diff --git a/.changeset/add-gui-store-api.md b/.changeset/add-gui-store-api.md
new file mode 100644
index 000000000..0bca72941
--- /dev/null
+++ b/.changeset/add-gui-store-api.md
@@ -0,0 +1,7 @@
+---
+"@moonshot-ai/protocol": patch
+"@moonshot-ai/server": patch
+"@moonshot-ai/kimi-code": patch
+---
+
+Add a server-side key-value store API for persisting web UI preferences to the user's data directory.
diff --git a/packages/protocol/src/index.ts b/packages/protocol/src/index.ts
index accd02078..16489267e 100644
--- a/packages/protocol/src/index.ts
+++ b/packages/protocol/src/index.ts
@@ -40,3 +40,4 @@ export * from './rest/modelCatalog';
 export * from './rest/config';
 export * from './rest/terminal';
 export * from './rest/connection';
+export * from './rest/guiStore';
diff --git a/packages/protocol/src/rest/guiStore.ts b/packages/protocol/src/rest/guiStore.ts
new file mode 100644
index 000000000..b7daf1910
--- /dev/null
+++ b/packages/protocol/src/rest/guiStore.ts
@@ -0,0 +1,22 @@
+import { z } from 'zod';
+
+const keySchema = z.string().min(1).max(256);
+
+export const guiStoreGetItemQuerySchema = z.object({ key: keySchema });
+
+export const guiStoreSetItemBodySchema = z.object({
+  key: keySchema,
+  value: z.string(),
+});
+
+export const guiStoreRemoveItemBodySchema = z.object({ key: keySchema });
+
+export const guiStoreGetItemResponseSchema = z.object({
+  value: z.string().nullable(),
+});
+export type GuiStoreGetItemResponse = z.infer<typeof guiStoreGetItemResponseSchema>;
+
+export const guiStoreLengthResponseSchema = z.object({
+  length: z.number(),
+});
+export type GuiStoreLengthResponse = z.infer<typeof guiStoreLengthResponseSchema>;
diff --git a/packages/server/package.json b/packages/server/package.json
index dd65cc98a..7f0aa2088 100644
--- a/packages/server/package.json
+++ b/packages/server/package.json
@@ -19,6 +19,7 @@
     "#/services/approval/*": "./src/services/approval/*.ts",
     "#/services/gateway": "./src/services/gateway/index.ts",
     "#/services/gateway/*": "./src/services/gateway/*.ts",
+    "#/services/guiStore/*": "./src/services/guiStore/*.ts",
     "#/services/question": "./src/services/question/index.ts",
     "#/services/question/*": "./src/services/question/*.ts",
     "#/services/snapshot": "./src/services/snapshot/index.ts",
@@ -46,6 +47,7 @@
     "fastify": "^5.1.0",
     "pino": "^9.5.0",
     "pino-pretty": "^13.0.0",
+    "smol-toml": "^1.6.1",
     "ulid": "^3.0.1",
     "ws": "^8.18.0",
     "zod": "catalog:",
diff --git a/packages/server/src/routes/guiStore.ts b/packages/server/src/routes/guiStore.ts
new file mode 100644
index 000000000..1a93d9e21
--- /dev/null
+++ b/packages/server/src/routes/guiStore.ts
@@ -0,0 +1,146 @@
+import {
+  ErrorCode,
+  guiStoreGetItemQuerySchema,
+  guiStoreGetItemResponseSchema,
+  guiStoreLengthResponseSchema,
+  guiStoreRemoveItemBodySchema,
+  guiStoreSetItemBodySchema,
+} from '@moonshot-ai/protocol';
+import { z } from 'zod';
+import type { IInstantiationService } from '@moonshot-ai/agent-core';
+
+import { IGuiStoreService } from '#/services/guiStore/guiStore';
+
+import { okEnvelope } from '../envelope';
+import { defineRoute } from '../middleware/defineRoute';
+
+interface GuiStoreRouteHost {
+  get(
+    path: string,
+    options: { schema?: Record<string, unknown> },
+    handler: (
+      req: { id: string; query?: unknown },
+      reply: { send(payload: unknown): void },
+    ) => Promise<void> | void,
+  ): unknown;
+  post(
+    path: string,
+    options: { schema?: Record<string, unknown> },
+    handler: (
+      req: { id: string; body?: unknown },
+      reply: { send(payload: unknown): void },
+    ) => Promise<void> | void,
+  ): unknown;
+}
+
+export function registerGuiStoreRoutes(
+  app: GuiStoreRouteHost,
+  ix: IInstantiationService,
+): void {
+  const getItemRoute = defineRoute(
+    {
+      method: 'GET',
+      path: '/gui/store/getItem',
