diff --git a/docs/systems/auth.md b/docs/systems/auth.md
index af53070c..0015f7f7 100644
--- a/docs/systems/auth.md
+++ b/docs/systems/auth.md
@@ -561,6 +561,8 @@ Called by `useAuth()` hook when token exists but user object is null:
   3. `initSession(token, finalUser)` -- activates Zustand state, triggers redirect
   4. Navigate to redirect param or `/channels/@me`
 
+  **Auth-token source of truth.** During the step-2 avatar upload, the JWT lives in `localStorage` only -- `authStore.token` (Zustand) is still null because step 3 hasn't fired. Both the home `api` client (`api/client.ts`) and the home-origin branch of `setTokenForOriginResolver` in `instanceStore.ts` therefore read the home JWT from `localStorage.getItem('backspace_token')`, never from `authStore.token`. This keeps `transferStore.startUpload` (and any other path that resolves a home-origin bearer) authenticated during the registration window. The two stores are written together everywhere else (`initSession`/`logout`), so the divergence only matters between steps 1 and 3 here.
+
 ---
 
 ## 8. Federation-Aware Identity Utilities
diff --git a/packages/web/src/stores/instanceStore.tokenResolver.test.ts b/packages/web/src/stores/instanceStore.tokenResolver.test.ts
new file mode 100644
index 00000000..a56daafb
--- /dev/null
+++ b/packages/web/src/stores/instanceStore.tokenResolver.test.ts
@@ -0,0 +1,69 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+
+// Same shims as instanceStore.failover.test.ts so importing instanceStore
+// doesn't pull in real WS / audio / federation machinery.
+vi.mock('../utils/dmOriginFailover', () => ({
+  failoverDmOriginsFromDisconnected: vi.fn(),
+}));
+vi.mock('../hooks/useWebSocket', () => ({
+  connectInstance: vi.fn(),
+  disconnectInstance: vi.fn(),
+  disconnectAllRemote: vi.fn(),
+}));
+vi.mock('../utils/federationOps', () => ({ clearPasswordSyncTimers: vi.fn() }));
+vi.mock('../audio/AudioManager', () => ({
+  AudioManager: { getInstance: vi.fn().mockReturnValue({ setOutputDevice: vi.fn(), setVolume: vi.fn() }) },
+}));
+// authStore.token is forced to null for every test in this file — that's the
+// invariant we're verifying the resolver tolerates (registration window).
+vi.mock('./authStore', () => ({
+  useAuthStore: Object.assign(
+    (selector: (s: unknown) => unknown) => selector({ user: null, token: null }),
+    { getState: () => ({ user: null, token: null }), setState: vi.fn(), subscribe: vi.fn() }
+  ),
+}));
+
+// Importing instanceStore registers the production resolver.
+import { useInstanceStore } from './instanceStore';
+import { getTokenForOrigin } from '../utils/crossStoreResolvers';
+
+beforeEach(() => {
+  localStorage.clear();
+  useInstanceStore.setState({ instances: [], registry: new Map(), registryUpdatedAt: 0 });
+});
+
+describe('home-origin token resolver', () => {
+  // Regression: during the RegisterPage step-2 avatar upload window, the JWT
+  // is in localStorage but authStore.token is still null (initSession is
+  // intentionally deferred so AuthRedirect doesn't yank the user off /register
+  // mid-upload). The home `api` client reads localStorage directly, so the
+  // token resolver must too — otherwise transferStore.startUpload throws
+  // "not authenticated" and the avatar upload silently fails.
+  it('returns localStorage token for empty origin when authStore.token is null', () => {
+    localStorage.setItem('backspace_token', 'register-window-jwt');
+    expect(getTokenForOrigin('')).toBe('register-window-jwt');
+  });
+
+  it('returns null for empty origin when localStorage has no token', () => {
+    expect(getTokenForOrigin('')).toBeNull();
+  });
+
+  it('returns the per-instance token for a known remote origin', () => {
+    useInstanceStore.setState({
+      instances: [{
+        origin: 'https://remote.example.com',
+        label: 'remote',
+        token: 'remote-jwt',
+        username: 'u',
+        status: 'connected',
+        user: { id: 'u', username: 'u' } as never,
+        api: {} as never,
+      }],
+    });
+    expect(getTokenForOrigin('https://remote.example.com')).toBe('remote-jwt');
+  });
+
+  it('returns null for an unknown remote origin', () => {
+    expect(getTokenForOrigin('https://unknown.example.com')).toBeNull();
+  });
+});
diff --git a/packages/web/src/stores/instanceStore.ts b/packages/web/src/stores/instanceStore.ts
index 5ecd3a19..f9523872 100644
--- a/packages/web/src/stores/instanceStore.ts
+++ b/packages/web/src/stores/instanceStore.ts
@@ -1160,11 +1160,19 @@ setUserIdForOriginResolver((origin: string): string | undefined => {
 // ─── Token resolution (federation) ────────────────────────────────────────────
 // Maps an origin to the JWT for that instance. Used by transferStore for tus
 // uploads and any other path that constructs raw HTTP requests to a federated
-// instance and needs to pass an Authorization header. Empty origin falls back
-// to the home-instance token from authStore.
+// instance and needs to pass an Authorization header.
+//
+// Empty origin reads from localStorage, mirroring the home `api` client
+// (api/client.ts). authStore.token is the React-state mirror of the same value
+// and is written together with localStorage by initSession/logout — but the
+// register page intentionally writes localStorage *before* initSession (so
+// AuthRedirect doesn't yank the user off /register while the avatar is still
+// uploading). Reading authStore.token here would return null in that window
+// and the upload would silently fail. Aligning with the api client closes the
+// gap and gives one source of truth for the home JWT.
 
 setTokenForOriginResolver((origin: string): string | null => {
-  if (!origin) return useAuthStore.getState().token;
+  if (!origin) return localStorage.getItem('backspace_token');
   const instance = useInstanceStore.getState().instances.find(i => i.origin === origin);
   return instance?.token ?? null;
 });