diff --git a/server/src/nest/app.module.ts b/server/src/nest/app.module.ts
index 4749f7df4..523df4dba 100644
--- a/server/src/nest/app.module.ts
+++ b/server/src/nest/app.module.ts
@@ -60,6 +60,7 @@ import { ReservationImportModule } from './reservation-import/reservation-import
 import { LlmParseModule } from './llm-parse/llm-parse.module';
 import { AuthModule } from './auth/auth.module';
 import { OidcModule } from './oidc/oidc.module';
+import { NativeAuthModule } from './native-auth/native-auth.module';
 import { OauthModule } from './oauth/oauth.module';
 import { AdminModule } from './admin/admin.module';
 import { AddonsModule } from './addons/addons.module';
@@ -82,7 +83,7 @@ import { RealtimeGatewayModule } from './realtime/realtime-gateway.module';
  * migrated.
  */
 @Module({
-  imports: [AppConfigModule, DatabaseModule, RealtimeModule, RealtimeGatewayModule, SchedulingModule, McpModule.forRoot({ accessPolicy: trekMcpAccessPolicy, validateAccess: trekMcpValidateAccess }), HealthModule, PlatformModule, McpTransportModule, WeatherModule, PublicApiModule, HelpModule, AirportsModule, ConfigModule, SystemNoticesModule, GeoModule, MapsModule, PlaceEnrichmentModule, PlaceShadowModule, RouteUsageModule, CategoriesModule, TagsModule, NotificationsModule, AtlasModule, VacayModule, SchoolHolidaysModule, PackingModule, TodoModule, BudgetModule, ReservationsModule, DaysModule, DayNotesModule, AccommodationsModule, AssignmentsModule, PlacesModule, RoadtripModule, TripsModule, CollabModule, FilesModule, DocSyncModule, PhotosModule, MemoriesModule, AirtrailModule, DawarichModule, JourneyModule, CollectionsModule, ShareModule, TripInviteModule, TransitModule, FeedsModule, SettingsModule, StorageModule, BackupModule, AuthModule, OidcModule, OauthModule, AdminModule, AddonsModule, AuditModule, PermissionsModule, PluginsModule, BookingImportModule, ReservationImportModule, LlmParseModule, ManagedExtModule],
+  imports: [AppConfigModule, DatabaseModule, RealtimeModule, RealtimeGatewayModule, SchedulingModule, McpModule.forRoot({ accessPolicy: trekMcpAccessPolicy, validateAccess: trekMcpValidateAccess }), HealthModule, PlatformModule, McpTransportModule, WeatherModule, PublicApiModule, HelpModule, AirportsModule, ConfigModule, SystemNoticesModule, GeoModule, MapsModule, PlaceEnrichmentModule, PlaceShadowModule, RouteUsageModule, CategoriesModule, TagsModule, NotificationsModule, AtlasModule, VacayModule, SchoolHolidaysModule, PackingModule, TodoModule, BudgetModule, ReservationsModule, DaysModule, DayNotesModule, AccommodationsModule, AssignmentsModule, PlacesModule, RoadtripModule, TripsModule, CollabModule, FilesModule, DocSyncModule, PhotosModule, MemoriesModule, AirtrailModule, DawarichModule, JourneyModule, CollectionsModule, ShareModule, TripInviteModule, TransitModule, FeedsModule, SettingsModule, StorageModule, BackupModule, AuthModule, OidcModule, NativeAuthModule, OauthModule, AdminModule, AddonsModule, AuditModule, PermissionsModule, PluginsModule, BookingImportModule, ReservationImportModule, LlmParseModule, ManagedExtModule],
   providers: [
     // Default-deny: a route is authenticated unless it carries @Public() or
     // @OptionalAuth(), or declares its own @UseGuards chain. Protection used to
diff --git a/server/src/nest/common/validate-route-guards.ts b/server/src/nest/common/validate-route-guards.ts
index f3cf8d96e..2e516e40b 100644
--- a/server/src/nest/common/validate-route-guards.ts
+++ b/server/src/nest/common/validate-route-guards.ts
@@ -139,6 +139,9 @@ export const PUBLIC_ROUTE_ALLOW_LIST: string[] = [
   'McpTransportController.delete',
   'McpTransportController.get',
   'McpTransportController.post',
+  // The native app redeems a one-time code from the system browser here. The
+  // code is only good together with the verifier the app kept to itself.
