fix(settings): stabilize loading and reuse device-scoped snapshots

src/web-ui/src/app/scenes/settings/AGENTS.md

@@ -26,6 +26,14 @@ Follow `src/web-ui/AGENTS.md` and the settings control sizing rules in
   rename generated protocol IDs to match sidebar labels.
 - Moving a setting must preserve its execution host, remote capability gates,
   unsupported states, persistence keys, and draft registration.
+- Page preparation must retain the scene frame and use `SettingsPage` for its
+  fallback. First-load placeholders use `ConfigLoadingState` inside the content
+  frame; refreshes retain successful content. Seed editable forms only from a
+  complete `ConfigManager` snapshot, never from default values after a failed
+  read. Do not hydrate over edits or keep inactive page effects alive for caching.
+- Runtime snapshots and scroll positions belong to the current device activation.
+  Background responses must not repopulate a previous activation; section links
+  take precedence over restored scroll positions.
 
 ## Focused verification
 

src/web-ui/src/app/scenes/settings/SettingsNav.test.tsx

@@ -46,6 +46,7 @@ vi.mock('@/shared/utils/motionPreference', () => ({
 }));
 
 import SettingsNav from './SettingsNav';
+import { preloadSettingsPage } from './settingsRegistry';
 import { useSettingsStore } from './settingsStore';
 import {
   registerSettingsDraft,
@@ -58,6 +59,7 @@ describe('SettingsNav shared component composition', () => {
 
   beforeEach(() => {
     vi.useFakeTimers();
+    vi.mocked(preloadSettingsPage).mockReset().mockResolvedValue(undefined);
     resetSettingsDraftRegistryForTests();
     useSettingsStore.setState(useSettingsStore.getInitialState());
     container = document.createElement('div');
@@ -183,4 +185,35 @@ describe('SettingsNav shared component composition', () => {
     expect(useSettingsStore.getState().activePageId).toBe('application.pet');
     expect(useSettingsStore.getState().activeSectionId).toBeNull();
   });
+  it('marks a slow destination pending before showing its loading page', async () => {
+    vi.mocked(preloadSettingsPage).mockReturnValue(new Promise(() => {}));
+    const item = container.querySelector('[data-settings-page="application.appearance"]') as HTMLButtonElement;
+    await act(async () => item.click());
+    expect(item.getAttribute('aria-busy')).toBe('true');
+    expect(useSettingsStore.getState().activePageId).toBe('application.general');
+    await act(async () => vi.advanceTimersByTimeAsync(180));
+    expect(useSettingsStore.getState().activePageId).toBe('application.appearance');
+    expect(item.hasAttribute('aria-busy')).toBe(false);
+  });
+
+  it('ignores an earlier click when its preload completes after the latest selection', async () => {
+    let finishOld!: () => void;
+    vi.mocked(preloadSettingsPage).mockImplementation(pageId => pageId === 'application.appearance'
+      ? new Promise<void>(resolve => { finishOld = resolve; }) : Promise.resolve());
+    await act(async () => (container.querySelector('[data-settings-page="application.appearance"]') as HTMLButtonElement).click());
+    await act(async () => (container.querySelector('[data-settings-page="application.pet"]') as HTMLButtonElement).click());
+    await act(async () => finishOld());
+    await act(async () => vi.advanceTimersByTimeAsync(180));
+    expect(useSettingsStore.getState().activePageId).toBe('application.pet');
+  });
+
+  it('does not override a newer programmatic destination with a pending click', async () => {
+    let finish!: () => void;
+    vi.mocked(preloadSettingsPage).mockReturnValue(new Promise<void>(resolve => { finish = resolve; }));
+    await act(async () => (container.querySelector('[data-settings-page="application.appearance"]') as HTMLButtonElement).click());
+    await act(async () => useSettingsStore.getState().openPage('application.pet'));
+    await act(async () => finish());
+    expect(useSettingsStore.getState().activePageId).toBe('application.pet');
+  });
+
 });

src/web-ui/src/app/scenes/settings/SettingsNav.tsx

@@ -1,4 +1,5 @@
 import { useSettingsDraftSnapshot } from '@/infrastructure/config/settingsDraftRegistry';
+import { getActiveSurfaceScope } from '@/infrastructure/peer-device/deviceSurface';
 import { useI18n } from '@/infrastructure/i18n/hooks/useI18n';
 import { getInteractionMotion } from '@/shared/utils/motionPreference';
 import {
@@ -11,10 +12,10 @@ import {
   NavigationPanelSection,
   OverflowText,
   SearchField,
+  Spinner,
 } from '@openbitfun/ui';
 import type { i18n as I18nApi } from 'i18next';
 import React, {
-  startTransition,
   useCallback,
   useEffect,
   useMemo,
@@ -138,6 +139,13 @@ const SettingsNav: React.FC = () => {
   const searchInputRef = useRef<HTMLInputElement>(null);
   const resultsRef = useRef<HTMLDivElement>(null);
   const activationRequestRef = useRef(0);
+  const [pendingPageId, setPendingPageId] = useState<SettingsPageId | null>(null);
+  const activationTimerRef = useRef<number | undefined>();
+
+  useEffect(() => () => {
+    activationRequestRef.current += 1;
+    window.clearTimeout(activationTimerRef.current);
+  }, []);
 
