diff --git a/client/src/Providers/__tests__/themeCache.spec.ts b/client/src/Providers/__tests__/themeCache.spec.ts
index e1e0bc951fb..3bbe8828991 100644
--- a/client/src/Providers/__tests__/themeCache.spec.ts
+++ b/client/src/Providers/__tests__/themeCache.spec.ts
@@ -1,5 +1,17 @@
-import { clickHouseTheme } from '@librechat/client';
-import { themeRoleFingerprint } from 'librechat-data-provider';
+import {
+  THEME_VERSION,
+  themeRoleFingerprint,
+  themeAppearanceTokens,
+} from 'librechat-data-provider';
+import {
+  themeBrandTokens,
+  themeColorTokens,
+  resolveTheme,
+  libreChatTheme,
+  clickHouseTheme,
+  validateThemeDefinition,
+} from '@librechat/client';
+import type { ThemeDefinition, ResolvedThemeStyle } from '@librechat/client';
 import type { ThemeCacheEntry } from '../themeCache';
 import {
   themeOwner,
@@ -153,3 +165,287 @@ describe('theme cache storage', () => {
     expect(localStorage.getItem(THEME_CACHE_KEY)).toBeNull();
   });
 });
+
+/**
+ * The baseline the cache's persisted output is pinned to. The cache version keys on the role set
+ * and a hand-bumped `THEME_CACHE_EPOCH`, so a release that changes what a cacheable theme
+ * resolves to without adding a role would replay stale styling at boot. The digest covers what
+ * the cache persists (`buildThemeCache(...).modes`, with the property order canonicalized) for
+ * `librechat` and `clickhouse`, the definitions that can enter the cache (the boot script never
+ * replays one under high contrast), and for generated definitions:
+ * - every color, brand and appearance role overridden alone, theme-wide, in light only and in
+ *   dark only (the other mode absent), plus a `none` sample for each shadow-like role;
+ * - every role the resolver derives from others, found by diffing its resolved output against the
+ *   bare theme, with all of its sources named together and again with the role named as well, theme-wide and per mode, so
+ *   fallback precedence and opting out are covered without listing the chains by hand;
+ * - every brand set theme-wide, in light and in dark with conflicting values;
+ * - definitions with one or both mode blocks absent.
+ * A new role, or a new fallback, joins by construction.
+ */
+const PIN = { fingerprint: '1.2.leqd1k', digest: '1fm6x5m' };
+
+const digestOf = (text: string): string => {
+  let hash = 5381;
+  for (let i = 0; i < text.length; i++) {
+    hash = ((hash * 33) ^ text.charCodeAt(i)) >>> 0;
+  }
+  return hash.toString(36);
+};
+
+/** Locale-independent, so the digest does not depend on the collation Jest runs under. */
+const byCodePoint = (a: string, b: string): number => (a < b ? -1 : Number(a > b));
+
+const APPEARANCE_CANDIDATES = [
+  '0.5rem',
+  '1.25rem',
+  'soft',
+  'dim',
+  'fill',
+  '600',
+  '0.5',
+  '150ms',
+  '9rem',
+  '0 1px 2px 0 rgb(0 0 0 / 0.2)',
+  'ui-sans-serif, sans-serif',
+  '1.5',
+  'ring',
+  'border',
+  'none',
+];
+
+type Scope = 'both' | 'light' | 'dark';
+type Mode = 'light' | 'dark';
+type Overrides = {
+  colors?: Record<string, string>;
+  appearance?: Record<string, string>;
+  brands?: Record<string, string>;
+};
+type Fixture = { key: string; theme: ThemeDefinition };
+
+const SCOPES: Scope[] = ['both', 'light', 'dark'];
+const MODES: Mode[] = ['light', 'dark'];
+const COLOR_SENTINEL: Record<Mode, (index: number) => string> = {
+  light: (index) => `${10 + index} 20 30`,
+  dark: (index) => `${200 - index} 210 220`,
+};
+
+/** A definition whose inactive mode block is absent, not empty. */
+const define = (
+  name: string,
+  overrides: (mode: Mode) => Overrides,
+  scope: Scope,
+  wideBrands?: Record<string, string>,
+): ThemeDefinition =>
+  ({
+    version: THEME_VERSION,
+    name,
+    ...(wideBrands && { brands: wideBrands }),
+    modes: Object.fromEntries(
+      MODES.filter((mode) => scope === 'both' || scope === mode).map((mode) => [
+        mode,
+        overrides(mode),
+      ]),
+    ),
+  }) as ThemeDefinition;
+
+const BARE = define('bare', () => ({}), 'both');
+const isValid = (theme: ThemeDefinition): boolean => validateThemeDefinition(theme).length === 0;
