diff --git a/apps/web/src/components/DesignFilesPanel.tsx b/apps/web/src/components/DesignFilesPanel.tsx
index b719f9b6fb..914a075c22 100644
--- a/apps/web/src/components/DesignFilesPanel.tsx
+++ b/apps/web/src/components/DesignFilesPanel.tsx
@@ -39,6 +39,70 @@ type DesignFilesGroupMode = 'kind' | 'modified';
 type ModifiedSection = 'today' | 'yesterday' | 'previous7Days' | 'previous30Days' | 'older';
 type SortKey = 'name' | 'kind' | 'mtime';
 type SortDir = 'asc' | 'desc';
+
+// Storage key for per-project view state. Bump the version suffix (v1 → v2) when
+// removing or renaming a persisted field — just adding an optional field is safe
+// without a version bump. No cleanup of old keys on project deletion; the keys
+// are small preference blobs and orphan gracefully.
+const VIEW_STATE_KEY_PREFIX = 'od:design-files:view-state:v1:';
+
+const DEFAULT_SORT_KEY: SortKey = 'mtime';
+const DEFAULT_SORT_DIR: SortDir = 'desc';
+const DEFAULT_PAGE_SIZE: number | 'all' = 30;
+const PAGE_SIZE_OPTIONS = [15, 30, 45, 60, 'all'] as const;
+
+interface PersistedViewState {
+  sortKey?: SortKey;
+  sortDir?: SortDir;
+  pageSize?: number | 'all';
+  kindFilter?: string[];
+}
+
+function readViewState(projectId: string): PersistedViewState {
+  try {
+    if (typeof window === 'undefined') return {};
+    const raw = localStorage.getItem(VIEW_STATE_KEY_PREFIX + projectId);
+    if (!raw) return {};
+    const parsed = JSON.parse(raw) as unknown;
+    if (!parsed || typeof parsed !== 'object' || Array.isArray(parsed)) return {};
+    return parsed as PersistedViewState;
+  } catch {
+    return {};
+  }
+}
+
+function writeViewState(projectId: string, state: PersistedViewState): void {
+  try {
+    localStorage.setItem(VIEW_STATE_KEY_PREFIX + projectId, JSON.stringify(state));
+  } catch {
+    // localStorage unavailable (private mode, quota exceeded) — silently skip
+  }
+}
+
+function isSortKey(v: unknown): v is SortKey {
+  return v === 'name' || v === 'kind' || v === 'mtime';
+}
+
+function isSortDir(v: unknown): v is SortDir {
+  return v === 'asc' || v === 'desc';
+}
+
+function isPageSize(v: unknown): v is number | 'all' {
+  return (PAGE_SIZE_OPTIONS as ReadonlyArray<unknown>).includes(v);
+}
+
+// Validate that a value is one of the known ProjectFileKind literals. This
+// guards against stored values that were valid under a previous schema but
+// are no longer part of the union — they are silently dropped rather than
+// poisoning the kindFilter state.
+const VALID_KIND_SET: ReadonlySet<string> = new Set<ProjectFileKind>([
+  'html', 'image', 'video', 'audio', 'sketch', 'text',
+  'code', 'pdf', 'document', 'presentation', 'spreadsheet', 'binary',
+]);
+
+function isProjectFileKind(v: unknown): v is ProjectFileKind {
+  return typeof v === 'string' && VALID_KIND_SET.has(v);
+}
 type FileSystemEntryWithReader = FileSystemEntry & {
   createReader?: () => FileSystemDirectoryReader;
 };
@@ -102,8 +166,27 @@ export function DesignFilesPanel({
   const MENU_SAFE_PADDING = 8;
   const [preview, setPreview] = useState<string | null>(null);
   const [selected, setSelected] = useState<Set<string>>(new Set());
-  const [sortKey, setSortKey] = useState<SortKey>('mtime');
-  const [sortDir, setSortDir] = useState<SortDir>('desc');
+  // Read once at mount; projectId is stable for this component instance
+  // (parent uses key={projectId} to remount on project switch).
+  const savedViewState = useRef(readViewState(projectId));
+  // Guard for the persist useEffect: skip the initial write so we only
+  // flush to localStorage when the user actually changes a preference.