+  'NativeAuthController.exchange',
   'OauthPublicController.revoke',
   'OauthPublicController.token',
   'OauthPublicController.userinfo',
diff --git a/server/src/nest/health/features.controller.ts b/server/src/nest/health/features.controller.ts
index 9df6b7041..a87061308 100644
--- a/server/src/nest/health/features.controller.ts
+++ b/server/src/nest/health/features.controller.ts
@@ -31,6 +31,10 @@ export class FeaturesController {
       // Addon-level flag (per-user config availability is reported per-file in
       // the preview response). Drives whether the client shows AI affordances.
       aiParsing: this.addons.isAddonEnabled(ADDON_IDS.LLM_PARSING),
+      // The native apps refuse to connect to a server without this: an older
+      // one serves a UI that knows neither the sign-in hand-off nor the way
+      // back to the server picker, and the user would be stuck in it.
+      nativeApp: true,
     };
   }
 }
diff --git a/server/src/nest/native-auth/native-auth.controller.ts b/server/src/nest/native-auth/native-auth.controller.ts
new file mode 100644
index 000000000..34ce85b7d
--- /dev/null
+++ b/server/src/nest/native-auth/native-auth.controller.ts
@@ -0,0 +1,54 @@
+import { Body, Controller, HttpCode, HttpException, Post, Req, Res, UseGuards } from '@nestjs/common';
+import type { Request, Response } from 'express';
+import { NativeAuthService } from './native-auth.service';
+import { NativeExchangeDto, NativeHandoffDto } from './native-auth.dto';
+import { AuthService } from '../auth/auth.service';
+import { CookieAuthGuard } from '../auth/cookie-auth.guard';
+import { CurrentUser } from '../auth/current-user.decorator';
+import { Public } from '../auth/public.decorator';
+import { AuditService } from '../audit/audit.service';
+import { getClientIp } from '../audit/client-ip';
+import { RateLimitService } from '../common/rate-limit.service';
+import type { User } from '../../types';
+
+const EXCHANGE_WINDOW_MS = 15 * 60 * 1000;
+const EXCHANGE_MAX = 20;
+
+/**
+ * /api/auth/native: the sign-in hand-off between the system browser and the
+ * native app. See the contract in @trek/shared for the whole round trip.
+ */
+@Controller('api/auth/native')
+export class NativeAuthController {
+  constructor(
+    private readonly nativeAuth: NativeAuthService,
+    private readonly auth: AuthService,
+    private readonly audit: AuditService,
+    private readonly rl: RateLimitService,
+  ) {}
+
+  /**
+   * Cookie only: an API or MCP bearer token must not be able to mint itself a
+   * full browser session this way.
+   */
+  @Post('handoff')
+  @UseGuards(CookieAuthGuard)
+  @HttpCode(200)
+  handoff(@Body() body: NativeHandoffDto, @CurrentUser() user: User) {
+    return { code: this.nativeAuth.issueCode(user.id, body.challenge) };
+  }
+
+  @Post('exchange')
+  @Public('the one-time code together with its verifier is the credential')
+  @HttpCode(200)
+  exchange(@Body() body: NativeExchangeDto, @Req() req: Request, @Res({ passthrough: true }) res: Response) {
+    if (!this.rl.check('native-exchange', req.ip || 'unknown', EXCHANGE_MAX, EXCHANGE_WINDOW_MS, Date.now())) {
+      throw new HttpException({ error: 'Too many attempts. Please try again later.' }, 429);
+    }
+    const session = this.nativeAuth.redeem(body.code, body.verifier);
+    if (!session) throw new HttpException({ error: 'Invalid or expired code' }, 400);
+    this.auth.setAuthCookie(res, session.token, req, true);
+    this.audit.writeAudit({ userId: session.userId, action: 'user.login', ip: getClientIp(req), details: { method: 'native_app' } });
+    return { ok: true };
+  }
+}
diff --git a/server/src/nest/native-auth/native-auth.dto.ts b/server/src/nest/native-auth/native-auth.dto.ts
new file mode 100644
index 000000000..2ffdfc3ea
--- /dev/null
+++ b/server/src/nest/native-auth/native-auth.dto.ts
@@ -0,0 +1,5 @@
+import { createZodDto } from 'nestjs-zod';
+import { nativeExchangeRequestSchema, nativeHandoffRequestSchema } from '@trek/shared';
+
+export class NativeHandoffDto extends createZodDto(nativeHandoffRequestSchema) {}
+export class NativeExchangeDto extends createZodDto(nativeExchangeRequestSchema) {}
diff --git a/server/src/nest/native-auth/native-auth.module.ts b/server/src/nest/native-auth/native-auth.module.ts
new file mode 100644
index 000000000..a6972e0cb
--- /dev/null
+++ b/server/src/nest/native-auth/native-auth.module.ts
@@ -0,0 +1,13 @@
+import { Module } from '@nestjs/common';
+import { NativeAuthController } from './native-auth.controller';
+import { NativeAuthService } from './native-auth.service';
+import { AuthModule } from '../auth/auth.module';
