diff --git a/src/App.test.tsx b/src/App.test.tsx
index b14edf1..b7abbc7 100644
--- a/src/App.test.tsx
+++ b/src/App.test.tsx
@@ -35,6 +35,7 @@ describe("React app dashboard state view", () => {
 
     expect(html).toContain('data-ui-theme-toggle="true"');
     expect(html).toContain('aria-label="Switch to light theme"');
+    expect(html).not.toContain("aria-pressed");
     expect(html).toContain("Dark");
   });
 });
diff --git a/src/App.tsx b/src/App.tsx
index 081d630..99cdc5e 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -93,7 +93,7 @@ export default function App() {
   const [theme, setTheme] = useState<UiTheme>(() => {
     if (typeof window === "undefined") return "dark";
 
-    return resolveInitialUiTheme(window.localStorage);
+    return resolveInitialUiTheme(getThemeStorage());
   });
 
   useEffect(() => {
@@ -113,7 +113,7 @@ export default function App() {
 
   useEffect(() => {
     document.documentElement.dataset.uiTheme = theme;
-    persistUiTheme(theme, window.localStorage);
+    persistUiTheme(theme, getThemeStorage());
   }, [theme]);
 
   useEffect(() => {
@@ -173,3 +173,11 @@ function stateIcon(state: DashboardRuntimeState["state"]): string {
   if (state === "loading") return "mdi:progress-clock";
   return "mdi:tray";
 }
+
+function getThemeStorage(): Storage | undefined {
+  try {
+    return window.localStorage;
+  } catch {
+    return undefined;
+  }
+}
diff --git a/src/lib/ui/components/ThemeToggle.tsx b/src/lib/ui/components/ThemeToggle.tsx
index 46455fc..1c8fb1a 100644
--- a/src/lib/ui/components/ThemeToggle.tsx
+++ b/src/lib/ui/components/ThemeToggle.tsx
@@ -14,7 +14,6 @@ export function ThemeToggle({ theme, onThemeChange }: ThemeToggleProps) {
   return (
     <button
       aria-label={label}
-      aria-pressed={theme === "dark"}
       className="theme-toggle"
       data-ui-theme-toggle="true"
       onClick={() => onThemeChange(nextTheme)}
diff --git a/src/lib/ui/stories/ThemeToggle.stories.tsx b/src/lib/ui/stories/ThemeToggle.stories.tsx
index fb10df2..ffcfeef 100644
--- a/src/lib/ui/stories/ThemeToggle.stories.tsx
+++ b/src/lib/ui/stories/ThemeToggle.stories.tsx
@@ -20,4 +20,9 @@ export const Light: Story = {
   args: {
     theme: "light",
   },
+  parameters: {
+    globals: {
+      theme: "light",
+    },
+  },
 };
diff --git a/src/lib/ui/theme.test.ts b/src/lib/ui/theme.test.ts
index cce56de..8ed3f04 100644
--- a/src/lib/ui/theme.test.ts
+++ b/src/lib/ui/theme.test.ts
@@ -2,6 +2,7 @@ import { describe, expect, test } from "vitest";
 import {
   getNextUiTheme,
   isUiTheme,
+  persistUiTheme,
   resolveInitialUiTheme,
   UI_THEME_STORAGE_KEY,
 } from "./theme";
@@ -25,6 +26,26 @@ describe("UI theme preference", () => {
     expect(resolveInitialUiTheme(storage)).toBe("dark");
   });
 
+  test("falls back when stored preferences cannot be read", () => {
+    const storage = {
+      getItem() {
+        throw new Error("storage blocked");
+      },
+    };
+
+    expect(resolveInitialUiTheme(storage)).toBe("dark");
+  });
+
+  test("ignores persistence failures", () => {
+    const storage = {
+      setItem() {
+        throw new Error("quota exceeded");
+      },
+    };
+
+    expect(() => persistUiTheme("light", storage)).not.toThrow();
+  });
+
   test("detects and toggles supported themes", () => {
     expect(isUiTheme("light")).toBe(true);
     expect(isUiTheme("dark")).toBe(true);
diff --git a/src/lib/ui/theme.ts b/src/lib/ui/theme.ts
index 16a8312..9f48df5 100644
--- a/src/lib/ui/theme.ts
+++ b/src/lib/ui/theme.ts
@@ -22,7 +22,7 @@ export function resolveInitialUiTheme(
   storage?: ReadableThemeStorage | null,
   fallback: UiTheme = "dark",
 ): UiTheme {
-  const stored = readStoredTheme(storage);
+  const stored = safeReadStoredTheme(storage);
 
   return isUiTheme(stored) ? stored : fallback;
 }
@@ -33,12 +33,26 @@ export function persistUiTheme(
 ): void {
   if (!storage) return;
 
-  if ("setItem" in storage) {
-    storage.setItem(UI_THEME_STORAGE_KEY, theme);
-    return;
-  }
+  try {
+    if ("setItem" in storage) {
+      storage.setItem(UI_THEME_STORAGE_KEY, theme);
+      return;
+    }
 
-  storage.set(UI_THEME_STORAGE_KEY, theme);
+    storage.set(UI_THEME_STORAGE_KEY, theme);
+  } catch {
+    // Browser storage may be blocked or quota-constrained.
+  }
+}
+
+function safeReadStoredTheme(
+  storage?: ReadableThemeStorage | null,
+): string | undefined {
+  try {
+    return readStoredTheme(storage);
+  } catch {
+    return undefined;
+  }
 }
 
 function readStoredTheme(
diff --git a/tests/e2e/dashboard.spec.ts b/tests/e2e/dashboard.spec.ts
index 80f1726..7110900 100644
--- a/tests/e2e/dashboard.spec.ts
+++ b/tests/e2e/dashboard.spec.ts
@@ -240,6 +240,24 @@ test.describe("dashboard page QA gate", () => {
     expect(results.violations).toEqual([]);
   });
 
+  test("passes automated accessibility checks in light mode", async ({
+    page,
+  }, testInfo) => {
+    test.skip(testInfo.project.name !== "chromium-desktop");
+
+    await page.goto("/");
+    await waitForDashboardReady(page);
+    await page.getByRole("button", { name: "Switch to light theme" }).click();
+    await expect(page.locator("html")).toHaveAttribute("data-ui-theme", "light");
+
+    const results = await new AxeBuilder({ page }).analyze();
+    expect(results.violations).toEqual([]);
+
+    await expect(page).toHaveScreenshot("dashboard-light-desktop.png", {
+      fullPage: true,
+    });
+  });
+
   test("honors reduced-motion preferences", async ({ page }) => {
     await page.emulateMedia({ reducedMotion: "reduce" });
 
diff --git a/tests/e2e/dashboard.spec.ts-snapshots/dashboard-light-desktop-chromium-desktop-linux.png b/tests/e2e/dashboard.spec.ts-snapshots/dashboard-light-desktop-chromium-desktop-linux.png
new file mode 100644
index 0000000..5b04c30
Binary files /dev/null and b/tests/e2e/dashboard.spec.ts-snapshots/dashboard-light-desktop-chromium-desktop-linux.png differ