fix(app): keep rewound history in its own chat

A restored fork snapshot belongs to the rewound agent. Give it an agent attachment scope so switching chats cannot send or consume that context elsewhere in the workspace.

packages/app/e2e/browser/assistant-fork-menu.spec.ts

@@ -1,5 +1,6 @@
 import {
   captureChatHistory,
+  expectRewoundHistoryIsPrivate,
   rewindForkPrompt,
   closeChatHistory,
   followChatHistorySource,
@@ -113,6 +114,7 @@ test.describe("Assistant fork menu", () => {
       await openChatHistory(page, "sent", [initialPrompt]);
       await closeChatHistory(page);
       await rewindForkPrompt(page);
+      await expectRewoundHistoryIsPrivate(page, session.agentId, forkId);
       await openChatHistory(page, "draft", [initialPrompt]);
       await closeChatHistory(page);
       await submitMessage(page, prompt);

packages/app/e2e/support/helpers/chat-history.ts

@@ -70,3 +70,13 @@ export async function rewindForkPrompt(page: Page) {
   await option.click();
   await expect(option).not.toBeVisible();
 }
+
+export async function expectRewoundHistoryIsPrivate(page: Page, sourceId: string, forkId: string) {
+  await page.getByTestId(`workspace-tab-agent_${sourceId}`).click();
+  const history = page
+    .getByTestId("composer-chat-history-attachment-pill")
+    .filter({ visible: true });
+  await expect(history).toHaveCount(0);
+  await page.getByTestId(`workspace-tab-agent_${forkId}`).click();
+  await expect(history).toBeVisible();
+}

packages/app/src/attachments/workspace-attachments-store.ts

@@ -178,6 +178,19 @@ export function useWorkspaceAttachmentScopeKey(input: WorkspaceAttachmentScope):
   }, [cwd, draftId, isDraftScope, serverId, workspaceId]);
 }
 
+export function useAgentAttachmentScopeKey(input: { serverId: string; agentId: string }): string {
+  const { serverId, agentId } = input;
+  return useMemo(
+    () =>
+      [
+        "agent-attachments",
+        `server=${encodeScopePart(serverId)}`,
+        `agent=${encodeScopePart(agentId)}`,
+      ].join(":"),
+    [serverId, agentId],
+  );
+}
+
 export function useDraftWorkspaceAttachmentScopeKey(draftId: string | null | undefined): string {
   const normalizedDraftId = useMemo(() => draftId?.trim() ?? "", [draftId]);
   return useMemo(

packages/app/src/panels/agent-panel.tsx

@@ -43,7 +43,10 @@ import { RewindComposerRestoreProvider } from "@/components/rewind/composer-rest
 import { useAgentDescriptor } from "@/agent-presentation";
 import { useToastHost, type ToastApi, type ToastState } from "@/components/toast-host";
 import type { WorkspaceComposerAttachment } from "@/attachments/types";
-import { useWorkspaceAttachmentScopeKey } from "@/attachments/workspace-attachments-store";
+import {
+  useWorkspaceAttachmentScopeKey,
+  useAgentAttachmentScopeKey,
+} from "@/attachments/workspace-attachments-store";
 import { COMPACT_CONTENT_WIDTH, useIsCompactFormFactor } from "@/constants/layout";
 import { isNative, isWeb } from "@/constants/platform";
 import { useAgentAttentionClear } from "@/hooks/use-agent-attention-clear";
@@ -1112,7 +1115,7 @@ const ChatAgentReadyContent = memo(function ChatAgentReadyContent({
   const parentAgentId = useParentAgentId(serverId, agentId);
   // With a composer the parent is a pill above it; without one, the box takes the composer's place.
   const parentPillAgentId = showsComposer ? parentAgentId : null;
-  const rewindAttachmentScopeKey = useWorkspaceAttachmentScopeKey({ serverId, workspaceId, cwd });
+  const rewindAttachmentScopeKey = useAgentAttachmentScopeKey({ serverId, agentId });
   const rawAgentInputDraft = useAgentInputDraft({
     draftKey: buildDraftStoreKey({
       serverId,
@@ -1543,9 +1546,10 @@ function ActiveAgentComposer({
     cwd,
     workspaceId,
   });
+  const agentAttachmentScopeKey = useAgentAttachmentScopeKey({ serverId, agentId });
   const attachmentScopeKeys = useMemo(
-    () => [workspaceAttachmentScopeKey],
-    [workspaceAttachmentScopeKey],
+    () => [workspaceAttachmentScopeKey, agentAttachmentScopeKey],
+    [workspaceAttachmentScopeKey, agentAttachmentScopeKey],
   );
   const handleOpenWorkspaceAttachment = useCallback(
     (attachment: WorkspaceComposerAttachment) => {