+      querystring: guiStoreGetItemQuerySchema,
+      success: { data: guiStoreGetItemResponseSchema },
+      errors: { [ErrorCode.VALIDATION_FAILED]: {} },
+      description: 'Read a value by key (mirrors localStorage.getItem).',
+      tags: ['gui-store'],
+    },
+    async (req, reply) => {
+      const value = await ix.invokeFunction((a) =>
+        a.get(IGuiStoreService).getItem(req.query.key),
+      );
+      reply.send(okEnvelope({ value }, req.id));
+    },
+  );
+  app.get(
+    getItemRoute.path,
+    getItemRoute.options,
+    getItemRoute.handler as Parameters<GuiStoreRouteHost['get']>[2],
+  );
+
+  const setItemRoute = defineRoute(
+    {
+      method: 'POST',
+      path: '/gui/store/setItem',
+      body: guiStoreSetItemBodySchema,
+      success: { data: z.null() },
+      errors: { [ErrorCode.VALIDATION_FAILED]: {} },
+      description: 'Write a value by key (mirrors localStorage.setItem).',
+      tags: ['gui-store'],
+    },
+    async (req, reply) => {
+      await ix.invokeFunction((a) =>
+        a.get(IGuiStoreService).setItem(req.body.key, req.body.value),
+      );
+      reply.send(okEnvelope(null, req.id));
+    },
+  );
+  app.post(
+    setItemRoute.path,
+    setItemRoute.options,
+    setItemRoute.handler as Parameters<GuiStoreRouteHost['post']>[2],
+  );
+
+  const removeItemRoute = defineRoute(
+    {
+      method: 'POST',
+      path: '/gui/store/removeItem',
+      body: guiStoreRemoveItemBodySchema,
+      success: { data: z.null() },
+      errors: { [ErrorCode.VALIDATION_FAILED]: {} },
+      description: 'Delete a value by key (mirrors localStorage.removeItem).',
+      tags: ['gui-store'],
+    },
+    async (req, reply) => {
+      await ix.invokeFunction((a) =>
+        a.get(IGuiStoreService).removeItem(req.body.key),
+      );
+      reply.send(okEnvelope(null, req.id));
+    },
+  );
+  app.post(
+    removeItemRoute.path,
+    removeItemRoute.options,
+    removeItemRoute.handler as Parameters<GuiStoreRouteHost['post']>[2],
+  );
+
+  const clearRoute = defineRoute(
+    {
+      method: 'POST',
+      path: '/gui/store/clear',
+      success: { data: z.null() },
+      description: 'Delete all values (mirrors localStorage.clear).',
+      tags: ['gui-store'],
+    },
+    async (req, reply) => {
+      await ix.invokeFunction((a) => a.get(IGuiStoreService).clear());
+      reply.send(okEnvelope(null, req.id));
+    },
+  );
+  app.post(
+    clearRoute.path,
+    clearRoute.options,
+    clearRoute.handler as Parameters<GuiStoreRouteHost['post']>[2],
+  );
+
+  const lengthRoute = defineRoute(
+    {
+      method: 'GET',
+      path: '/gui/store/length',
+      success: { data: guiStoreLengthResponseSchema },
+      description: 'Number of stored keys (mirrors localStorage.length).',
+      tags: ['gui-store'],
+    },
+    async (req, reply) => {
+      const length = await ix.invokeFunction((a) => a.get(IGuiStoreService).length());
+      reply.send(okEnvelope({ length }, req.id));
+    },
+  );
+  app.get(
+    lengthRoute.path,
+    lengthRoute.options,
+    lengthRoute.handler as Parameters<GuiStoreRouteHost['get']>[2],
+  );
+}
diff --git a/packages/server/src/routes/registerApiV1Routes.ts b/packages/server/src/routes/registerApiV1Routes.ts
index 38297e5f0..5c3a53c94 100644
--- a/packages/server/src/routes/registerApiV1Routes.ts
+++ b/packages/server/src/routes/registerApiV1Routes.ts
@@ -9,6 +9,7 @@ import { registerConnectionsRoutes } from './connections';
 import { registerDebugRoutes } from './debug';
 import { registerFilesRoutes } from './files';
 import { registerFsRoutes } from './fs';
+import { registerGuiStoreRoutes } from './guiStore';
 import { registerMessagesRoutes } from './messages';
 import { registerMetaRoute } from './meta';
 import { registerModelCatalogRoutes } from './modelCatalog';
@@ -114,6 +115,7 @@ export async function registerApiV1Routes(
       );
     }