+  // Without this, every project the user opens gets a default-value entry
+  // written on first render, making stale-key garbage grow unbounded.
+  // Note: React 18 StrictMode (active in next dev) fires effects twice,
+  // keeping refs intact across the simulated remount. This means the guard
+  // fires on the first effect run, sets the ref true, and the second run
+  // then writes the defaults. The result is a harmless default-value entry
+  // for the project; subsequent user changes overwrite it correctly. The
+  // invariant ("no write without a user action") only holds in production
+  // builds where StrictMode is not active.
+  const viewStateHasMounted = useRef(false);
+  const [sortKey, setSortKey] = useState<SortKey>(
+    () => isSortKey(savedViewState.current.sortKey) ? savedViewState.current.sortKey : DEFAULT_SORT_KEY,
+  );
+  const [sortDir, setSortDir] = useState<SortDir>(
+    () => isSortDir(savedViewState.current.sortDir) ? savedViewState.current.sortDir : DEFAULT_SORT_DIR,
+  );
   const lastKeyPress = useRef<Map<string, number>>(new Map());
   const [deleting, setDeleting] = useState(false);
   const [installingFolder, setInstallingFolder] = useState<string | null>(null);
@@ -115,7 +198,13 @@ export function DesignFilesPanel({
   >(new Set());
   const [renaming, setRenaming] = useState<{ name: string; draft: string; saving: boolean } | null>(null);
   const [dayBoundary, setDayBoundary] = useState(() => Date.now());
-  const [kindFilter, setKindFilter] = useState<Set<ProjectFileKind>>(() => new Set());
+  const [kindFilter, setKindFilter] = useState<Set<ProjectFileKind>>(() => {
+    const { kindFilter: kf } = savedViewState.current;
+    if (!Array.isArray(kf) || kf.length === 0) return new Set();
+    // Validate each stored value against the current ProjectFileKind union so
+    // stale values from a prior schema (e.g. a renamed kind) are dropped silently.
+    return new Set(kf.filter(isProjectFileKind));
+  });
   const [filterMenuOpen, setFilterMenuOpen] = useState(false);
   const filterMenuRef = useRef<HTMLDivElement | null>(null);
 
@@ -136,7 +225,12 @@ export function DesignFilesPanel({
   // Drop any selected-filter kinds that no longer appear in the file list
   // (e.g. after a delete leaves the kind empty). Keeps the filter UI honest
   // and prevents a stale filter from silently hiding everything.
+  // Guard: skip when no kinds are available yet — availableKinds is empty only
+  // when files haven't loaded. Running cleanup against an empty set would
+  // clear a kindFilter that was correctly restored from localStorage before
+  // the async file list arrived.
   useEffect(() => {
+    if (availableKinds.length === 0) return;
     setKindFilter((prev) => {
       if (prev.size === 0) return prev;
       const present = new Set(availableKinds);
@@ -166,7 +260,9 @@ export function DesignFilesPanel({
   }, [filteredFiles, sortKey, sortDir]);
 
   const [page, setPage] = useState(0);
-  const [pageSize, setPageSize] = useState<number | 'all'>(30);
+  const [pageSize, setPageSize] = useState<number | 'all'>(
+    () => isPageSize(savedViewState.current.pageSize) ? savedViewState.current.pageSize : DEFAULT_PAGE_SIZE,
+  );
 
   const effectivePageSize = pageSize === 'all' ? Math.max(1, sortedFiles.length) : pageSize;
   const totalPages = Math.max(1, Math.ceil(sortedFiles.length / effectivePageSize));
@@ -207,6 +303,23 @@ export function DesignFilesPanel({
     setPage(0);
   }, [pageSize]);
 
+  // Persist view state so it survives navigation (the panel remounts via
+  // key={projectId} when the user tabs away and back).
+  // Skip the initial render: we only want to write when the user actually
+  // changes a preference, not on every project the user visits.