+import { AuditModule } from '../audit/audit.module';
+import { RateLimitModule } from '../common/rate-limit.module';
+
+@Module({
+  imports: [AuthModule, AuditModule, RateLimitModule],
+  controllers: [NativeAuthController],
+  providers: [NativeAuthService],
+})
+export class NativeAuthModule {}
diff --git a/server/src/nest/native-auth/native-auth.service.ts b/server/src/nest/native-auth/native-auth.service.ts
new file mode 100644
index 000000000..de956f281
--- /dev/null
+++ b/server/src/nest/native-auth/native-auth.service.ts
@@ -0,0 +1,78 @@
+import { Injectable, OnModuleDestroy } from '@nestjs/common';
+import crypto from 'crypto';
+import { DatabaseService } from '../database/database.service';
+import { AuthService } from '../auth/auth.service';
+
+export const NATIVE_HANDOFF_CODE_TTL_MS = 60_000;
+const SWEEP_INTERVAL_MS = 5 * 60_000;
+
+interface PendingHandoff {
+  userId: number;
+  challenge: string;
+  created: number;
+}
+
+/** Constant-time check that sha256(verifier) is the challenge the code was issued for. */
+function verifierMatches(challenge: string, verifier: string): boolean {
+  const expected = Buffer.from(challenge, 'hex');
+  const actual = crypto.createHash('sha256').update(verifier, 'utf8').digest();
+  return expected.length === actual.length && crypto.timingSafeEqual(expected, actual);
+}
+
+/**
+ * Carries a session from the system browser into the native app's WebView.
+ *
+ * Codes live in memory like the OIDC auth codes: they are good for a minute,
+ * a restart simply means signing in again, and nothing about them is worth
+ * a table.
+ */
+@Injectable()
+export class NativeAuthService implements OnModuleDestroy {
+  private readonly pending = new Map<string, PendingHandoff>();
+  private readonly sweeper: NodeJS.Timeout;
+
+  constructor(
+    private readonly db: DatabaseService,
+    private readonly auth: AuthService,
+  ) {
+    this.sweeper = setInterval(() => {
+      const now = Date.now();
+      for (const [code, entry] of this.pending) {
+        if (now - entry.created > NATIVE_HANDOFF_CODE_TTL_MS) this.pending.delete(code);
+      }
+    }, SWEEP_INTERVAL_MS);
+    this.sweeper.unref();
+  }
+
+  onModuleDestroy(): void {
+    clearInterval(this.sweeper);
+  }
+
+  issueCode(userId: number, challenge: string): string {
+    const code = crypto.randomBytes(32).toString('base64url');
+    this.pending.set(code, { userId, challenge, created: Date.now() });
+    return code;
+  }
+
+  /**
+   * Burns the code on every attempt, right or wrong, so a code that leaked
+   * through the URL scheme gets exactly one guess. The session is always the
+   * long one: an app that forgets its login whenever iOS unloads it would be
+   * useless on the road.
+   */
+  redeem(code: string, verifier: string): { token: string; userId: number } | null {
+    const entry = this.pending.get(code);
+    if (!entry) return null;
+    this.pending.delete(code);
+    if (Date.now() - entry.created > NATIVE_HANDOFF_CODE_TTL_MS) return null;
+    if (!verifierMatches(entry.challenge, verifier)) return null;
+
+    const user = this.db.get<{ id: number; password_version: number }>(
+      'SELECT id, password_version FROM users WHERE id = ?',
+      entry.userId,
+    );
+    if (!user) return null;
+    this.db.run('UPDATE users SET last_login = CURRENT_TIMESTAMP, login_count = login_count + 1 WHERE id = ?', user.id);
+    return { token: this.auth.generateToken(user, true), userId: user.id };
+  }
+}
diff --git a/server/src/nest/platform/platform.routes.ts b/server/src/nest/platform/platform.routes.ts
index 1d30bf779..8d4176179 100644
--- a/server/src/nest/platform/platform.routes.ts
+++ b/server/src/nest/platform/platform.routes.ts
@@ -185,6 +185,8 @@ export function applyPlatformSpa(app: express.Application): void {
   });
 }
 
+const HASHED_ASSET = /[\\/]assets[\\/][^\\/]+-[\w-]{8,}\.\w+$/;
+
 /**
  * Production static serving of the built client (JS/CSS/assets). Split out from
  * applyPlatformSpa because the NestJS bootstrap needs the static files served
@@ -200,6 +202,11 @@ export function applyPlatformStatic(app: express.Application): void {
       setHeaders: (res, filePath) => {
         if (filePath.endsWith('index.html')) {
           res.setHeader('Cache-Control', 'no-cache, no-store, must-revalidate');
+        } else if (HASHED_ASSET.test(filePath)) {
+          // Vite puts a content hash in every name under assets/, so a file there
+          // never changes. Without this the iOS app, which has no service worker,
+          // cannot start offline: WebKit would revalidate each script and fail.