     registerFsRoutes(apiV1 as unknown as Parameters<typeof registerFsRoutes>[0], ix);
+    registerGuiStoreRoutes(apiV1 as unknown as Parameters<typeof registerGuiStoreRoutes>[0], ix);
     registerFilesRoutes(apiV1 as unknown as Parameters<typeof registerFilesRoutes>[0], ix);
     registerWorkspacesRoutes(
       apiV1 as unknown as Parameters<typeof registerWorkspacesRoutes>[0],
diff --git a/packages/server/src/services/guiStore/guiStore.ts b/packages/server/src/services/guiStore/guiStore.ts
new file mode 100644
index 000000000..c6d9e936e
--- /dev/null
+++ b/packages/server/src/services/guiStore/guiStore.ts
@@ -0,0 +1,18 @@
+import { createDecorator } from '@moonshot-ai/agent-core';
+
+/**
+ * `IGuiStoreService` — a server-backed key/value store mirroring the browser
+ * `localStorage` interface (`getItem` / `setItem` / `removeItem` / `clear` /
+ * `length`). Values are opaque strings; callers (the web UI) handle their own
+ * serialization. Persisted to `<homeDir>/gui.toml`.
+ */
+export interface IGuiStoreService {
+  readonly _serviceBrand: undefined;
+  getItem(key: string): Promise<string | null>;
+  setItem(key: string, value: string): Promise<void>;
+  removeItem(key: string): Promise<void>;
+  clear(): Promise<void>;
+  length(): Promise<number>;
+}
+
+export const IGuiStoreService = createDecorator<IGuiStoreService>('guiStoreService');
diff --git a/packages/server/src/services/guiStore/guiStoreService.ts b/packages/server/src/services/guiStore/guiStoreService.ts
new file mode 100644
index 000000000..3a3732eac
--- /dev/null
+++ b/packages/server/src/services/guiStore/guiStoreService.ts
@@ -0,0 +1,110 @@
+import { randomBytes } from 'node:crypto';
+import { mkdir, readFile, rename, writeFile } from 'node:fs/promises';
+import { dirname, join } from 'node:path';
+
+import { IEnvironmentService } from '@moonshot-ai/agent-core';
+import { parse as parseToml, stringify as stringifyToml } from 'smol-toml';
+
+import { IGuiStoreService } from './guiStore';
+
+/**
+ * Null-prototype record so keys present on `Object.prototype` (`toString`,
+ * `constructor`, `hasOwnProperty`, `__proto__`, …) never resolve to inherited
+ * members — they are legal localStorage keys and must behave like any other key.
+ */
+function emptyStore(): Record<string, string> {
+  return Object.create(null) as Record<string, string>;
+}
+
+export class GuiStoreService implements IGuiStoreService {
+  readonly _serviceBrand: undefined;
+
+  private readonly filePath: string;
+  /** Serializes read-modify-write cycles so concurrent writers cannot clobber each other. */
+  private queue: Promise<void> = Promise.resolve();
+
+  constructor(@IEnvironmentService env: IEnvironmentService) {
+    this.filePath = join(env.homeDir, 'gui.toml');
+  }
+
+  async getItem(key: string): Promise<string | null> {
+    const all = await this.readAll();
+    if (!Object.prototype.hasOwnProperty.call(all, key)) return null;
+    return all[key] ?? null;
+  }
+
+  async setItem(key: string, value: string): Promise<void> {
+    await this.withLock(async () => {
+      const all = await this.readAll();
+      all[key] = value;
+      await this.writeAll(all);
+    });
+  }
+
+  async removeItem(key: string): Promise<void> {
+    await this.withLock(async () => {
+      const all = await this.readAll();
+      if (Object.prototype.hasOwnProperty.call(all, key)) {
+        delete all[key];
+        await this.writeAll(all);
+      }
+    });
+  }
+
+  async clear(): Promise<void> {
+    await this.withLock(() => this.writeAll(emptyStore()));
+  }
+
+  async length(): Promise<number> {
+    const all = await this.readAll();
+    return Object.keys(all).length;
+  }
+
+  private withLock(fn: () => Promise<void>): Promise<void> {
+    const run = this.queue.then(fn);
+    // Keep the chain alive regardless of outcome; the rejection is still
+    // surfaced to the caller of this specific operation via `run`.