+  useEffect(() => {
+    if (!viewStateHasMounted.current) {
+      viewStateHasMounted.current = true;
+      return;
+    }
+    writeViewState(projectId, {
+      sortKey,
+      sortDir,
+      pageSize,
+      kindFilter: Array.from(kindFilter),
+    });
+  }, [projectId, sortKey, sortDir, pageSize, kindFilter]);
+
   // Reset to the first page when the filter changes — the previous page
   // index may no longer exist (or may now sit past the new totalPages).
   useEffect(() => {
@@ -1040,6 +1153,7 @@ export function DesignFilesPanel({
                       <label>
                         {t('designFiles.perPage')}:
                         <select
+                          data-testid="df-page-size-select"
                           value={pageSize === 'all' ? 'all' : pageSize}
                           onChange={(e) => {
                             const val = e.target.value;
diff --git a/apps/web/tests/components/DesignFilesPanel.test.tsx b/apps/web/tests/components/DesignFilesPanel.test.tsx
index ea92332907..a785d2d34c 100644
--- a/apps/web/tests/components/DesignFilesPanel.test.tsx
+++ b/apps/web/tests/components/DesignFilesPanel.test.tsx
@@ -1,11 +1,21 @@
 // @vitest-environment jsdom
 
 import { act, cleanup, fireEvent, render, screen, waitFor, within } from '@testing-library/react';
-import { afterEach, describe, expect, it, vi } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 
 import { DesignFilesPanel } from '../../src/components/DesignFilesPanel';
 import type { ProjectFile, ProjectFileKind } from '../../src/types';
 
+// Stub localStorage so the component's view-state persistence writes to an
+// in-memory store. Cleared in beforeEach so no test bleeds state into the next.
+const lsStore = new Map<string, string>();
+vi.stubGlobal('localStorage', {
+  getItem: (key: string) => lsStore.get(key) ?? null,
+  setItem: (key: string, value: string) => { lsStore.set(key, value); },
+  removeItem: (key: string) => { lsStore.delete(key); },
+  clear: () => { lsStore.clear(); },
+});
+
 function extForKind(kind: ProjectFileKind): string {
   if (kind === 'html') return 'html';
   if (kind === 'image') return 'png';
@@ -80,6 +90,10 @@ function getSelects(container: HTMLElement) {
 }
 
 describe('DesignFilesPanel grouping', () => {
+  beforeEach(() => {
+    lsStore.clear();
+  });
+
   afterEach(() => {
     cleanup();
     vi.useRealTimers();
@@ -297,6 +311,14 @@ describe('DesignFilesPanel grouping', () => {
 });
 
 describe('DesignFilesPanel large-list regression', () => {
+  beforeEach(() => {
+    lsStore.clear();
+  });
+
+  afterEach(() => {
+    cleanup();
+  });
+
   it('renders only the default page size (30) rows with 500 files', () => {
     const files = generateFiles(500);
     const { container } = renderPanel(files);
diff --git a/apps/web/tests/components/DesignFilesPanel.view-state-persist.test.tsx b/apps/web/tests/components/DesignFilesPanel.view-state-persist.test.tsx
new file mode 100644
index 0000000000..cab38c3904
--- /dev/null
+++ b/apps/web/tests/components/DesignFilesPanel.view-state-persist.test.tsx
@@ -0,0 +1,191 @@
+// @vitest-environment jsdom
+//
+// Red spec for bug #3a: view state (pageSize, sortKey, sortDir, kindFilter)
+// resets on navigation because the component remounts via key={projectId}.
+// These tests must go RED on origin/main and GREEN after the fix.
