fix(web-inspector): drop stale Try from here results

packages/web-inspector/src/__tests__/inspector-navigation.spec.ts

@@ -625,6 +625,67 @@ test("Try from here copies a stored thread into Playground without changing the
   }
 });
 
+test("Try from here discards a stale copy after leaving Threads", async () => {
+  const context = await setup({
+    agent: true,
+    agentIds: ["default"],
+    threads: [SAVED_THREAD],
+  });
+  try {
+    await context.open();
+    await context.selectLeaf("threads");
+    await selectSavedThread(context.inspector);
+
+    const pendingFetch = globalThis.fetch;
+    let releaseMessages!: () => void;
+    let messagesResolved = false;
+    const messagesGate = new Promise<void>((resolve) => {
+      releaseMessages = resolve;
+    });
+    vi.stubGlobal(
+      "fetch",
+      async (input: RequestInfo | URL, init?: RequestInit) => {
+        const url = input instanceof Request ? input.url : String(input);
+        const isMessages = url.endsWith("/threads/thread-1/messages");
+        if (isMessages) {
+          await messagesGate;
+        }
+        const response = await pendingFetch(input, init);
+        if (isMessages) {
+          messagesResolved = true;
+        }
+        return response;
+      },
+    );
+
+    const root = requireElement(
+      context.inspector.shadowRoot,
+      "Web Inspector shadow root was not rendered",
+    );
+    const button = requireElement(
+      tryFromHereButton(root),
+      "Try from here was not rendered",
+    );
+    button.click();
+    await context.selectLeaf("home");
+    expectCurrentNavigation(root, "home", "home");
+
+    releaseMessages();
+    await waitFor(() => messagesResolved, "stale Try from here load");
+    await context.inspector.updateComplete;
+
+    expectCurrentNavigation(root, "home", "home");
+    await context.selectLeaf("playground");
+    expect(root.textContent).not.toContain("Earlier answer");
+    expect(
+      root.querySelector<HTMLSelectElement>("#cpk-playground-thread-source")
+        ?.value ?? "",
+    ).not.toBe("thread-1");
+  } finally {
+    context.teardown();
+  }
+});
+
 test("Try from here stays on Threads when messages fail", async () => {
   const context = await setup({
     agent: true,

packages/web-inspector/src/index.ts

@@ -14779,19 +14779,28 @@ export class WebInspectorElement extends LitElement {
     this.tryFromHereError = null;
     this.requestUpdate();
 
+    const isCurrentTryFromHereRequest = (): boolean =>
+      this.selectedThreadId === threadId && this.selectedMenu === "threads";
+
     try {
       const snapshot = await this.loadThreadSnapshot(thread);
-      this.applyThreadSnapshotToPlayground(thread, snapshot);
+      // A later thread or pane change owns the UI. Keep the fetch outcome
+      // for telemetry, but do not replace Playground or leave Threads.
+      if (isCurrentTryFromHereRequest()) {
+        this.applyThreadSnapshotToPlayground(thread, snapshot);
+        this.handleMenuSelect("playground");
+      }
       if (!this.core?.telemetryDisabled) {
         trackThreadsTryFromHereClicked({
           ...this.getThreadsTelemetryProps(),
           outcome: "success",
         });
       }
-      this.handleMenuSelect("playground");
     } catch (error) {
-      this.tryFromHereError =
-        error instanceof Error ? error.message : "Failed to load thread.";
+      if (isCurrentTryFromHereRequest()) {
+        this.tryFromHereError =
+          error instanceof Error ? error.message : "Failed to load thread.";
+      }
       if (!this.core?.telemetryDisabled) {
         trackThreadsTryFromHereClicked({
           ...this.getThreadsTelemetryProps(),

prds/oss-873-try-from-here.md

@@ -82,7 +82,7 @@ The button is hidden on example tour threads and when thread inspect cannot load
   - Map stored thread messages onto Playground agent messages (user, assistant, tool), then `clone()` the source agent, assign a new Playground thread id, `setMessages`, `setState`.
 - Fetch the snapshot first. Replace the scratch session only after a successful messages load. This is the control flow from the grill (not a demo):
 
-```
+```text
 snapshot = loadThread(threadId)
 if snapshot.messagesFailed:
   showErrorOnThreads(error)