fix(front): stabilize artifact paths during streaming (#4094)

frontend/src/components/workspace/messages/message-list.tsx

@@ -691,6 +691,8 @@ export function MessageList({
     return <MessageListSkeleton />;
   }
 
+  const artifactPaths = extractArtifactsFromThread(thread);
+
   return (
     <>
       <Conversation
@@ -731,7 +733,7 @@ export function MessageList({
                           groupIndex === groupedMessages.length - 1
                         }
                         threadId={threadId}
-                        artifactPaths={extractArtifactsFromThread(thread)}
+                        artifactPaths={artifactPaths}
                         runId={
                           group.type === "assistant"
                             ? (msg as { run_id?: string }).run_id

frontend/src/core/artifacts/utils.ts

@@ -2,6 +2,8 @@ import { getBackendBaseURL } from "../config";
 import { isStaticWebsiteOnly } from "../static-mode";
 import type { AgentThreadState } from "../threads";
 
+const EMPTY_ARTIFACT_PATHS: readonly string[] = [];
+
 export function urlOfArtifact({
   filepath,
   threadId,
@@ -25,7 +27,7 @@ export function urlOfArtifact({
 export function extractArtifactsFromThread(thread: {
   values: Pick<AgentThreadState, "artifacts">;
 }) {
-  return thread.values.artifacts ?? [];
+  return thread.values.artifacts ?? EMPTY_ARTIFACT_PATHS;
 }
 
 export function resolveArtifactURL(absolutePath: string, threadId: string) {

frontend/tests/unit/core/artifacts/utils.test.ts

@@ -74,6 +74,19 @@ describe("artifact URL helpers", () => {
     ).toBe("/demo/threads/thread-1/user-data/outputs/style.css");
   });
 
+  test("returns stable artifact path references", async () => {
+    const { extractArtifactsFromThread } = await loadFreshArtifactUtils();
+    const threadWithoutArtifacts = { values: {} };
+    const artifacts = ["/mnt/user-data/outputs/chart.png"];
+
+    expect(extractArtifactsFromThread(threadWithoutArtifacts)).toBe(
+      extractArtifactsFromThread(threadWithoutArtifacts),
+    );
+    expect(extractArtifactsFromThread({ values: { artifacts } })).toBe(
+      artifacts,
+    );
+  });
+
   test("resolves a relative message image when it uniquely matches an artifact", async () => {
     const { resolveMessageImageURL } = await loadFreshArtifactUtils();
     const artifacts = [