+
+import { cleanup, fireEvent, render } from '@testing-library/react';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { DesignFilesPanel } from '../../src/components/DesignFilesPanel';
+import type { ProjectFile, ProjectFileKind } from '../../src/types';
+
+// Minimal localStorage stub mirroring the pattern in state/config.test.ts
+const store = new Map<string, string>();
+vi.stubGlobal('localStorage', {
+  getItem: vi.fn((key: string) => store.get(key) ?? null),
+  setItem: vi.fn((key: string, value: string) => {
+    store.set(key, value);
+  }),
+  removeItem: vi.fn((key: string) => {
+    store.delete(key);
+  }),
+  clear: vi.fn(() => {
+    store.clear();
+  }),
+});
+
+function file(name: string, kind: ProjectFileKind = 'html', mtime = Date.now()): ProjectFile {
+  return { path: name, name, type: 'file', size: 1024, mtime, kind, mime: 'text/html' };
+}
+
+function generateFiles(count: number): ProjectFile[] {
+  const kinds: ProjectFileKind[] = ['html', 'image', 'sketch', 'text', 'code', 'pdf'];
+  return Array.from({ length: count }, (_, i) => {
+    const kind = kinds[i % kinds.length]!;
+    return file(`file-${i + 1}.html`, kind, Date.now() - i * 60_000);
+  });
+}
+
+function renderPanel(
+  files: ProjectFile[],
+  projectId = 'proj-a',
+) {
+  return render(
+    <DesignFilesPanel
+      projectId={projectId}
+      files={files}
+      liveArtifacts={[]}
+      onRefreshFiles={vi.fn()}
+      onOpenFile={vi.fn()}
+      onOpenLiveArtifact={vi.fn()}
+      onRenameFile={vi.fn()}
+      onDeleteFile={vi.fn()}
+      onDeleteFiles={vi.fn()}
+      onUpload={vi.fn()}
+      onUploadFiles={vi.fn()}
+      onPaste={vi.fn()}
+      onNewSketch={vi.fn()}
+    />,
+  );
+}
+
+function getPerPageSelect(container: HTMLElement): HTMLSelectElement {
+  // The per-page select is the first select in the panel
+  return container.querySelector<HTMLSelectElement>('.df-pagination-start select')!;
+}
+
+function getSortBtn(container: HTMLElement, label: string): HTMLElement {
+  return Array.from(container.querySelectorAll<HTMLElement>('.df-th-btn')).find(
+    (el) => el.textContent?.trim().startsWith(label),
+  )!;
+}
+
+describe('DesignFilesPanel view-state persistence', () => {
+  beforeEach(() => {
+    store.clear();
+    vi.mocked(localStorage.getItem).mockClear();
+    vi.mocked(localStorage.setItem).mockClear();
+  });
+
+  afterEach(() => {
+    cleanup();
+  });
+
+  it('restores pageSize from localStorage after remount', () => {
+    const files = generateFiles(500);
+
+    // First mount: change page size to 60
+    const first = renderPanel(files);
+    const sel = getPerPageSelect(first.container);
+    fireEvent.change(sel, { target: { value: '60' } });
+    first.unmount();
+
+    // Second mount simulates navigation away and back (key={projectId} causes remount)
+    const second = renderPanel(files);
+    const restoredSel = getPerPageSelect(second.container);
+    expect(restoredSel.value).toBe('60');
+  });
+
+  it('restores sort key from localStorage after remount', () => {
+    const files = generateFiles(50);
+
+    // First mount: click "Name" header to sort by name
+    const first = renderPanel(files);
+    fireEvent.click(getSortBtn(first.container, 'Name'));
+    first.unmount();
+
+    // Second mount: "Name" column should show the sort arrow
+    const second = renderPanel(files);
+    const nameBtn = getSortBtn(second.container, 'Name');
+    expect(nameBtn.textContent).toContain('↑');
+  });
+
+  it('restores sort direction from localStorage after remount', () => {
+    const files = generateFiles(50);
+
+    // First mount: click "Name" twice to get desc
+    const first = renderPanel(files);
+    fireEvent.click(getSortBtn(first.container, 'Name'));
+    fireEvent.click(getSortBtn(first.container, 'Name'));
+    first.unmount();
+
+    // Second mount: Name column should show desc arrow
+    const second = renderPanel(files);
+    const nameBtn = getSortBtn(second.container, 'Name');
+    expect(nameBtn.textContent).toContain('↓');
+  });
+
+  it('restores kindFilter from localStorage after remount', () => {
+    // Files with mixed kinds so the filter button appears