+          res.setHeader('Cache-Control', 'public, max-age=31536000, immutable');
         }
       },
     }),
diff --git a/server/tests/e2e/native-auth.e2e.test.ts b/server/tests/e2e/native-auth.e2e.test.ts
new file mode 100644
index 000000000..d6d98c203
--- /dev/null
+++ b/server/tests/e2e/native-auth.e2e.test.ts
@@ -0,0 +1,135 @@
+/**
+ * Native sign-in hand-off e2e: the real CookieAuthGuard, the real cookie
+ * service and the real AuthService against a temp SQLite db. Walks the whole
+ * round trip the apps make: the browser side mints a code for a challenge, the
+ * WebView side redeems it with the verifier and walks away with a session
+ * cookie that /api/auth/me accepts.
+ */
+import { describe, it, expect, beforeAll, afterAll, beforeEach, vi } from 'vitest';
+import request from 'supertest';
+import cookieParser from 'cookie-parser';
+import crypto from 'crypto';
+import type { Server } from 'http';
+import { Test } from '@nestjs/testing';
+import { sessionCookie, signSession } from './harness';
+
+const { db } = vi.hoisted(() => {
+  // eslint-disable-next-line @typescript-eslint/no-require-imports
+  const Database = require('better-sqlite3');
+  const tmp = new Database(':memory:');
+  tmp.exec('PRAGMA journal_mode = WAL');
+  tmp.exec('PRAGMA foreign_keys = ON');
+  return { db: tmp };
+});
+
+vi.mock('../../src/db/database', () => ({
+  db,
+  closeDb: () => {},
+  reinitialize: () => {},
+  getPlaceWithTags: () => null,
+  canAccessTrip: () => undefined,
+  isOwner: () => false,
+}));
+vi.mock('../../src/websocket', () => ({ broadcastToUser: vi.fn(), broadcast: vi.fn() }));
+vi.mock('../../src/nest/audit/audit-log.logger', () => ({ LOG_LEVEL: 'error', logInfo: vi.fn(), logDebug: vi.fn(), logError: vi.fn(), logWarn: vi.fn() }));
+
+import { MailerService } from '../../src/nest/notifications/mailer/mailer.service';
+import { createTables } from '../../src/db/schema';
+import { runMigrations } from '../../src/db/migrations';
+import { createUser } from '../helpers/factories';
+import { resetRateLimits } from '../helpers/test-db';
+import { AuthModule } from '../../src/nest/auth/auth.module';
+import { NativeAuthModule } from '../../src/nest/native-auth/native-auth.module';
+import { DatabaseModule } from '../../src/nest/database/database.module';
+import { TrekExceptionFilter } from '../../src/nest/common/trek-exception.filter';
+import { ZodValidationPipe } from '../../src/nest/common/zod-validation.pipe';
+
+const verifier = crypto.randomBytes(32).toString('base64url');
+const challenge = crypto.createHash('sha256').update(verifier).digest('hex');
+
+describe('Native sign-in hand-off e2e', () => {
+  let server: Server;
+  let app: Awaited<ReturnType<typeof build>>;
+  let userId: number;
+
+  async function build() {
+    const moduleRef = await Test.createTestingModule({ imports: [DatabaseModule, AuthModule, NativeAuthModule] })
+      .overrideProvider(MailerService)
+      .useValue({ sendPasswordResetEmail: vi.fn() })
+      .compile();
+    const nest = moduleRef.createNestApplication();
+    nest.use(cookieParser());
+    nest.useGlobalFilters(new TrekExceptionFilter());
+    nest.useGlobalPipes(new ZodValidationPipe());
+    await nest.init();
+    return nest;
+  }
+
+  const handoff = (cookie: string, body: unknown = { challenge }) =>
+    request(server).post('/api/auth/native/handoff').set('Cookie', cookie).send(body as object);
+
+  beforeAll(async () => {
+    createTables(db as never);
+    runMigrations(db as never);
+    userId = createUser(db as never, { username: 'native-e2e' }).user.id;
+    app = await build();
+    server = app.getHttpServer();
+  });
+
+  beforeEach(() => resetRateLimits(app));
+
+  afterAll(async () => {
+    await app.close();
+  });
+
+  it('carries a browser session into a fresh session cookie for the app', async () => {
+    const minted = await handoff(sessionCookie(userId));
+    expect(minted.status).toBe(200);
+    expect(typeof minted.body.code).toBe('string');
+
+    const redeemed = await request(server).post('/api/auth/native/exchange').send({ code: minted.body.code, verifier });
+    expect(redeemed.status).toBe(200);
+    expect(redeemed.body).toEqual({ ok: true });
+    const cookie = (redeemed.headers['set-cookie'] as unknown as string[]).find((c) => c.startsWith('trek_session='));