   useEffect(() => {
     const timer = window.setTimeout(() => setSearchQuery(draftQuery), SEARCH_DEBOUNCE_MS);
@@ -186,14 +194,27 @@ const SettingsNav: React.FC = () => {
 
   const activate = useCallback((destination: SettingsDestination, clear = false) => {
     const requestId = ++activationRequestRef.current;
+    const scope = getActiveSurfaceScope();
+    const navigationRequestId = useSettingsStore.getState().navigationRequestId;
     const motion = getInteractionMotion();
+    window.clearTimeout(activationTimerRef.current);
+    setPendingPageId(destination.pageId);
+    let committed = false;
     const commit = () => {
-      if (requestId !== activationRequestRef.current) return;
-      startTransition(() => {
-        openDestination(destination, motion);
-        if (clear) clearSearch();
-      });
+      if (committed || requestId !== activationRequestRef.current) return;
+      if (!scope.isCurrent() || useSettingsStore.getState().navigationRequestId !== navigationRequestId) {
+        window.clearTimeout(activationTimerRef.current);
+        setPendingPageId(null);
+        return;
+      }
+      committed = true;
+      window.clearTimeout(activationTimerRef.current);
+      setPendingPageId(null);
+      openDestination(destination, motion);
+      if (clear) clearSearch();
     };
+    // Keep the current page during fast preparation; slow loads get a titled skeleton.
+    activationTimerRef.current = window.setTimeout(commit, 180);
     void preloadSettingsPage(destination.pageId).then(commit, commit);
   }, [clearSearch, openDestination]);
 
@@ -301,6 +322,7 @@ const SettingsNav: React.FC = () => {
                       id={`settings-nav-result-${index}`}
                       role="option"
                       aria-selected={active}
+                      aria-busy={pendingPageId === row.destination.pageId || undefined}
                       selected={active}
                       data-openbitfun-component="settings-nav"
                       data-openbitfun-part="searchResult"
@@ -325,7 +347,7 @@ const SettingsNav: React.FC = () => {
                           {highlightFirstMatch(row.description, searchQuery)}
                         </OverflowText>
                       </span>
-                      {dirtyMarker(row.destination.pageId)}
+                      {pendingPageId === row.destination.pageId ? <Spinner size="sm" /> : dirtyMarker(row.destination.pageId)}
                     </NavigationPanelItem>
                   );
                 })}
@@ -362,12 +384,13 @@ const SettingsNav: React.FC = () => {
                     data-openbitfun-state={activePageId === page.id ? 'active' : undefined}
                     className="openbitfun-settings-nav__item"
                     selected={activePageId === page.id}
+                    aria-busy={pendingPageId === page.id || undefined}
                     onClick={() => activate({ pageId: page.id })}
                     onPointerEnter={() => preload(page.id)}
                     onFocus={() => preload(page.id)}
                   >
                     <OverflowText className="openbitfun-settings-nav__item-label">{t(page.labelKey)}</OverflowText>
-                    {dirtyMarker(page.id)}
+                    {pendingPageId === page.id ? <Spinner size="sm" /> : dirtyMarker(page.id)}
                   </NavigationPanelItem>
                 ))}
               </div>

src/web-ui/src/app/scenes/settings/SettingsScene.scss

@@ -9,57 +9,6 @@
   height: 100%;
   overflow: hidden;
 
-  &__loading {
-    flex: 1;
-    padding: var(--openbitfun-space-6);
-  }
-
-  &__loading-line,
-  &__loading-block {
-    border-radius: var(--openbitfun-radius-md);
-    background: var(--openbitfun-color-action-quiet-hover);
-    opacity: 0.65;
-  }
-
-  &__loading-line {
-    height: 14px;
-    max-width: 360px;
-    margin-bottom: var(--openbitfun-space-3);
-
-    &--title {
-      height: 20px;
-      max-width: 220px;
-      margin-bottom: var(--openbitfun-space-5);
-    }
-  }
-
-  &__loading-block {
-    height: 160px;
-    max-width: 720px;
-    margin-top: var(--openbitfun-space-6);
-  }
-
-  &__content-stack {
-    flex: 1;
-    min-width: 0;
-    min-height: 0;
-    overflow: hidden;
-  }
-
-  &__content-transition {
-    flex: 1 1 auto;
-    width: 100%;
-    height: 100%;
-    min-width: 0;
-    min-height: 0;
-    overflow: hidden;
-
-    > .openbitfun-view-transition-boundary__view {
-      width: 100%;
-      height: 100%;
-    }
-  }
-
   &__content-wrapper {
     display: flex;
     flex-direction: column;

src/web-ui/src/app/scenes/settings/SettingsScene.test.tsx

@@ -4,6 +4,19 @@ import React, { act } from 'react';
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { createRoot, type Root } from 'react-dom/client';
 