+    const files = [
+      file('a.html', 'html'),
+      file('b.png', 'image'),
+      file('c.txt', 'text'),
+    ];
+
+    // First mount: open the filter popover and check 'HTML page'
+    const first = renderPanel(files);
+    const filterTrigger = first.container.querySelector<HTMLElement>('.df-kind-filter-trigger');
+    expect(filterTrigger).not.toBeNull();
+    fireEvent.click(filterTrigger!);
+    const checkboxes = first.container.querySelectorAll<HTMLInputElement>(
+      '.df-kind-filter-list input[type="checkbox"]',
+    );
+    // Check the first checkbox (HTML)
+    if (checkboxes[0]) fireEvent.click(checkboxes[0]);
+    first.unmount();
+
+    // Second mount: filter button should show active state (a kind is selected)
+    const second = renderPanel(files);
+    const trigger = second.container.querySelector('.df-kind-filter-trigger');
+    expect(trigger?.classList.contains('active')).toBe(true);
+  });
+
+  it('does not bleed pageSize from one project into another', () => {
+    const files = generateFiles(500);
+
+    // Project A: set page size 60
+    const first = renderPanel(files, 'proj-a');
+    fireEvent.change(getPerPageSelect(first.container), { target: { value: '60' } });
+    first.unmount();
+
+    // Project B: should still have the default (30), not project A's setting
+    const second = renderPanel(files, 'proj-b');
+    expect(getPerPageSelect(second.container).value).toBe('30');
+  });
+
+  it('writes view state to localStorage on pageSize change', () => {
+    const files = generateFiles(500);
+    const { container } = renderPanel(files);
+
+    fireEvent.change(getPerPageSelect(container), { target: { value: '45' } });
+
+    expect(vi.mocked(localStorage.setItem)).toHaveBeenCalledWith(
+      expect.stringMatching(/od:design-files:view-state/),
+      expect.any(String),
+    );
+  });
+
+  it('falls back to default pageSize when stored value is not a supported option', () => {
+    const files = generateFiles(500);
+
+    // Seed localStorage with an unsupported value (fractional, out-of-set integer)
+    for (const bad of [0.5, 17, 999, -1, 0]) {
+      vi.mocked(localStorage.getItem).mockReturnValueOnce(JSON.stringify({ pageSize: bad }));
+      const { container } = renderPanel(files);
+      expect(getPerPageSelect(container).value).toBe('30');
+      cleanup();
+    }
+  });
+});
diff --git a/e2e/ui/design-files-view-state-persist.test.ts b/e2e/ui/design-files-view-state-persist.test.ts
new file mode 100644
index 0000000000..16f6692c06
--- /dev/null
+++ b/e2e/ui/design-files-view-state-persist.test.ts
@@ -0,0 +1,361 @@
+/**
+ * Verifies that the DesignFilesPanel view state (sortKey, sortDir, pageSize,
+ * kindFilter) is written to localStorage under the per-project key
+ * 'od:design-files:view-state:v1:<projectId>' and is restored correctly
+ * across three scenarios:
+ *
+ *   (a) Tab-away / tab-back: navigating to a file tab and returning remounts
+ *       the panel; prefs must survive.
+ *   (b) Hard reload: localStorage persists across page.reload(); prefs must
+ *       survive.
+ *   (c) Project isolation: opening a second project starts with defaults, NOT
+ *       the first project's persisted state.
+ *
+ * Each test must PASS on fix/web-design-files-persist-view and FAIL on
+ * origin/main (where no persistence is implemented).
+ */
+
+import { expect, test } from '@playwright/test';
+import type { Page } from '@playwright/test';
+
+// Matches the constant in DesignFilesPanel.tsx
+const VIEW_STATE_KEY_PREFIX = 'od:design-files:view-state:v1:';
+
+// Config key expected by the web app to skip onboarding
+const CONFIG_STORAGE_KEY = 'open-design:config';
+
+// Minimal 1x1 PNG, base64-encoded
+const TINY_PNG_B64 =
+  'iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mP8/x8AAwMCAO5W6McAAAAASUVORK5CYII=';
+
+// 90 s: each test seeds ~18 files via sequential POST requests; on a cold CI
+// runner this alone takes 40-50 s before any assertion.
+test.describe.configure({ timeout: 90_000 });
+
+// Inject onboarding bypass and mock app-config before each test so the web app
+// boots straight into the workspace without prompts.
