diff --git a/packages/desktop/__tests__/main-externals.test.ts b/packages/desktop/__tests__/main-externals.test.ts
index b0912e8..88729c0 100644
--- a/packages/desktop/__tests__/main-externals.test.ts
+++ b/packages/desktop/__tests__/main-externals.test.ts
@@ -1,4 +1,4 @@
-import { readFileSync } from 'fs';
+import { readdirSync, readFileSync } from 'fs';
 import { join } from 'path';
 
 /**
@@ -16,12 +16,13 @@ const DESKTOP = join(__dirname, '..');
 function mainImports(): string[] {
   // Read the source rather than importing it: this must reflect what Rollup
   // sees, not what a test bundler resolves.
+  // Every main-process source, discovered rather than listed — a new file that
+  // imports a @wavegrid package is exactly the case this guards.
   const files = [
     'src/main.ts',
-    'src/main/brain.ts',
-    'src/main/doctor.ts',
-    'src/main/ipc.ts',
-    'src/main/network.ts'
+    ...readdirSync(join(DESKTOP, 'src/main'))
+      .filter((f) => f.endsWith('.ts'))
+      .map((f) => `src/main/${f}`)
   ];
   const found = new Set<string>();
   for (const file of files) {
diff --git a/packages/desktop/__tests__/operator-session.test.ts b/packages/desktop/__tests__/operator-session.test.ts
new file mode 100644
index 0000000..4169dce
--- /dev/null
+++ b/packages/desktop/__tests__/operator-session.test.ts
@@ -0,0 +1,49 @@
+import { verifyJwt } from '@wavegrid/server';
+import { openStore } from '@wavegrid/settings';
+
+import { embeddedUrl, operatorToken } from '../src/main/operator-session';
+
+const PROJECT = 'desk-auth';
+
+beforeAll(() => {
+  const store = openStore();
+  store.createProject(PROJECT, { preset: 'ring-6' });
+  store.generateSecrets(PROJECT);
+});
+
+describe('desktop operator session', () => {
+  it('mints a token the server accepts, bound to a revocable session', () => {
+    const store = openStore();
+    store.addUser(PROJECT, 'dan', 'hunter2', 'admin');
+
+    const token = operatorToken(PROJECT);
+    expect(token).not.toBeNull();
+
+    const payload = verifyJwt(token!);
+    expect(payload?.sub).toBe('dan');
+    expect(payload?.role).toBe('admin');
+    // Visible in Access → Sessions, so it can be revoked like any other login.
+    const session = store.listSessions(PROJECT).find((s) => s.id === payload?.sid);
+    expect(session?.userAgent).toContain('wavegrid-desktop');
+  });
+
+  it('prefers an admin over an operator account', () => {
+    const store = openStore();
+    store.addUser(PROJECT, 'guest-op', 'hunter2', 'operator');
+    expect(verifyJwt(operatorToken(PROJECT)!)?.sub).toBe('dan');
+  });
+
+  it('falls back to the login screen when the project has no accounts', () => {
+    const store = openStore();
+    store.createProject('no-users', { preset: 'ring-6' });
+    store.generateSecrets('no-users');
+    expect(operatorToken('no-users')).toBeNull();
+    expect(embeddedUrl('http://127.0.0.1:3000', 'no-users')).toBe('http://127.0.0.1:3000');
+  });
+
+  it('hands the token off in the fragment, never the query', () => {
+    const url = embeddedUrl('http://127.0.0.1:3000', PROJECT);
+    expect(url.startsWith('http://127.0.0.1:3000#wg_token=')).toBe(true);
+    expect(url).not.toContain('?');
+  });
+});
diff --git a/packages/desktop/src/main/laser-view.ts b/packages/desktop/src/main/laser-view.ts
index f6656fa..d1a81af 100644
--- a/packages/desktop/src/main/laser-view.ts
+++ b/packages/desktop/src/main/laser-view.ts
@@ -8,6 +8,8 @@
  */
 import { shell, WebContentsView } from 'electron';
 
