feat(chat): desktop prompt navigator rail (#2054)

* feat(chat): add desktop prompt navigator rail

Add a ChatGPT-style right-center prompt marker rail for web/desktop chat
with hover/keyboard preview panel, load-more for partial history (panel only),
Chat setting, and mod+alt+p shortcut. Disabled in VS Code across rail,
shortcut, settings, help, and search surfaces.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(ui): read promptNavigatorEnabled from getState in shortcut handler

Match the file convention used by other shortcut handlers so the toggle
does not rely on a hook-level selector closure.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

* fix(ui): drop use-no-memo and default prompt navigator off

Remove the project-unprecedented React Compiler opt-out, and ship the
prompt navigator as opt-in to match other recent chat UI toggles.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/stores/useUIStore.ts

@@ -612,6 +612,7 @@ interface UIStore {
   diffWrapLines: boolean;
   gitChangesViewMode: 'flat' | 'tree';
   isTimelineDialogOpen: boolean;
+  isPromptNavigatorPanelOpen: boolean;
   isImagePreviewOpen: boolean;
   nativeNotificationsEnabled: boolean;
   notificationMode: 'always' | 'hidden-only';
@@ -655,6 +656,7 @@ interface UIStore {
   userMessageRenderingMode: UserMessageRenderingMode;
   collapsibleUserMessages: boolean;
   stickyUserHeader: boolean;
+  promptNavigatorEnabled: boolean;
   expandedEditorToolbar: boolean;
   showSplitAssistantMessageActions: boolean;
   allowPromptingSubagentSessions: boolean;
@@ -780,6 +782,8 @@ interface UIStore {
   setGitChangesViewMode: (mode: 'flat' | 'tree') => void;
   setMultiRunLauncherOpen: (open: boolean) => void;
   setTimelineDialogOpen: (open: boolean) => void;
+  setPromptNavigatorPanelOpen: (open: boolean) => void;
+  togglePromptNavigatorPanel: () => void;
   setImagePreviewOpen: (open: boolean) => void;
   setNativeNotificationsEnabled: (value: boolean) => void;
   setNotificationMode: (mode: 'always' | 'hidden-only') => void;
@@ -810,6 +814,7 @@ interface UIStore {
   setUserMessageRenderingMode: (value: UserMessageRenderingMode) => void;
   setCollapsibleUserMessages: (value: boolean) => void;
   setStickyUserHeader: (value: boolean) => void;
+  setPromptNavigatorEnabled: (value: boolean) => void;
   setExpandedEditorToolbar: (value: boolean) => void;
   setShowSplitAssistantMessageActions: (value: boolean) => void;
   setAllowPromptingSubagentSessions: (value: boolean) => void;
@@ -918,6 +923,7 @@ export const useUIStore = create<UIStore>()(
         diffWrapLines: false,
         gitChangesViewMode: 'flat',
         isTimelineDialogOpen: false,
+        isPromptNavigatorPanelOpen: false,
         isImagePreviewOpen: false,
         nativeNotificationsEnabled: false,
         notificationMode: 'hidden-only',
@@ -958,6 +964,7 @@ export const useUIStore = create<UIStore>()(
         userMessageRenderingMode: 'markdown',
         collapsibleUserMessages: true,
         stickyUserHeader: false,
+        promptNavigatorEnabled: false,
         expandedEditorToolbar: false,
         showSplitAssistantMessageActions: false,
         allowPromptingSubagentSessions: false,
@@ -2037,6 +2044,14 @@ export const useUIStore = create<UIStore>()(
           set({ isTimelineDialogOpen: open });
         },
 
+        setPromptNavigatorPanelOpen: (open) => {
+          set({ isPromptNavigatorPanelOpen: open });
+        },
+
+        togglePromptNavigatorPanel: () => {
+          set((state) => ({ isPromptNavigatorPanelOpen: !state.isPromptNavigatorPanelOpen }));
+        },
+
         setImagePreviewOpen: (open) => {
           set({ isImagePreviewOpen: open });
         },
@@ -2119,6 +2134,9 @@ export const useUIStore = create<UIStore>()(
         setStickyUserHeader: (value) => {
           set({ stickyUserHeader: value });
         },
+        setPromptNavigatorEnabled: (value) => {
+          set({ promptNavigatorEnabled: value });
+        },
         setExpandedEditorToolbar: (value: boolean) => {
           set({ expandedEditorToolbar: value });
         },
@@ -2369,6 +2387,7 @@ export const useUIStore = create<UIStore>()(
           userMessageRenderingMode: state.userMessageRenderingMode,
           collapsibleUserMessages: state.collapsibleUserMessages,
           stickyUserHeader: state.stickyUserHeader,
+          promptNavigatorEnabled: state.promptNavigatorEnabled,
           expandedEditorToolbar: state.expandedEditorToolbar,
           showSplitAssistantMessageActions: state.showSplitAssistantMessageActions,
           allowPromptingSubagentSessions: state.allowPromptingSubagentSessions,