+
+/** Every candidate the validator accepts for each appearance role, pinned so a narrowing or widening shows. */
+const ACCEPTED: Record<string, string[]> = Object.fromEntries(
+  themeAppearanceTokens.map((token) => [
+    token,
+    APPEARANCE_CANDIDATES.filter((value) =>
+      isValid(define(token, () => ({ appearance: { [token]: value } }), 'both')),
+    ),
+  ]),
+);
+
+/** The first sample the validator accepts for an appearance role, and `none` when it takes it. */
+function appearanceSamples(token: string): string[] {
+  const accepted = ACCEPTED[token];
+  if (accepted.length === 0) {
+    throw new Error(`Add a valid sample for the appearance role ${token} to APPEARANCE_CANDIDATES`);
+  }
+  return [...new Set([accepted[0], ...accepted.filter((value) => value === 'none')])];
+}
+
+const SAMPLES = Object.fromEntries(
+  themeAppearanceTokens.map((token) => [token, appearanceSamples(token)]),
+);
+
+const colorOverrides = (tokens: readonly string[], mode: Mode): Record<string, string> =>
+  Object.fromEntries(tokens.map((token, index) => [token, COLOR_SENTINEL[mode](index)]));
+
+const appearanceOverrides = (tokens: readonly string[]): Record<string, string> =>
+  Object.fromEntries(tokens.map((token) => [token, SAMPLES[token][0]]));
+
+/** Role to the roles whose single override changes it, read from the resolver. */
+function derivedRoles(): { colors: Map<string, string[]>; appearance: Map<string, string[]> } {
+  const base = MODES.map((mode) => resolveTheme(BARE, mode));
+  const found = {
+    colors: new Map<string, Set<string>>(),
+    appearance: new Map<string, Set<string>>(),
+  };
+  const note = (kind: 'colors' | 'appearance', source: string, theme: ThemeDefinition) =>
+    MODES.forEach((mode, index) => {
+      const resolved = resolveTheme(theme, mode);
+      const before = base[index][kind] as Record<string, unknown>;
+      const after = resolved[kind] as Record<string, unknown>;
+      Object.keys(after)
+        .filter((key) => key !== source && after[key] !== before[key])
+        .forEach((key) => found[kind].set(key, (found[kind].get(key) ?? new Set()).add(source)));
+    });
+  themeColorTokens.forEach((token) =>
+    note(
+      'colors',
+      token,
+      define(token, (mode) => ({ colors: colorOverrides([token], mode) }), 'both'),
+    ),
+  );
+  themeAppearanceTokens.forEach((token) =>
+    note(
+      'appearance',
+      token,
+      define(token, () => ({ appearance: appearanceOverrides([token]) }), 'both'),
+    ),
+  );
+  const sorted = (map: Map<string, Set<string>>) =>
+    new Map([...map].map(([key, sources]) => [key, [...sources].sort()] as [string, string[]]));
+  return { colors: sorted(found.colors), appearance: sorted(found.appearance) };
+}
+
+function roleFixtures(): Fixture[] {
+  const colors = themeColorTokens.flatMap((token) =>
+    SCOPES.map((scope) => ({
+      key: `color:${token}:${scope}`,
+      theme: define(token, (mode) => ({ colors: colorOverrides([token], mode) }), scope),
+    })),
+  );
+  const brands = themeBrandTokens.flatMap((token) => [
+    {
+      key: `brand:${token}:wide`,
+      theme: define(token, () => ({}), 'both', { [token]: '#123456' }),
+    },
+    ...MODES.map((mode) => ({
+      key: `brand:${token}:${mode}`,
+      theme: define(token, () => ({ brands: { [token]: '#123456' } }), mode),
+    })),
+    {
+      key: `brand:${token}:conflict`,
+      theme: define(
+        token,
+        (mode) => ({ brands: { [token]: mode === 'light' ? '#aa0000' : '#00aa00' } }),
+        'both',
+        { [token]: '#0000aa' },
+      ),
+    },
+  ]);
+  const appearance = themeAppearanceTokens.flatMap((token) =>
+    SAMPLES[token].flatMap((value, index) =>
+      SCOPES.map((scope) => ({
+        key: `appearance:${token}:${index}:${scope}`,
+        theme: define(token, () => ({ appearance: { [token]: value } }), scope),
+      })),
+    ),
+  );
+  return [...colors, ...brands, ...appearance];
+}
+
+/** Each derived role with all of its sources named together, then with the role named as well. */