+import { status } from '@/main/brain';
+import { embeddedUrl } from '@/main/operator-session';
 import { runtime } from '@/main/runtime';
 import type { LaserSyncState } from '@/types/ipc';
 
@@ -27,8 +29,15 @@ export function resetLaserView(): void {
  * this the embedded UI keeps rendering the previous project's layout.
  */
 export function invalidateLaserView(): void {
+  const previous = loadedUrl;
   loadedUrl = null;
-  if (view && !view.webContents.isDestroyed()) void view.webContents.reload();
+  if (!view || view.webContents.isDestroyed() || !previous) return;
+  // Not `reload()`: the UI strips the session token out of the address once it
+  // has consumed it, so reloading would land on the new project's login screen.
+  void view.webContents.loadURL(embeddedUrl(previous, status().project)).catch(() => {
+    // Brain restarting — the next sync loads it.
+  });
+  loadedUrl = previous;
 }
 
 function ensureView(): WebContentsView | null {
@@ -65,7 +74,9 @@ export function syncLaser(state: LaserSyncState): void {
   if (!v) return;
   if (loadedUrl !== url) {
     loadedUrl = url;
-    void v.webContents.loadURL(url).catch(() => {
+    // Carries a session for the active project, so a project switch doesn't
+    // strand the operator on a login screen inside their own app.
+    void v.webContents.loadURL(embeddedUrl(url, status().project)).catch(() => {
       // Brain not up yet / refused — the renderer shows its own empty state.
     });
   }
diff --git a/packages/desktop/src/main/operator-session.ts b/packages/desktop/src/main/operator-session.ts
new file mode 100644
index 0000000..a833b3b
--- /dev/null
+++ b/packages/desktop/src/main/operator-session.ts
@@ -0,0 +1,59 @@
+/**
+ * Signing the embedded artist UI in, so switching projects doesn't ask the
+ * operator for a password every time.
+ *
+ * Sessions are per project by design (a token minted for project A is not
+ * valid once B is active) and that stays true for anything reaching the brain
+ * over the network. This shortcut applies only to the UI embedded in this
+ * desktop app: whoever is at the keyboard already owns the store — they can
+ * read its secrets, add users and mint access keys — so requiring them to
+ * re-type a password into their own machine protects nothing.
+ *
+ * The session is a real store session with a recognisable user agent, so it
+ * appears in Access → Sessions and can be revoked like any other.
+ */
+import { signJwt } from '@wavegrid/server';
+import { openStore } from '@wavegrid/settings';
+
+const DESKTOP_USER_AGENT = 'wavegrid-desktop (this laptop)';
+const TTL_MS = 12 * 60 * 60 * 1000;
+
+/**
+ * A token for the project's admin, or null when the project has no accounts
+ * yet — the embedded UI then shows its normal login screen.
+ */
+export function operatorToken(project: string): string | null {
+  const store = openStore();
+  if (!store.hasProject(project)) return null;
+  const users = store.listUserInfos(project);
+  const account = users.find((u) => u.role === 'admin') ?? users[0];
+  if (!account) return null;
+
+  // The brain sets this when it starts; set it anyway so a token minted before
+  // the first start is signed with the same project's secret.
+  process.env.WG_JWT_SECRET = store.requireSecret(project, 'jwtSecret');
+
+  const session = store.createSession(project, {
+    username: account.username,
+    role: account.role,
+    ip: '127.0.0.1',
+    userAgent: DESKTOP_USER_AGENT,
+    ttlMs: TTL_MS
+  });
+  return signJwt(account.username, {
+    sid: session.id,
+    role: account.role,
+    ttlSec: Math.floor(TTL_MS / 1000)
+  });
+}
+
+/**
+ * The URL the embedded view should load: the brain's own URL, carrying a
+ * one-shot token in the fragment. A fragment (never a query) keeps the token
+ * out of the server's logs, and the UI strips it from the address on arrival.
+ */
+export function embeddedUrl(url: string, project: string | null): string {
+  if (!project) return url;
+  const token = operatorToken(project);
+  return token ? `${url}#wg_token=${encodeURIComponent(token)}` : url;
+}
diff --git a/packages/ui/__tests__/hand-off-token.test.ts b/packages/ui/__tests__/hand-off-token.test.ts
new file mode 100644
index 0000000..784ef44
--- /dev/null
+++ b/packages/ui/__tests__/hand-off-token.test.ts
@@ -0,0 +1,49 @@
+import { takeTokenFromUrl } from '../src/lib/use-auth';
+
+interface FakeWindow {
+  location: { hash: string; pathname: string; search: string };
+  history: { replaceState: (a: null, b: string, url: string) => void };
+}
+
+function fakeWindow(hash: string): FakeWindow {
+  const w: FakeWindow = {
+    location: { hash, pathname: '/', search: '' },
+    history: {
+      replaceState: (_a, _b, url) => {
+        const i = url.indexOf('#');
+        w.location.hash = i === -1 ? '' : url.slice(i);
+      }
+    }
+  };
+  (globalThis as unknown as { window: FakeWindow }).window = w;
+  return w;
+}
+
+afterEach(() => {
+  delete (globalThis as unknown as { window?: FakeWindow }).window;
+});
+
+describe('takeTokenFromUrl', () => {
+  it('reads the handed-off session and erases it from the address', () => {
+    const w = fakeWindow('#wg_token=abc.def.ghi');
+    expect(takeTokenFromUrl()).toBe('abc.def.ghi');
+    expect(w.location.hash).toBe('');
+  });
+
+  it('decodes a percent-encoded token', () => {
+    fakeWindow('#wg_token=a%2Bb');
+    expect(takeTokenFromUrl()).toBe('a+b');
+  });
+
+  it('keeps any other fragment the UI owns', () => {
+    const w = fakeWindow('#tab=patterns&wg_token=abc');
+    expect(takeTokenFromUrl()).toBe('abc');
+    expect(w.location.hash).toBe('#tab=patterns');
+  });
+
+  it('is a no-op without a handoff', () => {
+    const w = fakeWindow('#tab=patterns');
+    expect(takeTokenFromUrl()).toBeNull();
+    expect(w.location.hash).toBe('#tab=patterns');
+  });
+});
diff --git a/packages/ui/src/lib/use-auth.ts b/packages/ui/src/lib/use-auth.ts
index 601d4ff..75ef349 100644
--- a/packages/ui/src/lib/use-auth.ts
+++ b/packages/ui/src/lib/use-auth.ts
@@ -14,6 +14,23 @@ function decodePayload(token: string): { sub: string } | null {
   }
 }
 