+test.beforeEach(async ({ page }) => {
+  await page.addInitScript((key) => {
+    window.localStorage.setItem(
+      key,
+      JSON.stringify({
+        mode: 'daemon',
+        apiKey: '',
+        baseUrl: 'https://api.anthropic.com',
+        model: 'claude-sonnet-4-5',
+        agentId: 'mock',
+        skillId: null,
+        designSystemId: null,
+        onboardingCompleted: true,
+        agentModels: {},
+        privacyDecisionAt: 1,
+        telemetry: { metrics: false, content: false, artifactManifest: false },
+      }),
+    );
+  }, CONFIG_STORAGE_KEY);
+
+  await page.route('**/api/app-config', async (route) => {
+    if (route.request().method() !== 'GET') {
+      await route.continue();
+      return;
+    }
+    await route.fulfill({
+      json: {
+        config: {
+          onboardingCompleted: true,
+          agentId: 'mock',
+          skillId: null,
+          designSystemId: null,
+          agentModels: {},
+          privacyDecisionAt: 1,
+          telemetry: { metrics: false, content: false, artifactManifest: false },
+        },
+      },
+    });
+  });
+
+  await page.route('**/api/agents', async (route) => {
+    await route.fulfill({
+      json: {
+        agents: [
+          {
+            id: 'mock',
+            name: 'Mock Agent',
+            bin: 'mock-agent',
+            available: true,
+            version: 'test',
+            models: [{ id: 'default', label: 'Default' }],
+          },
+        ],
+      },
+    });
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+async function waitForLoadingToClear(page: Page): Promise<void> {
+  await page
+    .getByText('Loading Open Design…')
+    .waitFor({ state: 'detached', timeout: 15_000 })
+    .catch(() => {});
+}
+
+async function gotoEntryHome(page: Page): Promise<void> {
+  await page.goto('/', { waitUntil: 'domcontentloaded' });
+  await waitForLoadingToClear(page);
+  const privacyDialog = page
+    .getByRole('dialog')
+    .filter({ hasText: 'Help us improve Open Design' });
+  if (await privacyDialog.isVisible().catch(() => false)) {
+    await privacyDialog.getByRole('button', { name: /not now/i }).click();
+    await expect(privacyDialog).toHaveCount(0);
+  }
+  await expect(page.getByTestId('home-hero')).toBeVisible();
+  await expect(page.getByTestId('home-hero-input')).toBeVisible();
+}
+
+async function createBlankProject(page: Page, name: string): Promise<string> {
+  await page.getByTestId('entry-nav-new-project').click();
+  await expect(page.getByTestId('new-project-modal')).toBeVisible();
+  await page.getByTestId('new-project-name').fill(name);
+  await page.getByTestId('create-project').click();
+  await waitForLoadingToClear(page);
+  await expect(page).toHaveURL(/\/projects\//);
+  await expect(page.getByTestId('chat-composer')).toBeVisible();
+
+  const url = new URL(page.url());
+  const segments = url.pathname.split('/');
+  const projectId = segments[2];
+  if (!projectId) throw new Error(`could not extract projectId from ${url.pathname}`);
+  return projectId;
+}
+
+async function seedFile(
+  page: Page,
+  projectId: string,
+  name: string,
+  content: string,
+  encoding?: 'base64',
+): Promise<void> {
+  const res = await page.request.post(`/api/projects/${projectId}/files`, {
+    data: { name, content, ...(encoding ? { encoding } : {}) },
+    timeout: 10_000,
+  });
+  expect(res.ok()).toBeTruthy();
+}
+
+function seedTextFile(page: Page, projectId: string, name: string): Promise<void> {
+  return seedFile(page, projectId, name, `# ${name}`);
+}
+
+function seedPngFile(page: Page, projectId: string, name: string): Promise<void> {
+  return seedFile(page, projectId, name, TINY_PNG_B64, 'base64');
+}
+
+async function openDesignFilesTab(page: Page): Promise<void> {
+  await page.getByTestId('design-files-tab').click();
+  // The Design Files panel renders a table once files are present; wait for
+  // the controls row that always appears at the top of the panel.
+  await expect(page.locator('.df-controls-row')).toBeVisible({ timeout: 10_000 });
+}
+
+// Wait until the per-page <select> is present — it only appears when
+// sortedFiles.length > 15 (showListControls = true).
+async function waitForPageSizeSelect(page: Page): Promise<void> {
+  await expect(page.getByTestId('df-page-size-select')).toBeVisible({ timeout: 10_000 });
+}
+
+// Read the view state from localStorage for a given projectId.
+// Returns null when no entry has been written yet.