+    expect(cookie).toMatch(/HttpOnly/);
+    expect(cookie).toMatch(/Max-Age=\d+/);
+
+    const me = await request(server).get('/api/auth/me').set('Cookie', cookie!.split(';')[0]!);
+    expect(me.status).toBe(200);
+    expect(me.body.user.id).toBe(userId);
+
+    const audited = db.prepare("SELECT details FROM audit_log WHERE action = 'user.login' AND user_id = ? ORDER BY id DESC LIMIT 1").get(userId) as { details: string };
+    expect(JSON.parse(audited.details)).toEqual({ method: 'native_app' });
+  });
+
+  it('refuses to mint a code without a cookie session, even for a valid bearer token', async () => {
+    const res = await request(server).post('/api/auth/native/handoff')
+      .set('Authorization', `Bearer ${signSession(userId)}`)
+      .send({ challenge });
+    expect(res.status).toBe(401);
+    expect(res.body.code).toBe('COOKIE_AUTH_REQUIRED');
+  });
+
+  it('validates the challenge shape', async () => {
+    expect((await handoff(sessionCookie(userId), { challenge: 'not-a-hash' })).status).toBe(400);
+  });
+
+  it('refuses a code presented with the wrong verifier, and the code is gone after', async () => {
+    const { code } = (await handoff(sessionCookie(userId))).body;
+    const wrong = await request(server).post('/api/auth/native/exchange').send({ code, verifier: 'x'.repeat(43) });
+    expect(wrong.status).toBe(400);
+    expect(wrong.body.error).toBe('Invalid or expired code');
+    expect(wrong.headers['set-cookie']).toBeUndefined();
+
+    const retry = await request(server).post('/api/auth/native/exchange').send({ code, verifier });
+    expect(retry.status).toBe(400);
+  });
+
+  it('rate-limits the exchange per ip', async () => {
+    for (let i = 0; i < 20; i++) {
+      await request(server).post('/api/auth/native/exchange').send({ code: `nope-${i}`, verifier });
+    }
+    const blocked = await request(server).post('/api/auth/native/exchange').send({ code: 'nope', verifier });
+    expect(blocked.status).toBe(429);
+  });
+});
diff --git a/server/tests/unit/nest/features.controller.test.ts b/server/tests/unit/nest/features.controller.test.ts
index 14c8c0029..3f4deb9b4 100644
--- a/server/tests/unit/nest/features.controller.test.ts
+++ b/server/tests/unit/nest/features.controller.test.ts
@@ -23,17 +23,17 @@ function make(available: boolean, aiEnabled: boolean) {
 describe('FeaturesController (GET /api/health/features)', () => {
   it('FEAT-001: reports both flags on', () => {
     const { controller } = make(true, true);
-    expect(controller.features()).toEqual({ bookingImport: true, aiParsing: true });
+    expect(controller.features()).toEqual({ bookingImport: true, aiParsing: true, nativeApp: true });
   });
 
   it('FEAT-002: reports both flags off', () => {
     const { controller } = make(false, false);
-    expect(controller.features()).toEqual({ bookingImport: false, aiParsing: false });
+    expect(controller.features()).toEqual({ bookingImport: false, aiParsing: false, nativeApp: true });
   });
 
   it('FEAT-003: the two flags are independent', () => {
-    expect(make(true, false).controller.features()).toEqual({ bookingImport: true, aiParsing: false });
-    expect(make(false, true).controller.features()).toEqual({ bookingImport: false, aiParsing: true });
+    expect(make(true, false).controller.features()).toEqual({ bookingImport: true, aiParsing: false, nativeApp: true });
+    expect(make(false, true).controller.features()).toEqual({ bookingImport: false, aiParsing: true, nativeApp: true });
   });
 
   it('FEAT-004: aiParsing asks the addons service for the LLM parsing addon specifically', () => {
diff --git a/server/tests/unit/nest/native-auth.controller.test.ts b/server/tests/unit/nest/native-auth.controller.test.ts
new file mode 100644
index 000000000..16151c7db
--- /dev/null
+++ b/server/tests/unit/nest/native-auth.controller.test.ts
@@ -0,0 +1,73 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import type { Request, Response } from 'express';
+
+import { NativeAuthController } from '../../../src/nest/native-auth/native-auth.controller';
+import type { NativeAuthService } from '../../../src/nest/native-auth/native-auth.service';
+import type { AuthService } from '../../../src/nest/auth/auth.service';
+import type { AuditService } from '../../../src/nest/audit/audit.service';
