diff --git a/.changeset/mosaic-trim-user-button-tests.md b/.changeset/mosaic-trim-user-button-tests.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/mosaic-trim-user-button-tests.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/packages/mosaic/src/features/user-button/__tests__/user-button.controller.test.tsx b/packages/mosaic/src/features/user-button/__tests__/user-button.controller.test.tsx
deleted file mode 100644
index bd33beabdbf..00000000000
--- a/packages/mosaic/src/features/user-button/__tests__/user-button.controller.test.tsx
+++ /dev/null
@@ -1,285 +0,0 @@
-import { act, fireEvent, render, screen, waitFor } from '@testing-library/react';
-import { describe, expect, it, vi } from 'vitest';
-
-import { deferred, tick } from '../../../machines/__tests__/test-utils';
-import type { UserButtonControllerOptions, UserButtonReadyModel } from '../user-button.controller';
-import { useUserButtonController } from '../user-button.controller';
-import type { UserButtonModel } from '../user-button.model';
-
-function ready(overrides: Partial<UserButtonReadyModel> = {}): UserButtonReadyModel {
-  return {
-    status: 'ready',
-    organizationsEnabled: true,
-    renderBranding: true,
-    activeSession: { sessionId: 'sess_1', name: 'Alice Smith', identifier: 'alice@example.com' },
-    activeOrganization: null,
-    hasOrganizations: false,
-    hidePersonal: false,
-    organizationsLoading: false,
-    memberships: [],
-    suggestions: [],
-    invitations: [],
-    additionalSessions: [],
-    ...overrides,
-  };
-}
-
-function Harness({ model, ...options }: { model: UserButtonModel } & UserButtonControllerOptions) {
-  const c = useUserButtonController(model, options);
-  if (c.status !== 'ready') {
-    return <output data-testid='status'>{c.status}</output>;
-  }
-  return (
-    <div>
-      <output data-testid='status'>{c.status}</output>
-      <output data-testid='mode'>{c.mode ?? 'combined'}</output>
-      <output data-testid='open'>{String(c.open)}</output>
-      <output data-testid='pending'>{c.pendingKey ?? ''}</output>
-      <output data-testid='active-org'>{c.activeOrganization?.organizationId ?? ''}</output>
-      <button
-        type='button'
-        onClick={() => c.onOpenChange?.(true)}
-      >
-        open
-      </button>
-      <button
-        type='button'
-        onClick={() => c.onOpenChange?.(false)}
-      >
-        close
-      </button>
-      <button
-        type='button'
-        onClick={() => c.onSelectOrganization?.('org_1')}
-      >
-        select-org
-      </button>
-      <button
-        type='button'
-        onClick={() => c.onSwitchSession?.('sess_2')}
-      >
-        switch
-      </button>
-      <button
-        type='button'
-        onClick={() => c.onManageAccount?.()}
-      >
-        manage-account
-      </button>
-      {c.customMenuItems?.map(item =>
-        item.href === undefined ? (
-          <button
-            key={item.id}
-            type='button'
-            onClick={item.onClick}
-          >
-            {item.label}
-          </button>
-        ) : (
-          <a
-            key={item.id}
-            href={item.href}
-          >
-            {item.label}
-          </a>
-        ),
-      )}
-    </div>
-  );
-}
-
-describe('useUserButtonController', () => {
-  it('passes loading and hidden through until the model is ready', () => {
-    const { rerender } = render(<Harness model={{ status: 'loading' }} />);
-    expect(screen.getByTestId('status')).toHaveTextContent('loading');
-
-    rerender(<Harness model={{ status: 'hidden' }} />);
-    expect(screen.getByTestId('status')).toHaveTextContent('hidden');
-
-    rerender(<Harness model={ready()} />);
-    expect(screen.getByTestId('status')).toHaveTextContent('ready');
-  });
-
-  it('forces user mode when organizations are disabled, whatever mode was asked for', () => {
-    const { rerender } = render(
-      <Harness
-        model={ready({ organizationsEnabled: false })}
-        mode='organization'
-      />,
-    );
-    expect(screen.getByTestId('mode')).toHaveTextContent('user');
-
-    rerender(
-      <Harness
-        model={ready({ organizationsEnabled: true })}
-        mode='organization'
-      />,
-    );
-    expect(screen.getByTestId('mode')).toHaveTextContent('organization');
-  });
-
-  it('runs a model action through the machine and keys the affordance', async () => {
-    const onSelectOrganization = vi.fn(() => Promise.resolve());
-    render(<Harness model={ready({ onSelectOrganization })} />);
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('select-org'));
-
-    expect(onSelectOrganization).toHaveBeenCalledWith('org_1');
-    await waitFor(() => expect(screen.getByTestId('pending')).toHaveTextContent('select-org:org_1'));
-
-    await act(async () => {
-      await tick();
-    });
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-    expect(screen.getByTestId('pending')).toHaveTextContent('');
-  });
-
-  it('closes immediately on a hand-off and leaves the model action to run', () => {
-    const onManageAccount = vi.fn();
-    render(<Harness model={ready({ onManageAccount })} />);
