fix(themes): guard installed-themes storage against non-array JSON

lib/src/lib/themes/store.test.ts

@@ -0,0 +1,72 @@
+/**
+ * @vitest-environment jsdom
+ */
+import { beforeEach, describe, expect, it } from 'vitest';
+import type { DormouseTheme } from './types';
+import {
+  addInstalledTheme,
+  getAllThemes,
+  getBundledThemes,
+  getInstalledThemes,
+} from './store';
+
+const INSTALLED_KEY = 'dormouse:installed-themes';
+
+function installStorageStub(): void {
+  const values = new Map<string, string>();
+  Object.defineProperty(globalThis, 'localStorage', {
+    configurable: true,
+    value: {
+      clear: () => values.clear(),
+      getItem: (key: string) => values.get(key) ?? null,
+      removeItem: (key: string) => values.delete(key),
+      setItem: (key: string, value: string) => values.set(key, value),
+    },
+  });
+}
+
+function makeInstalledTheme(id: string): DormouseTheme {
+  return {
+    id,
+    label: id,
+    type: 'dark',
+    swatch: '#000000',
+    accent: '#ffffff',
+    vars: {},
+    origin: { kind: 'installed', extensionId: 'pub/ext', installedAt: '2026-07-17' },
+  };
+}
+
+describe('theme store', () => {
+  beforeEach(() => {
+    installStorageStub();
+  });
+
+  it('returns [] when the installed-themes value is valid JSON but not an array', () => {
+    // Corrupted or externally tampered storage: parses fine, wrong shape.
+    localStorage.setItem(INSTALLED_KEY, JSON.stringify({ id: 'oops' }));
+
+    // Regression: before the Array.isArray guard, the object was returned cast
+    // as DormouseTheme[], and getAllThemes()'s spread / addInstalledTheme()'s
+    // filter threw an uncaught TypeError.
+    expect(getInstalledThemes()).toEqual([]);
+    expect(() => getAllThemes()).not.toThrow();
+    expect(getAllThemes()).toEqual(getBundledThemes());
+    expect(() => addInstalledTheme(makeInstalledTheme('recover'))).not.toThrow();
+    expect(getInstalledThemes().map((t) => t.id)).toEqual(['recover']);
+  });
+
+  it('returns [] for non-JSON garbage in storage', () => {
+    localStorage.setItem(INSTALLED_KEY, 'not json at all');
+    expect(getInstalledThemes()).toEqual([]);
+  });
+
+  it('installs a theme and dedupes by id on reinstall', () => {
+    addInstalledTheme(makeInstalledTheme('a'));
+    addInstalledTheme(makeInstalledTheme('b'));
+    expect(getInstalledThemes().map((t) => t.id)).toEqual(['a', 'b']);
+
+    addInstalledTheme(makeInstalledTheme('a'));
+    expect(getInstalledThemes().map((t) => t.id)).toEqual(['b', 'a']);
+  });
+});

lib/src/lib/themes/store.ts

@@ -27,7 +27,13 @@ export function getInstalledThemes(): DormouseTheme[] {
   if (!storage) return [];
   try {
     const raw = storage.getItem(INSTALLED_KEY);
-    return raw ? (JSON.parse(raw) as DormouseTheme[]) : [];
+    if (!raw) return [];
+    // Guard against valid-but-wrong-shaped JSON (corrupted or externally
+    // tampered storage): a non-array value would otherwise be returned cast
+    // as DormouseTheme[], and the later `.filter`/spread callers would throw
+    // an uncaught TypeError that breaks theme listing and installation.
+    const parsed: unknown = JSON.parse(raw);
+    return Array.isArray(parsed) ? (parsed as DormouseTheme[]) : [];
   } catch {
     return [];
   }