+const preparation = vi.hoisted(() => ({
+  ready: vi.fn(() => true),
+  preload: vi.fn(async (_pageId: string) => undefined),
+  loading: vi.fn(),
+}));
+vi.mock('./pages/shared/SettingsPage', () => ({
+  SettingsPage: ({ pageId, children }: { pageId: string; children: React.ReactNode }) => <section><h2>{pageId}</h2>{children}</section>,
+}));
+vi.mock('@/infrastructure/config/components/common', () => ({
+  ConfigLoadingState: () => { preparation.loading(); return <div data-testid="pending-page" />; },
+  ConfigRetryState: ({ onRetry }: { onRetry: () => void }) => <button data-testid="retry-page" onClick={onRetry}>Retry</button>,
+}));
+
 vi.mock('./settingsRegistry', () => {
   const pages = {
     'application.general': {
@@ -33,12 +46,13 @@ vi.mock('./settingsRegistry', () => {
     DEFAULT_SETTINGS_PAGE_ID: 'application.general',
     getSettingsPageManifest: (pageId: keyof typeof pages) => pages[pageId] ?? pages['application.general'],
     isSettingsPageId: (value: string) => value in pages,
-    isSettingsPageReady: () => true,
-    preloadSettingsPage: vi.fn(async () => undefined),
+    isSettingsPageReady: preparation.ready,
+    preloadSettingsPage: preparation.preload,
   };
 });
 
 import SettingsScene from './SettingsScene';
+import { activateSurface } from '@/infrastructure/peer-device/deviceSurface';
 import { useSettingsStore } from './settingsStore';
 import {
   registerSettingsDraft,
@@ -50,6 +64,9 @@ describe('SettingsScene canonical page routing', () => {
   let root: Root;
 
   beforeEach(() => {
+    preparation.ready.mockReset().mockReturnValue(true);
+    preparation.preload.mockReset().mockResolvedValue(undefined);
+    preparation.loading.mockClear();
     resetSettingsDraftRegistryForTests();
     container = document.createElement('div');
     document.body.appendChild(container);
@@ -135,4 +152,49 @@ describe('SettingsScene canonical page routing', () => {
     expect(save).toHaveBeenCalledOnce();
     expect(useSettingsStore.getState().activePageId).toBe('application.appearance');
   });
+  it('never mounts loading UI while switching between prepared pages', async () => {
+    await act(async () => root.render(<SettingsScene />));
+    const frame = container.querySelector('.openbitfun-settings-scene__content-wrapper');
+    await act(async () => useSettingsStore.getState().openPage('application.appearance', 'pointer'));
+    await act(async () => useSettingsStore.getState().openPage('application.general', 'pointer'));
+    expect(preparation.loading).not.toHaveBeenCalled();
+    expect(container.querySelector('.openbitfun-settings-scene__content-wrapper')).toBe(frame);
+    expect(container.querySelectorAll('[data-testid="settings-scene-content"]')).toHaveLength(1);
+  });
+
+  it('keeps the latest destination when cold imports complete out of order', async () => {
+    let finishAppearance!: () => void;
+    let finishAutomation!: () => void;
+    preparation.ready.mockReturnValue(false);
+    preparation.preload.mockImplementation(pageId => new Promise<void>(resolve => {
+      if (pageId === 'application.appearance') finishAppearance = resolve;
+      else finishAutomation = resolve;
+    }));
+    useSettingsStore.getState().openPage('application.appearance');
+    await act(async () => root.render(<SettingsScene />));
+    await act(async () => useSettingsStore.getState().openPage('tools.automation'));
+    await act(async () => finishAppearance());
+    expect(container.querySelector('h2')?.textContent).toBe('tools.automation');
+    expect(container.querySelector('[data-testid="appearance-page"]')).toBeNull();
+    await act(async () => finishAutomation());
+    expect(container.querySelector('[data-testid="automation-page"]')).not.toBeNull();
+  });
+
+  it('shows an in-place retry when preparation fails and recovers without leaving settings', async () => {
+    preparation.ready.mockReturnValue(false);
+    preparation.preload.mockRejectedValueOnce(new Error('offline'));
+    await act(async () => root.render(<SettingsScene />));
+    expect(container.querySelector('[data-testid="retry-page"]')).not.toBeNull();
+    expect(container.querySelector('[data-testid="general-page"]')).toBeNull();
+    await act(async () => (container.querySelector('[data-testid="retry-page"]') as HTMLButtonElement).click());
+    expect(container.querySelector('[data-testid="general-page"]')).not.toBeNull();
+  });
+
+  it('replaces page-local state synchronously on device activation', async () => {
+    await act(async () => root.render(<SettingsScene />));
+    const oldPage = container.querySelector('[data-testid="general-page"]');
+    await act(async () => activateSurface('peer-settings-test'));
+    expect(container.querySelector('[data-testid="general-page"]')).not.toBe(oldPage);
+  });
+
 });