diff --git a/apps/web/src/components/ChatView.logic.test.ts b/apps/web/src/components/ChatView.logic.test.ts
index 330ab771c3f7..0ce4d137414e 100644
--- a/apps/web/src/components/ChatView.logic.test.ts
+++ b/apps/web/src/components/ChatView.logic.test.ts
@@ -1043,7 +1043,8 @@ describe("resolveThreadSwitchTimeline", () => {
 
   const held = { threadKey: "env-1:thread-a", entries: ["a1", "a2"] };
 
-  it("keeps the previous thread's entries while the next thread is loading", () => {
+  it("leaves an uncached destination empty while its history loads", () => {
+    rememberReadyThreadTimeline(held);
     expect(
       resolveThreadSwitchTimeline({
         loading: true,
@@ -1051,7 +1052,7 @@ describe("resolveThreadSwitchTimeline", () => {
         nextEntries: [],
         lastReady: held,
       }),
-    ).toEqual({ entries: ["a1", "a2"], displayThreadKey: "env-1:thread-a" });
+    ).toEqual({ entries: [], displayThreadKey: "env-1:thread-b" });
   });
 
   it("shows the new thread once its detail is ready", () => {
@@ -1089,18 +1090,6 @@ describe("resolveThreadSwitchTimeline", () => {
     });
   });
 
-  it("survives a ChatView remount by remembering the last ready timeline", () => {
-    rememberReadyThreadTimeline(held);
-    expect(peekHeldThreadTimeline<string[]>()).toEqual(held);
-    expect(
-      resolveThreadSwitchTimeline({
-        loading: true,
-        activeThreadKey: "env-1:thread-b",
-        nextEntries: [],
-      }),
-    ).toEqual({ entries: ["a1", "a2"], displayThreadKey: "env-1:thread-a" });
-  });
-
   it("paints a remembered destination instead of the last-viewed thread", () => {
     rememberReadyThreadTimeline(held);
     rememberReadyThreadTimeline({ threadKey: "env-1:thread-b", entries: ["b1", "b2"] });
diff --git a/apps/web/src/components/ChatView.logic.ts b/apps/web/src/components/ChatView.logic.ts
index 65807d965afe..7479a289d8ff 100644
--- a/apps/web/src/components/ChatView.logic.ts
+++ b/apps/web/src/components/ChatView.logic.ts
@@ -423,17 +423,6 @@ export function resolveThreadSwitchTimeline<T extends readonly unknown[]>(input:
     return { entries: rememberedForActive, displayThreadKey: input.activeThreadKey };
   }
 
-  const lastReady = input.lastReady ?? peekHeldThreadTimeline<T>();
-  if (
-    input.loading &&
-    lastReady !== null &&
-    lastReady.threadKey !== null &&
-    lastReady.threadKey !== input.activeThreadKey &&
-    lastReady.entries.length > 0 &&
-    threadKeysShareEnvironment(lastReady.threadKey, input.activeThreadKey)
-  ) {
-    return { entries: lastReady.entries, displayThreadKey: lastReady.threadKey };
-  }
   return { entries: input.nextEntries, displayThreadKey: input.activeThreadKey };
 }
 
diff --git a/apps/web/src/components/chat/WorkflowOpeningBlock.browser.test.tsx b/apps/web/src/components/chat/WorkflowOpeningBlock.browser.test.tsx
index e9ac0d4dca26..8f28e93b0081 100644
--- a/apps/web/src/components/chat/WorkflowOpeningBlock.browser.test.tsx
+++ b/apps/web/src/components/chat/WorkflowOpeningBlock.browser.test.tsx
@@ -5,6 +5,7 @@ import { createRoot, type Root } from "react-dom/client";
 import { afterEach, beforeEach, expect, it, vi } from "vite-plus/test";
 
 import "~/index.css";
+import { getSyntaxHighlighterPromise } from "../../lib/syntaxHighlighting";
 
 import { AppAtomRegistryProvider } from "../../rpc/atomRegistry";
 import { MarkdownFindContext } from "./markdownFindContext";
@@ -109,6 +110,9 @@ const foldToggle = () =>
 
 it("shows a short script as highlighted code with nothing to open", async () => {
   await render(SHORT_SCRIPT);
+  await act(async () => {
+    await getSyntaxHighlighterPromise("javascript");
+  });
   expect(host.querySelector('[data-language="javascript"]')?.textContent).toContain("SCRIPTONLY");
   await vi.waitFor(() => expect(host.querySelector(".chat-markdown-shiki")).not.toBeNull());
   expect(foldToggle()).toBeUndefined();
diff --git a/apps/web/src/components/files/AttachmentFilePreview.browser.test.tsx b/apps/web/src/components/files/AttachmentFilePreview.browser.test.tsx
index 1f3f1742ac2c..3ae2c3d998a8 100644
--- a/apps/web/src/components/files/AttachmentFilePreview.browser.test.tsx
+++ b/apps/web/src/components/files/AttachmentFilePreview.browser.test.tsx
@@ -69,6 +69,9 @@ describe("attachment HTML preview recovery", () => {
     expect(container.querySelector("iframe")?.getAttribute("src")).toBe(originalUrl);
     now = 61 * 60_000;
     await toggleMode("Show HTML source");
+    await act(async () => {
+      await import("./ReadOnlySourcePreview");
+    });
     expect(fetch).toHaveBeenCalledExactlyOnceWith(renewedUrl, expect.any(Object));
     await vi.waitFor(() =>
       expect(container.querySelector("pre")?.textContent).toBe("<p>Captured HTML</p>"),