+function derivedFixtures(): Fixture[] {
+  const { colors, appearance } = derivedRoles();
+  const fixtures = (
+    kind: 'color' | 'appearance',
+    chains: Map<string, string[]>,
+    overrides: (tokens: string[], mode: Mode) => Overrides,
+  ) =>
+    [...chains].flatMap(([target, sources]) =>
+      SCOPES.flatMap((scope) => [
+        {
+          key: `derived:${kind}:${target}:sources:${scope}`,
+          theme: define(target, (mode) => overrides(sources, mode), scope),
+        },
+        {
+          key: `derived:${kind}:${target}:named:${scope}`,
+          theme: define(target, (mode) => overrides([...sources, target], mode), scope),
+        },
+      ]),
+    );
+  return [
+    ...fixtures('color', colors, (tokens, mode) => ({ colors: colorOverrides(tokens, mode) })),
+    ...fixtures('appearance', appearance, (tokens) => ({
+      appearance: appearanceOverrides(tokens),
+    })),
+  ];
+}
+
+/** Mode blocks that are missing or empty, on a bare theme and on a bundled one. */
+function modeFixtures(): Fixture[] {
+  const without = (theme: ThemeDefinition, mode: Mode): ThemeDefinition => {
+    const modes = { ...theme.modes };
+    delete modes[mode];
+    return { ...theme, modes };
+  };
+  return [
+    { key: 'modes:none', theme: { version: THEME_VERSION, name: 'none', modes: {} } },
+    { key: 'modes:empty', theme: define('empty', () => ({}), 'both') },
+    { key: 'modes:clickhouse:no-light', theme: without(clickHouseTheme, 'light') },
+    { key: 'modes:clickhouse:no-dark', theme: without(clickHouseTheme, 'dark') },
+  ];
+}
+
+/** Property order is positional in the cache entry and means nothing to the page. */
+const canonical = ({ properties, attributes }: ResolvedThemeStyle) => ({
+  properties: [...properties].sort(([a], [b]) => byCodePoint(a, b)),
+  attributes: Object.fromEntries(Object.entries(attributes).sort(([a], [b]) => byCodePoint(a, b))),
+});
+
+const persistedOutput = () => {
+  const fixtures: Fixture[] = [
+    { key: 'a:librechat', theme: libreChatTheme },
+    { key: 'a:clickhouse', theme: clickHouseTheme },
+    ...roleFixtures(),
+    ...derivedFixtures(),
+    ...modeFixtures(),
+  ].sort((a, b) => byCodePoint(a.key, b.key));
+  return fixtures.map(({ key, theme }) => {
+    const { light, dark } = buildThemeCache(OWNER, key, theme).modes;
+    return [key, canonical(light), canonical(dark)];
+  });
+};
+
+/** What the contributor has to do, or an empty string when the pin is current. */
+function pinStatus(actual: typeof PIN): string {
+  const refreshed = JSON.stringify(actual);
+  if (actual.fingerprint !== PIN.fingerprint) {
+    return `The cache version changed (role set, theme version or epoch), which already retires cached entries: set PIN to ${refreshed}.`;
+  }
+  if (actual.digest !== PIN.digest) {
+    return `The persisted output or the accepted appearance values changed without a version change: bump THEME_CACHE_EPOCH in packages/data-provider/src/theme.ts, then set PIN to the refreshed fingerprint and digest (digest ${actual.digest}).`;
+  }
+  return '';
+}
+
+describe('resolver output pin', () => {
+  it('matches the persisted output of every cacheable definition and generated fixture', () => {
+    const status = pinStatus({
+      fingerprint: themeRoleFingerprint(),
+      digest: digestOf(JSON.stringify({ accepted: ACCEPTED, output: persistedOutput() })),
+    });
+    expect(status).toBe('');
+  });
+
+  it('finds the fallback chains in the resolver, not in a list', () => {
+    const { colors, appearance } = derivedRoles();
+    expect(colors.get('rgb-surface-code')).toContain('rgb-surface-primary-alt');
+    expect(colors.get('rgb-link-prose')).toContain('rgb-link');
+    expect(appearance.get('menuShadow')).toContain('shadowLg');
+  });
+
+  it('tells a version change from an output change', () => {
+    expect(pinStatus({ ...PIN, fingerprint: 'other' })).toMatch(/cache version changed/);
+    expect(pinStatus({ ...PIN, digest: 'other' })).toMatch(/bump THEME_CACHE_EPOCH/);
+    expect(pinStatus(PIN)).toBe('');
+  });
+});