages[0]).toMatchObject({
+      authorName: 'Reviewer',
+      content: 'Draft polished into the final review.',
+      pending: false,
+    });
+  });
+
   test('updates session status and error state from session events', () => {
     const running = applySessionEventWorkspace(createWorkspace(), {
       sessionId: 'session-1',