+    this.queue = run.then(
+      () => undefined,
+      () => undefined,
+    );
+    return run;
+  }
+
+  private async readAll(): Promise<Record<string, string>> {
+    let text: string;
+    try {
+      text = await readFile(this.filePath, 'utf-8');
+    } catch (error) {
+      if ((error as NodeJS.ErrnoException).code === 'ENOENT') return emptyStore();
+      throw error;
+    }
+    if (text.trim().length === 0) return emptyStore();
+    try {
+      const parsed = parseToml(text) as Record<string, unknown>;
+      const out = emptyStore();
+      for (const [k, v] of Object.entries(parsed)) {
+        if (typeof v === 'string') out[k] = v;
+      }
+      return out;
+    } catch {
+      // A corrupt or partially-written file must not take down the store;
+      // treat it as empty. The next write replaces it with valid TOML.
+      return emptyStore();
+    }
+  }
+
+  private async writeAll(obj: Record<string, string>): Promise<void> {
+    await mkdir(dirname(this.filePath), { recursive: true, mode: 0o700 });
+    // Spread into a plain object so smol-toml never touches a null-prototype object.
+    const plain: Record<string, string> = { ...obj };
+    const text = Object.keys(plain).length === 0 ? '' : stringifyToml(plain);
+    // Atomic replace via temp file + rename (POSIX-atomic), so readers never
+    // observe a half-written file.
+    const tmp = `${this.filePath}.tmp.${process.pid}.${randomBytes(4).toString('hex')}`;
+    // 0600: the store can hold unsent drafts / input history; keep it private
+    // to the owning user on multi-user hosts.
+    await writeFile(tmp, text, { encoding: 'utf-8', mode: 0o600 });
+    await rename(tmp, this.filePath);
+  }
+}
diff --git a/packages/server/src/services/serviceCollection.ts b/packages/server/src/services/serviceCollection.ts
index 0ffdc8ed9..fb5486b41 100644
--- a/packages/server/src/services/serviceCollection.ts
+++ b/packages/server/src/services/serviceCollection.ts
@@ -27,6 +27,8 @@ import {
   ModelCatalogRefreshScheduler,
 } from '#/services/modelCatalog/modelCatalogRefreshScheduler';
 import { ISnapshotService, SnapshotService, loadSnapshotConfig } from '#/services/snapshot';
+import { IGuiStoreService } from '#/services/guiStore/guiStore';
+import { GuiStoreService } from '#/services/guiStore/guiStoreService';
 
 export interface ServerServiceCollectionOptions {
   readonly server: ServerStartOptions;
@@ -67,6 +69,7 @@ export function createServerServiceCollection(
   );
   services.set(IRestGateway, new FastifyRestGateway(app));
   services.set(Services.IEnvironmentService, envService);
+  services.set(IGuiStoreService, new SyncDescriptor(GuiStoreService, [], false));
 
   services.set(
     IWSGateway,
diff --git a/packages/server/test/__snapshots__/api-surface.snapshot.test.ts.snap b/packages/server/test/__snapshots__/api-surface.snapshot.test.ts.snap
index 2ad3980b2..df69bdedc 100644
--- a/packages/server/test/__snapshots__/api-surface.snapshot.test.ts.snap
+++ b/packages/server/test/__snapshots__/api-surface.snapshot.test.ts.snap
@@ -61,6 +61,14 @@ exports[`API surface snapshot > matches the documented v1 route table and meta e
       "GET",
       "/api/v1/fs:home",
     ],
+    [
+      "GET",
+      "/api/v1/gui/store/getItem",
+    ],
+    [
+      "GET",
+      "/api/v1/gui/store/length",
+    ],
     [
       "GET",
       "/api/v1/healthz",
@@ -189,6 +197,18 @@ exports[`API surface snapshot > matches the documented v1 route table and meta e
       "POST",
       "/api/v1/files",
     ],
+    [
+      "POST",
+      "/api/v1/gui/store/clear",
+    ],
+    [
+      "POST",
+      "/api/v1/gui/store/removeItem",
+    ],
+    [
+      "POST",
+      "/api/v1/gui/store/setItem",
+    ],
     [
       "POST",
       "/api/v1/mcp/servers/{tail}",
diff --git a/packages/server/test/guiStore.e2e.test.ts b/packages/server/test/guiStore.e2e.test.ts
new file mode 100644