+async function readStoredViewState(
+  page: Page,
+  projectId: string,
+): Promise<Record<string, unknown> | null> {
+  const raw = await page.evaluate(
+    ([prefix, pid]) => window.localStorage.getItem(prefix + pid) ?? 'null',
+    [VIEW_STATE_KEY_PREFIX, projectId] as [string, string],
+  );
+  return JSON.parse(raw) as Record<string, unknown> | null;
+}
+
+/**
+ * Seeds a project with 17 PNG files and 1 text file, then reloads.
+ * Enough files so showListControls (> 15) fires and the kind-filter button
+ * appears (2 kinds present).
+ */
+async function seedProjectWithFiles(page: Page, projectId: string): Promise<void> {
+  for (let i = 1; i <= 17; i++) {
+    await seedPngFile(page, projectId, `image-${String(i).padStart(2, '0')}.png`);
+  }
+  await seedTextFile(page, projectId, 'notes.txt');
+  await page.reload();
+  await waitForLoadingToClear(page);
+}
+
+/**
+ * Sets non-default view prefs: pageSize=15, sort=name/asc, kindFilter=image.
+ * Precondition: the Design Files tab must be open and the page-size select visible.
+ */
+async function setNonDefaultViewPrefs(page: Page): Promise<void> {
+  // Change pageSize from default 30 to 15
+  const pageSizeSelect = page.getByTestId('df-page-size-select');
+  await pageSizeSelect.selectOption('15');
+  await expect(pageSizeSelect).toHaveValue('15');
+
+  // Change sort from default mtime/desc to name/asc by clicking Name header
+  const nameHeader = page.locator('th.df-th-name button.df-th-btn');
+  await nameHeader.click();
+  await expect(page.locator('th.df-th-name')).toHaveAttribute('aria-sort', 'ascending');
+
+  // Apply kind filter: open the filter popover and check "Image"
+  const filterBtn = page.getByRole('button', { name: /filter by kind/i });
+  await filterBtn.click();
+  const filterPopover = page.getByRole('dialog', { name: /filter by kind/i });
+  await expect(filterPopover).toBeVisible();
+  await filterPopover.getByRole('checkbox', { name: /image/i }).check();
+  // Close the popover
+  await filterBtn.click();
+  await expect(filterPopover).toBeHidden();
+}
+
+/**
+ * Asserts that the non-default prefs set by setNonDefaultViewPrefs are visible.
+ */
+async function assertNonDefaultViewPrefs(page: Page): Promise<void> {
+  await expect(page.getByTestId('df-page-size-select')).toHaveValue('15');
+  await expect(page.locator('th.df-th-name')).toHaveAttribute('aria-sort', 'ascending');
+  await expect(page.getByRole('button', { name: /filter by kind/i })).toContainText(/image/i);
+}
+
+/**
+ * Asserts that the panel shows the default view prefs (as a fresh project would).
+ */
+async function assertDefaultViewPrefs(page: Page): Promise<void> {
+  await expect(page.getByTestId('df-page-size-select')).toHaveValue('30');
+  await expect(page.locator('th.df-th-name')).toHaveAttribute('aria-sort', 'none');
+  await expect(page.locator('th.df-th-time')).toHaveAttribute('aria-sort', 'descending');
+  await expect(page.getByRole('button', { name: /filter by kind/i })).not.toContainText(/image/i);
+}
+
+// ---------------------------------------------------------------------------
+// Scenario (a): Tab-away / tab-back — prefs survive remount
+// ---------------------------------------------------------------------------
+
+test('(a) view prefs survive navigating away to a file tab and back', async ({ page }) => {
+  await gotoEntryHome(page);
+  const projectId = await createBlankProject(page, 'view-state-nav-test');
+  await seedProjectWithFiles(page, projectId);
+
+  await openDesignFilesTab(page);
+  await waitForPageSizeSelect(page);
+  await setNonDefaultViewPrefs(page);
+
+  // Verify the localStorage entry was written
+  const storedAfterChange = await readStoredViewState(page, projectId);
+  expect(storedAfterChange).not.toBeNull();
+  expect(storedAfterChange!.pageSize).toBe(15);
+  expect(storedAfterChange!.sortKey).toBe('name');
+  expect(storedAfterChange!.sortDir).toBe('asc');
+  expect(Array.isArray(storedAfterChange!.kindFilter)).toBe(true);
+  expect((storedAfterChange!.kindFilter as string[]).includes('image')).toBe(true);