+/**
+ * A session handed to us in the address fragment by a trusted embedder (the
+ * desktop app, which owns the store this token was minted from). Consumed once
+ * and erased from the address — the token stays the only credential, so this is
+ * transport, not a privilege: the server validates it exactly as it would a
+ * token from the login form.
+ */
+export function takeTokenFromUrl(): string | null {
+  if (typeof window === 'undefined') return null;
+  const hash = window.location.hash.replace(/^#/, '');
+  const match = /(?:^|&)wg_token=([^&]+)/.exec(hash);
+  if (!match) return null;
+  const rest = hash.replace(/(?:^|&)wg_token=[^&]+/, '').replace(/^&/, '');
+  window.history.replaceState(null, '', window.location.pathname + window.location.search + (rest ? `#${rest}` : ''));
+  return decodeURIComponent(match[1]);
+}
+
 /** Last username signed in on this device — prefilled after a session ends so
  *  getting back in is one field, not two. */
 const LAST_USER_KEY = 'wg_last_user';
@@ -27,6 +44,18 @@ export function useAuth() {
   const [endedSession, setEndedSession] = useState(false);
 
   useEffect(() => {
+    const handed = takeTokenFromUrl();
+    if (handed) {
+      const payload = decodePayload(handed);
+      if (payload) {
+        localStorage.setItem('wg_token', handed);
+        localStorage.setItem(LAST_USER_KEY, payload.sub);
+        setUser(payload.sub);
+        setToken(handed);
+        setChecked(true);
+        return;
+      }
+    }
     const stored = localStorage.getItem('wg_token');
     if (stored) {
       const payload = decodePayload(stored);