index 000000000..dc4a847e8
--- /dev/null
+++ b/packages/server/test/guiStore.e2e.test.ts
@@ -0,0 +1,223 @@
+import { mkdtempSync, readFileSync, rmSync, statSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+import { pino } from 'pino';
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+import { IRestGateway, startServer, type RunningServer } from '../src';
+import { fixedTokenAuth } from './helpers/serverHarness';
+
+let tmpDir: string;
+let lockPath: string;
+let bridgeHome: string;
+let server: RunningServer | undefined;
+
+beforeEach(() => {
+  tmpDir = mkdtempSync(join(tmpdir(), 'kimi-server-gui-store-test-'));
+  lockPath = join(tmpDir, 'lock');
+  bridgeHome = mkdtempSync(join(tmpdir(), 'kimi-server-gui-store-home-'));
+});
+
+afterEach(async () => {
+  try {
+    await server?.close();
+  } catch {
+    // ignore
+  }
+  server = undefined;
+  rmSync(tmpDir, { recursive: true, force: true });
+  rmSync(bridgeHome, { recursive: true, force: true });
+});
+
+async function bootDaemon(): Promise<RunningServer> {
+  server = await startServer({
+    serviceOverrides: [fixedTokenAuth()],
+    host: '127.0.0.1',
+    port: 0,
+    lockPath,
+    logger: pino({ level: 'silent' }),
+    coreProcessOptions: { homeDir: bridgeHome },
+  });
+  return server;
+}
+
+function appOf(r: RunningServer): {
+  inject: (req: unknown) => Promise<{ statusCode: number; json: () => unknown }>;
+} {
+  const app = r.services.invokeFunction((a) => {
+    const gw = a.get(IRestGateway);
+    return gw.app as unknown as {
+      inject: (req: unknown) => Promise<{ statusCode: number; json: () => unknown }>;
+    };
+  });
+  return {
+    inject(req: unknown) {
+      const q = req as { headers?: Record<string, string | string[] | undefined> };
+      return app.inject({
+        ...q,
+        headers: { authorization: 'Bearer test-token', ...q.headers },
+      });
+    },
+  };
+}
+
+function envelopeOf<T>(body: unknown): {
+  code: number;
+  msg: string;
+  data: T | null;
+  request_id: string;
+} {
+  return body as {
+    code: number;
+    msg: string;
+    data: T | null;
+    request_id: string;
+  };
+}
+
+function getItem(api: ReturnType<typeof appOf>, key: string) {
+  return api.inject({ method: 'GET', url: `/api/v1/gui/store/getItem?key=${key}` });
+}
+
+function setItem(api: ReturnType<typeof appOf>, key: string, value: string) {
+  return api.inject({
+    method: 'POST',
+    url: '/api/v1/gui/store/setItem',
+    payload: { key, value },
+  });
+}
+
+describe('gui store routes', () => {
+  it('getItem returns null when the file does not exist', async () => {
+    const r = await bootDaemon();
+    const res = await getItem(appOf(r), 'theme');
+    expect(res.statusCode).toBe(200);
+    const env = envelopeOf<{ value: string | null }>(res.json());
+    expect(env.code).toBe(0);
+    expect(env.data?.value).toBeNull();
+  });
+
+  it('setItem then getItem round-trips and persists to gui.toml', async () => {
+    const r = await bootDaemon();
+    const api = appOf(r);
+
+    const setRes = await setItem(api, 'theme', 'modern');
+    expect(envelopeOf<null>(setRes.json()).code).toBe(0);
+
+    const getEnv = envelopeOf<{ value: string | null }>((await getItem(api, 'theme')).json());
+    expect(getEnv.data?.value).toBe('modern');
+
+    const text = readFileSync(join(bridgeHome, 'gui.toml'), 'utf-8');
+    expect(text).toContain('theme = "modern"');
+  });
+
+  it('setItem overwrites an existing value', async () => {
+    const r = await bootDaemon();
+    const api = appOf(r);
+    await setItem(api, 'theme', 'modern');
+    await setItem(api, 'theme', 'terminal');
+
+    const env = envelopeOf<{ value: string | null }>((await getItem(api, 'theme')).json());
+    expect(env.data?.value).toBe('terminal');
+  });
+
+  it('removeItem deletes a key and leaves others intact', async () => {
+    const r = await bootDaemon();
