fix(webapp): treat a transcript re-read that isn't a list as a failed read

Author: kathiekiwi

apps/webapp/app/components/dashboard-agent/settled-transcript.test.ts

@@ -1,7 +1,8 @@
 import { VIEW_BLOCK_VERSION } from "@internal/dashboard-agent-contracts";
-import { describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { liveProgress } from "./progress-line";
 import {
+  fetchChatTranscript,
   hasOpenInvestigation,
   mergeSettledMessages,
   pollSettledTranscript,
@@ -73,6 +74,51 @@ describe("merging a re-read transcript", () => {
   });
 });
 
+describe("reading the transcript endpoint", () => {
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  function respondWith(body: unknown, ok = true) {
+    vi.stubGlobal("fetch", async () => ({ ok, json: async () => body }) as unknown as Response);
+  }
+
+  it("returns the transcript when the response carries one", async () => {
+    respondWith({ messages: [OPEN, SETTLED] });
+    const fetched = await fetchChatTranscript<typeof OPEN>("/agent/transcript", "chat_1");
+    expect(fetched?.map((message) => message.id)).toEqual([OPEN.id, SETTLED.id]);
+  });
+
+  it("reads a response with no messages at all as a failed re-read", async () => {
+    respondWith({});
+    expect(await fetchChatTranscript("/agent/transcript", "chat_1")).toBeNull();
+  });
+
+  it("reads a non-array under messages as a failed re-read, not as a transcript", async () => {
+    respondWith({ messages: { msg_open: OPEN } });
+    expect(await fetchChatTranscript("/agent/transcript", "chat_1")).toBeNull();
+  });
+
+  it("keeps only entries the merge can key on", async () => {
+    respondWith({ messages: [OPEN, null, "msg_open", { revision: 1 }, SETTLED] });
+    const fetched = await fetchChatTranscript<typeof OPEN>("/agent/transcript", "chat_1");
+    expect(fetched?.map((message) => message.id)).toEqual([OPEN.id, SETTLED.id]);
+  });
+
+  it("leaves the panel's transcript alone when the endpoint answers with a shape it cannot merge", async () => {
+    respondWith({ messages: { msg_open: OPEN } });
+    let rendered: (typeof OPEN)[] = [OPEN];
+
+    await pollSettledTranscript<typeof OPEN>({
+      fetchTranscript: () => fetchChatTranscript("/agent/transcript", "chat_1"),
+      apply: (merge) => void (rendered = merge(rendered)),
+      wait: async () => {},
+    });
+
+    expect(rendered).toEqual([OPEN]);
+  });
+});
+
 describe("an already-open panel when a turn is exhausted", () => {
   it("stops showing Working… without a reload or a reopen", async () => {
     // What the mounted panel holds when the stream closes: the card the model opened

apps/webapp/app/components/dashboard-agent/settled-transcript.ts

@@ -59,8 +59,15 @@ export async function fetchChatTranscript<T extends Identified>(
   try {
     const res = await fetch(`${actionPath}?chatId=${encodeURIComponent(chatId)}`);
     if (!res.ok) return null;
-    const data = (await res.json()) as { messages?: T[] };
-    return data.messages ?? null;
+    const data = (await res.json()) as { messages?: unknown };
+    if (!Array.isArray(data.messages)) return null;
+    // Anything else under `messages` is not a transcript; keep only what merging can key on.
+    return data.messages.filter(
+      (message): message is T =>
+        typeof message === "object" &&
+        message !== null &&
+        typeof (message as Identified).id === "string"
+    );
   } catch (error) {
     console.error("Dashboard agent: failed to re-read the settled transcript", error);
     return null;