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('manage-account'));
-
-    expect(onManageAccount).toHaveBeenCalledTimes(1);
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-  });
-
-  it('closes the popover before a custom menu action runs', () => {
-    const onClick = vi.fn();
-    render(
-      <Harness
-        model={ready()}
-        customMenuItems={[{ id: 'docs', label: 'Documentation', onClick }]}
-      />,
-    );
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('Documentation'));
-
-    expect(onClick).toHaveBeenCalledTimes(1);
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-  });
-
-  it('starts closed and opens and closes', () => {
-    render(<Harness model={ready()} />);
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-
-    fireEvent.click(screen.getByText('open'));
-    expect(screen.getByTestId('open')).toHaveTextContent('true');
-
-    fireEvent.click(screen.getByText('close'));
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-  });
-
-  it('holds the popup open when an action fails, even one that would have closed it', async () => {
-    const onSelectOrganization = vi.fn(() => Promise.reject(new Error('cannot switch')));
-    render(<Harness model={ready({ onSelectOrganization })} />);
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('select-org'));
-
-    await act(async () => {
-      await tick();
-    });
-    expect(screen.getByTestId('open')).toHaveTextContent('true');
-    expect(screen.getByTestId('pending')).toHaveTextContent('');
-  });
-
-  it('lets the row be clicked again after a failure', async () => {
-    const onSelectOrganization = vi.fn().mockRejectedValueOnce(new Error('boom')).mockResolvedValueOnce(undefined);
-    render(<Harness model={ready({ onSelectOrganization })} />);
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('select-org'));
-    await act(async () => {
-      await tick();
-    });
-
-    fireEvent.click(screen.getByText('select-org'));
-    expect(onSelectOrganization).toHaveBeenCalledTimes(2);
-
-    await act(async () => {
-      await tick();
-    });
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-  });
-
-  it('refuses a second action while one is in flight', async () => {
-    const pending = deferred<unknown>();
-    const onSelectOrganization = vi.fn(() => pending.promise);
-    const onSwitchSession = vi.fn(() => Promise.resolve());
-    render(<Harness model={ready({ onSelectOrganization, onSwitchSession })} />);
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('select-org'));
-    await waitFor(() => expect(screen.getByTestId('pending')).toHaveTextContent('select-org:org_1'));
-
-    fireEvent.click(screen.getByText('switch'));
-    expect(onSwitchSession).not.toHaveBeenCalled();
-
-    await act(async () => {
-      pending.resolve(undefined);
-      await tick();
-    });
-  });
-
-  it('refuses an action while the popup is closed', () => {
-    const onSelectOrganization = vi.fn(() => Promise.resolve());
-    render(<Harness model={ready({ onSelectOrganization })} />);
-
-    fireEvent.click(screen.getByText('select-org'));
-
-    expect(onSelectOrganization).not.toHaveBeenCalled();
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-  });
-
-  it('stays closed when a dismissed action settles', async () => {
-    const pending = deferred<unknown>();
-    const onSwitchSession = vi.fn(() => pending.promise);
-    render(<Harness model={ready({ onSwitchSession })} />);
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('switch'));
-    await waitFor(() => expect(screen.getByTestId('pending')).toHaveTextContent('switch:sess_2'));
-
-    fireEvent.click(screen.getByText('close'));
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-
-    await act(async () => {
-      pending.resolve(undefined);
-      await tick();
-    });
-    expect(screen.getByTestId('open')).toHaveTextContent('false');
-  });
-
-  it('holds the surface on the model the action started from until it settles', async () => {
-    const pending = deferred<unknown>();
-    const onSwitchSession = vi.fn(() => pending.promise);
-    const { rerender } = render(<Harness model={ready({ onSwitchSession })} />);
-
-    fireEvent.click(screen.getByText('open'));
-    fireEvent.click(screen.getByText('switch'));
-
-    rerender(
-      <Harness
-        model={ready({
-          onSwitchSession,
-          activeOrganization: { kind: 'membership', organizationId: 'org_1', name: 'Other' },
-        })}
-      />,
-    );
-
-    expect(screen.getByTestId('active-org')).toHaveTextContent('');
-    expect(screen.getByTestId('open')).toHaveTextContent('true');
-
-    await act(async () => {
-      pending.resolve(undefined);
-      await tick();
-    });
-
-    expect(screen.getByTestId('active-org')).toHaveTextContent('org_1');
-    expect(screen.getByTestId('open')).toHaveTextContent('true');
-  });
-});
diff --git a/packages/mosaic/src/features/user-button/__tests__/user-button.integration.test.tsx b/packages/mosaic/src/features/user-button/__tests__/user-button.integration.test.tsx
index 38e86877395..f810211b350 100644