+import type { RateLimitService } from '../../../src/nest/common/rate-limit.service';
+import type { User } from '../../../src/types';
+
+const challenge = 'a'.repeat(64);
+const verifier = 'v'.repeat(43);
+
+function build(opts: { redeem?: { token: string; userId: number } | null; allowed?: boolean } = {}) {
+  const nativeAuth = {
+    issueCode: vi.fn().mockReturnValue('code-1'),
+    redeem: vi.fn().mockReturnValue(opts.redeem === undefined ? { token: 'jwt', userId: 7 } : opts.redeem),
+  } as unknown as NativeAuthService;
+  const auth = { setAuthCookie: vi.fn() } as unknown as AuthService;
+  const audit = { writeAudit: vi.fn() } as unknown as AuditService;
+  const rl = { check: vi.fn().mockReturnValue(opts.allowed ?? true) } as unknown as RateLimitService;
+  return { controller: new NativeAuthController(nativeAuth, auth, audit, rl), nativeAuth, auth, audit, rl };
+}
+
+const req = { ip: '10.0.0.1', headers: {} } as unknown as Request;
+const res = {} as Response;
+
+beforeEach(() => vi.clearAllMocks());
+
+describe('NativeAuthController.handoff', () => {
+  it('issues a code for the signed-in user and the given challenge', () => {
+    const { controller, nativeAuth } = build();
+
+    expect(controller.handoff({ challenge }, { id: 7 } as User)).toEqual({ code: 'code-1' });
+    expect(nativeAuth.issueCode).toHaveBeenCalledWith(7, challenge);
+  });
+});
+
+describe('NativeAuthController.exchange', () => {
+  it('sets a remembered session cookie and audits the login', () => {
+    const { controller, auth, audit } = build();
+
+    expect(controller.exchange({ code: 'code-1', verifier }, req, res)).toEqual({ ok: true });
+    expect(auth.setAuthCookie).toHaveBeenCalledWith(res, 'jwt', req, true);
+    expect(audit.writeAudit).toHaveBeenCalledWith(expect.objectContaining({
+      userId: 7, action: 'user.login', details: { method: 'native_app' },
+    }));
+  });
+
+  it('answers 400 with the generic message when the code does not redeem', () => {
+    const { controller, auth } = build({ redeem: null });
+
+    expect(() => controller.exchange({ code: 'x', verifier }, req, res)).toThrow(
+      expect.objectContaining({ status: 400, response: { error: 'Invalid or expired code' } }),
+    );
+    expect(auth.setAuthCookie).not.toHaveBeenCalled();
+  });
+
+  it('answers 429 once the per-ip bucket is exhausted, before touching the code', () => {
+    const { controller, nativeAuth, rl } = build({ allowed: false });
+
+    expect(() => controller.exchange({ code: 'x', verifier }, req, res)).toThrow(expect.objectContaining({ status: 429 }));
+    expect(rl.check).toHaveBeenCalledWith('native-exchange', '10.0.0.1', 20, 15 * 60 * 1000, expect.any(Number));
+    expect(nativeAuth.redeem).not.toHaveBeenCalled();
+  });
+
+  it('buckets requests without an ip under one key', () => {
+    const { controller, rl } = build();
+    controller.exchange({ code: 'x', verifier }, { headers: {} } as unknown as Request, res);
+
+    expect(rl.check).toHaveBeenCalledWith('native-exchange', 'unknown', 20, expect.any(Number), expect.any(Number));
+  });
+});
diff --git a/server/tests/unit/nest/native-auth.service.test.ts b/server/tests/unit/nest/native-auth.service.test.ts
new file mode 100644
index 000000000..fa3bafdff
--- /dev/null
+++ b/server/tests/unit/nest/native-auth.service.test.ts
@@ -0,0 +1,87 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import crypto from 'crypto';
+
+import { NativeAuthService, NATIVE_HANDOFF_CODE_TTL_MS } from '../../../src/nest/native-auth/native-auth.service';
+import type { DatabaseService } from '../../../src/nest/database/database.service';
+import type { AuthService } from '../../../src/nest/auth/auth.service';
+
+const verifier = 'v'.repeat(43);
+const challenge = crypto.createHash('sha256').update(verifier).digest('hex');
+
+function build(user: { id: number; password_version: number } | null = { id: 7, password_version: 2 }) {
+  const db = { get: vi.fn().mockReturnValue(user ?? undefined), run: vi.fn() } as unknown as DatabaseService;
+  const auth = { generateToken: vi.fn().mockReturnValue('jwt') } as unknown as AuthService;
+  return { service: new NativeAuthService(db, auth), db, auth };
+}
+
+describe('NativeAuthService', () => {
+  let services: NativeAuthService[] = [];
+  const make = (...args: Parameters<typeof build>) => {