+
+  // Navigate AWAY: open image-01.png in its own tab
+  const firstImageRow = page.getByTestId('design-file-row-image-01.png');
+  await firstImageRow.getByRole('button').first().click();
+  await page.getByTestId('design-file-preview').getByRole('button', { name: 'Open' }).click();
+  const navAwayTab = page.getByRole('tab', { name: /image-01\.png/i });
+  await expect(navAwayTab).toBeVisible();
+  await expect(page.getByTestId('design-files-tab')).toHaveAttribute('aria-selected', 'false');
+
+  // Navigate BACK — remounts DesignFilesPanel
+  await openDesignFilesTab(page);
+  await waitForPageSizeSelect(page);
+
+  // All four prefs must survive the remount
+  await assertNonDefaultViewPrefs(page);
+});
+
+// ---------------------------------------------------------------------------
+// Scenario (b): Hard reload — prefs survive page.reload()
+// ---------------------------------------------------------------------------
+
+test('(b) view prefs survive a hard browser reload', async ({ page }) => {
+  await gotoEntryHome(page);
+  const projectId = await createBlankProject(page, 'view-state-reload-test');
+  await seedProjectWithFiles(page, projectId);
+
+  await openDesignFilesTab(page);
+  await waitForPageSizeSelect(page);
+  await setNonDefaultViewPrefs(page);
+
+  // Hard reload
+  await page.reload();
+  await waitForLoadingToClear(page);
+  await openDesignFilesTab(page);
+  await waitForPageSizeSelect(page);
+
+  // All four prefs must survive the reload
+  await assertNonDefaultViewPrefs(page);
+
+  // The localStorage key must still be intact
+  const storedAfterReload = await readStoredViewState(page, projectId);
+  expect(storedAfterReload).not.toBeNull();
+  expect(storedAfterReload!.pageSize).toBe(15);
+  expect(storedAfterReload!.sortKey).toBe('name');
+  expect(storedAfterReload!.sortDir).toBe('asc');
+  expect((storedAfterReload!.kindFilter as string[]).includes('image')).toBe(true);
+});
+
+// ---------------------------------------------------------------------------
+// Scenario (c): Per-project key isolation — second project shows defaults
+// ---------------------------------------------------------------------------
+
+test('(c) second project view state is independent of the first project', async ({ page }) => {
+  // --- Project A: set non-default prefs ---
+  await gotoEntryHome(page);
+  const projectAId = await createBlankProject(page, 'view-state-project-a');
+  await seedProjectWithFiles(page, projectAId);
+
+  await openDesignFilesTab(page);
+  await waitForPageSizeSelect(page);
+  await setNonDefaultViewPrefs(page);
+
+  // Confirm project A's state was written to localStorage
+  const storedA = await readStoredViewState(page, projectAId);
+  expect(storedA).not.toBeNull();
+  expect(storedA!.pageSize).toBe(15);
+
+  // --- Project B: create, seed, assert defaults ---
+  await gotoEntryHome(page);
+  const projectBId = await createBlankProject(page, 'view-state-project-b');
+
+  // Seed enough files that showListControls fires in project B as well.
+  // Use text files so the kind-filter button appears (2 kinds: text + png).
+  for (let i = 1; i <= 17; i++) {
+    await seedTextFile(page, projectBId, `doc-${String(i).padStart(2, '0')}.txt`);
+  }
+  await seedPngFile(page, projectBId, 'icon.png');
+
+  await page.reload();
+  await waitForLoadingToClear(page);
+  await openDesignFilesTab(page);
+  await waitForPageSizeSelect(page);
+
+  // Project B must show defaults, not project A's persisted prefs
+  await assertDefaultViewPrefs(page);
+
+  // The per-project key for project B, if it exists at all, must NOT contain
+  // values inherited from project A. A default-value entry is acceptable.
+  const storedB = await readStoredViewState(page, projectBId);
+  if (storedB !== null) {
+    expect(storedB.pageSize).not.toBe(15);
+    expect(storedB.sortKey).not.toBe('name');
+    const kf = storedB.kindFilter;
+    if (Array.isArray(kf)) {
+      expect((kf as string[]).includes('image')).toBe(false);
+    }
+  }
+});