+    const api = appOf(r);
+    await setItem(api, 'a', '1');
+    await setItem(api, 'b', '2');
+    const rmRes = await api.inject({
+      method: 'POST',
+      url: '/api/v1/gui/store/removeItem',
+      payload: { key: 'a' },
+    });
+    expect(envelopeOf<null>(rmRes.json()).code).toBe(0);
+
+    expect(envelopeOf<{ value: string | null }>((await getItem(api, 'a')).json()).data?.value).toBeNull();
+    expect(envelopeOf<{ value: string | null }>((await getItem(api, 'b')).json()).data?.value).toBe('2');
+  });
+
+  it('removeItem on a missing key is a no-op', async () => {
+    const r = await bootDaemon();
+    const res = await appOf(r).inject({
+      method: 'POST',
+      url: '/api/v1/gui/store/removeItem',
+      payload: { key: 'nope' },
+    });
+    expect(envelopeOf<null>(res.json()).code).toBe(0);
+  });
+
+  it('length reports the count and clear empties the store', async () => {
+    const r = await bootDaemon();
+    const api = appOf(r);
+    await setItem(api, 'a', '1');
+    await setItem(api, 'b', '2');
+
+    const before = envelopeOf<{ length: number }>(
+      (await api.inject({ method: 'GET', url: '/api/v1/gui/store/length' })).json(),
+    );
+    expect(before.data?.length).toBe(2);
+
+    const clearRes = await api.inject({ method: 'POST', url: '/api/v1/gui/store/clear' });
+    expect(envelopeOf<null>(clearRes.json()).code).toBe(0);
+
+    const after = envelopeOf<{ length: number }>(
+      (await api.inject({ method: 'GET', url: '/api/v1/gui/store/length' })).json(),
+    );
+    expect(after.data?.length).toBe(0);
+  });
+
+  it('quotes dotted keys in the persisted TOML and reads them back', async () => {
+    const r = await bootDaemon();
+    const api = appOf(r);
+    await setItem(api, 'kimi-web.theme', 'modern');
+
+    const text = readFileSync(join(bridgeHome, 'gui.toml'), 'utf-8');
+    expect(text).toContain('"kimi-web.theme" = "modern"');
+
+    const env = envelopeOf<{ value: string | null }>((await getItem(api, 'kimi-web.theme')).json());
+    expect(env.data?.value).toBe('modern');
+  });
+
+  it('rejects an empty key', async () => {
+    const r = await bootDaemon();
+    const res = await appOf(r).inject({
+      method: 'POST',
+      url: '/api/v1/gui/store/setItem',
+      payload: { key: '', value: 'x' },
+    });
+    expect(envelopeOf(res.json()).code).toBe(40001);
+  });
+
+  it('treats Object.prototype keys as ordinary keys', async () => {
+    const r = await bootDaemon();
+    const api = appOf(r);
+
+    // On an empty store, prototype keys must not resolve to inherited members.
+    expect(
+      envelopeOf<{ value: string | null }>((await getItem(api, 'toString')).json()).data?.value,
+    ).toBeNull();
+    expect(
+      envelopeOf<{ value: string | null }>((await getItem(api, 'constructor')).json()).data?.value,
+    ).toBeNull();
+
+    // They can be set and read back like any other key, including __proto__.
+    await setItem(api, 'hasOwnProperty', 'x');
+    await setItem(api, '__proto__', 'y');
+    expect(
+      envelopeOf<{ value: string | null }>((await getItem(api, 'hasOwnProperty')).json()).data
+        ?.value,
+    ).toBe('x');
+    expect(
+      envelopeOf<{ value: string | null }>((await getItem(api, '__proto__')).json()).data?.value,
+    ).toBe('y');
+  });
+
+  it('writes gui.toml with 0600 permissions', async () => {
+    const r = await bootDaemon();
+    await setItem(appOf(r), 'theme', 'modern');
+    const mode = statSync(join(bridgeHome, 'gui.toml')).mode & 0o777;
+    expect(mode).toBe(0o600);
+  });
+});
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 62e201ac4..245b39318 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -580,6 +580,9 @@ importers:
       pino-pretty:
         specifier: ^13.0.0
         version: 13.1.3
+      smol-toml:
+        specifier: ^1.6.1
+        version: 1.6.1
       ulid:
         specifier: ^3.0.1
         version: 3.0.2