+    const built = build(...args);
+    services.push(built.service);
+    return built;
+  };
+
+  beforeEach(() => { services = []; });
+  afterEach(() => {
+    services.forEach((s) => s.onModuleDestroy());
+    vi.useRealTimers();
+  });
+
+  it('redeems a code with the matching verifier into a remembered session', () => {
+    const { service, db, auth } = make();
+    const code = service.issueCode(7, challenge);
+
+    expect(service.redeem(code, verifier)).toEqual({ token: 'jwt', userId: 7 });
+    expect(auth.generateToken).toHaveBeenCalledWith({ id: 7, password_version: 2 }, true);
+    expect(db.run).toHaveBeenCalledWith(expect.stringContaining('last_login'), 7);
+  });
+
+  it('refuses a wrong verifier and burns the code with it', () => {
+    const { service } = make();
+    const code = service.issueCode(7, challenge);
+
+    expect(service.redeem(code, 'w'.repeat(43))).toBeNull();
+    expect(service.redeem(code, verifier)).toBeNull();
+  });
+
+  it('is single use', () => {
+    const { service } = make();
+    const code = service.issueCode(7, challenge);
+
+    expect(service.redeem(code, verifier)).not.toBeNull();
+    expect(service.redeem(code, verifier)).toBeNull();
+  });
+
+  it('refuses an unknown code', () => {
+    const { service } = make();
+    expect(service.redeem('nope', verifier)).toBeNull();
+  });
+
+  it('refuses a code older than its ttl', () => {
+    vi.useFakeTimers();
+    const { service } = make();
+    const code = service.issueCode(7, challenge);
+    vi.advanceTimersByTime(NATIVE_HANDOFF_CODE_TTL_MS + 1);
+
+    expect(service.redeem(code, verifier)).toBeNull();
+  });
+
+  it('refuses a code whose user was deleted in the meantime', () => {
+    const { service, auth } = make(null);
+    const code = service.issueCode(7, challenge);
+
+    expect(service.redeem(code, verifier)).toBeNull();
+    expect(auth.generateToken).not.toHaveBeenCalled();
+  });
+
+  it('sweeps expired codes', () => {
+    vi.useFakeTimers();
+    const { service } = make();
+    const code = service.issueCode(7, challenge);
+    vi.advanceTimersByTime(5 * 60_000 + 1);
+    vi.useRealTimers();
+
+    expect(service.redeem(code, verifier)).toBeNull();
+  });
+});
diff --git a/server/tests/unit/nest/platform.controller.test.ts b/server/tests/unit/nest/platform.controller.test.ts
index b48c44b9a..2579300c5 100644
--- a/server/tests/unit/nest/platform.controller.test.ts
+++ b/server/tests/unit/nest/platform.controller.test.ts
@@ -385,6 +385,25 @@ describe('applyPlatformStatic', () => {
     opts.setHeaders(assetRes, '/some/app.js');
     expect(assetRes.headers['Cache-Control']).toBeUndefined();
   });
+
+  it('marks the hashed files under assets/ immutable, and nothing else', async () => {
+    process.env.NODE_ENV = 'production';
+    const expressMod = (await import('express')).default as unknown as { static: ReturnType<typeof vi.fn> };
+    expressMod.static.mockClear();
+    const { app } = fakeApp();
+    applyPlatformStatic(app);
+    const opts = expressMod.static.mock.calls[0][1] as { setHeaders: (res: unknown, p: string) => void };
+    const header = (p: string) => {
+      const res = makeRes();
+      opts.setHeaders(res, p);
+      return res.headers['Cache-Control'];
+    };
+    expect(header('/app/public/assets/index-DbM4_q2x.js')).toBe('public, max-age=31536000, immutable');
+    expect(header('C:\\app\\public\\assets\\Map-a1B2c3D4.css')).toBe('public, max-age=31536000, immutable');
+    expect(header('/app/public/sw.js')).toBeUndefined();
+    expect(header('/app/public/icons/icon-192.png')).toBeUndefined();
+    expect(header('/app/public/assets/plain.js')).toBeUndefined();
+  });
 });
 
 describe('applyPlatformSpa', () => {
diff --git a/server/vitest.config.ts b/server/vitest.config.ts
index e0d507985..86513422b 100644
--- a/server/vitest.config.ts
+++ b/server/vitest.config.ts
@@ -93,6 +93,9 @@ export default defineConfig({
         'src/nest/llm-parse/**/*.ts': { statements: 91, branches: 85, functions: 85, lines: 94 },
         'src/nest/maps/**/*.ts': { statements: 93, branches: 86, functions: 97, lines: 96 },
         'src/nest/memories/**/*.ts': { statements: 92, branches: 83, functions: 97, lines: 94 },
+        // New domain in this change, fully covered by its unit and e2e suites.
+        // Pinned a little under that until a full run regenerates the block.
+        'src/nest/native-auth/**/*.ts': { statements: 95, branches: 90, functions: 95, lines: 95 },
         'src/nest/notifications/**/*.ts': { statements: 83, branches: 72, functions: 85, lines: 87 },
         'src/nest/oauth/**/*.ts': { statements: 96, branches: 95, functions: 97, lines: 97 },
         'src/nest/oidc/**/*.ts': { statements: 88, branches: 83, functions: 91, lines: 92 },
diff --git a/shared/src/index.ts b/shared/src/index.ts
index 7c4399645..65daba4e7 100644
--- a/shared/src/index.ts
+++ b/shared/src/index.ts
@@ -63,6 +63,7 @@ export * from './appearance/appearance.schema';
 export * from './backup/backup.schema';
 export * from './auth/auth.schema';
 export * from './oidc/oidc.schema';
+export * from './native-auth/native-auth.schema';
 export * from './oauth/oauth.schema';
 export * from './admin/admin.schema';
 
diff --git a/shared/src/native-auth/native-auth.schema.spec.ts b/shared/src/native-auth/native-auth.schema.spec.ts
new file mode 100644
index 000000000..f3e9bbd18
--- /dev/null
+++ b/shared/src/native-auth/native-auth.schema.spec.ts
@@ -0,0 +1,27 @@
+import { nativeExchangeRequestSchema, nativeHandoffRequestSchema } from './native-auth.schema';
+
+import { describe, it, expect } from 'vitest';
+
+const challenge = 'a'.repeat(64);
+
+describe('nativeHandoffRequestSchema', () => {
+  it('accepts a lowercase hex sha256', () => {
+    expect(nativeHandoffRequestSchema.safeParse({ challenge }).success).toBe(true);
+  });
+
+  it('rejects anything that is not 64 lowercase hex characters', () => {
+    expect(nativeHandoffRequestSchema.safeParse({ challenge: 'A'.repeat(64) }).success).toBe(false);
+    expect(nativeHandoffRequestSchema.safeParse({ challenge: 'a'.repeat(63) }).success).toBe(false);
+    expect(nativeHandoffRequestSchema.safeParse({ challenge: 'z'.repeat(64) }).success).toBe(false);
+    expect(nativeHandoffRequestSchema.safeParse({}).success).toBe(false);
+  });
+});
+
+describe('nativeExchangeRequestSchema', () => {
+  it('requires a code and a verifier of at least 43 characters', () => {
+    expect(nativeExchangeRequestSchema.safeParse({ code: 'c', verifier: 'v'.repeat(43) }).success).toBe(true);
+    expect(nativeExchangeRequestSchema.safeParse({ code: 'c', verifier: 'v'.repeat(42) }).success).toBe(false);
+    expect(nativeExchangeRequestSchema.safeParse({ code: '', verifier: 'v'.repeat(43) }).success).toBe(false);
+    expect(nativeExchangeRequestSchema.safeParse({ verifier: 'v'.repeat(43) }).success).toBe(false);
+  });
+});
diff --git a/shared/src/native-auth/native-auth.schema.ts b/shared/src/native-auth/native-auth.schema.ts
new file mode 100644
index 000000000..9ce947faf
--- /dev/null
+++ b/shared/src/native-auth/native-auth.schema.ts
@@ -0,0 +1,30 @@
+import { z } from 'zod';
+
+/**
+ * Sign-in hand-off for the native apps, /api/auth/native.
+ *
+ * The app shows the TREK web UI inside its own WebView, but SSO and passkeys
+ * cannot run there, so it signs in through the system browser instead and has
+ * to carry that session back. The app picks a random verifier and sends only
+ * its sha256 (the challenge) into the browser. The browser, once signed in,
+ * trades the challenge for a one-time code, and the WebView redeems the code
+ * together with the verifier. The code travels through a URL scheme any app
+ * could claim, so without the verifier it is worth nothing.
+ */
+const hexSha256 = z.string().regex(/^[0-9a-f]{64}$/);
+
+export const nativeHandoffRequestSchema = z.object({
+  challenge: hexSha256,
+});
+export type NativeHandoffRequest = z.infer<typeof nativeHandoffRequestSchema>;
+
+export const nativeHandoffResponseSchema = z.object({
+  code: z.string(),
+});
+export type NativeHandoffResponse = z.infer<typeof nativeHandoffResponseSchema>;
+
+export const nativeExchangeRequestSchema = z.object({
+  code: z.string().min(1).max(128),
+  verifier: z.string().min(43).max(128),
+});
+export type NativeExchangeRequest = z.infer<typeof nativeExchangeRequestSchema>;