--- a/packages/mosaic/src/features/user-button/__tests__/user-button.integration.test.tsx
+++ b/packages/mosaic/src/features/user-button/__tests__/user-button.integration.test.tsx
@@ -277,6 +277,19 @@ describe('UserButton (connected)', () => {
     });
   });
 
+  it('renders the fallback while Clerk is still loading', () => {
+    isUserLoaded = false;
+    renderUserButton({ fallback: <output data-testid='fallback' /> });
+    expect(screen.getByTestId('fallback')).toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: /Open account menu/ })).toBeNull();
+  });
+
+  it('drops the fallback once nobody is signed in', () => {
+    user = null;
+    renderUserButton({ fallback: <output data-testid='fallback' /> });
+    expect(host()).toBeEmptyDOMElement();
+  });
+
   it('renders the trigger and keeps the popover closed until clicked', () => {
     renderUserButton();
     expect(trigger()).toBeInTheDocument();
diff --git a/packages/mosaic/src/features/user-button/__tests__/user-button.layout.test.ts b/packages/mosaic/src/features/user-button/__tests__/user-button.layout.test.ts
deleted file mode 100644
index 9dfe95e4a52..00000000000
--- a/packages/mosaic/src/features/user-button/__tests__/user-button.layout.test.ts
+++ /dev/null
@@ -1,105 +0,0 @@
-import { describe, expect, it } from 'vitest';
-
-import { resolveUserButtonLayout } from '../user-button.layout';
-import type { UserButtonData, UserButtonMode, UserButtonModePriority } from '../user-button.types';
-
-const alice = { sessionId: 'sess_1', name: 'Alice Smith', identifier: 'alice@example.com' };
-const bob = { sessionId: 'sess_2', name: 'Bob Jones', identifier: 'bob@example.com' };
-const foundry = { kind: 'membership', organizationId: 'org_1', name: 'Foundry' } as const;
-
-function resolve(
-  mode: UserButtonMode,
-  data: Partial<UserButtonData> = {},
-  modePriority: UserButtonModePriority = 'organization',
-) {
-  return resolveUserButtonLayout(mode, modePriority, {
-    activeSession: alice,
-    activeOrganization: foundry,
-    hasOrganizations: true,
-    memberships: [foundry],
-    suggestions: [],
-    invitations: [],
-    additionalSessions: [bob],
-    ...data,
-  });
-}
-
-describe('resolveUserButtonLayout, where each action lands', () => {
-  it('spreads them across all four slots in combined mode', () => {
-    expect(resolve('combined').actions).toEqual({
-      header: ['inviteMembers', 'manageLead'],
-      organizationsHeading: ['createOrganization', 'manageAccount', 'signOut'],
-      organizationsFooter: ['createOrganization'],
-      footer: ['switchAccount', 'signOutAll'],
-    });
-  });
-
-  it('carries no account actions at all in organization mode', () => {
-    expect(resolve('organization').actions).toEqual({
-      header: ['inviteMembers', 'manageLead'],
-      organizationsHeading: [],
-      organizationsFooter: ['createOrganization'],
-      footer: [],
-    });
-  });
-
-  it('takes the account actions into the header and the foot in user mode', () => {
-    expect(resolve('user').actions).toEqual({
-      header: ['signOut', 'manageLead'],
-      organizationsHeading: [],
-      organizationsFooter: [],
-      footer: ['switchAccount', 'signOutAll'],
-    });
-  });
-});
-
-describe('resolveUserButtonLayout, what the data settles', () => {
-  it('offers no invitation where no organization is active', () => {
-    expect(resolve('combined', { activeOrganization: null }).actions.header).toEqual(['manageLead']);
-  });
-
-  // With no second account the flyout would open onto one row, so the foot offers that row instead.
-  // "All accounts" is that one account too, and the account's own row already signs out of it.
-  it.each<UserButtonMode>(['combined', 'user'])(
-    'leaves the foot "Add account" alone in %s mode where there is one account',
-    mode => {
-      expect(resolve(mode, { additionalSessions: [] }).actions.footer).toEqual(['addAccount']);
-    },
-  );
-});
-
-describe('resolveUserButtonLayout, which sections render', () => {
-  it('heads the organizations with the account even where it belongs to none', () => {
-    const layout = resolve('combined', { hasOrganizations: false, memberships: [], activeOrganization: null });
-
-    expect(layout.showOrganizationsHeading).toBe(true);
-    expect(layout.showOrganizations).toBe(false);
-  });
-
-  it('counts an invitation or a suggestion as something to list', () => {
-    const invitation = {
-      kind: 'invitation',
-      id: 'inv_1',
-      organizationId: 'org_2',
-      organizationName: 'Other Co',
-      status: 'pending',
-    } as const;
-    const data = { hasOrganizations: false, memberships: [], activeOrganization: null };
-
-    expect(resolve('combined', data).showOrganizations).toBe(false);
-    expect(resolve('combined', { ...data, invitations: [invitation] }).showOrganizations).toBe(true);
-  });
-
-  it('carries no organizations in user mode', () => {
-    expect(resolve('user')).toMatchObject({ showOrganizations: false, showOrganizationsHeading: false });
-  });
-});
-
-describe('resolveUserButtonLayout, what the surface leads with', () => {
-  it('takes the priority only where there are two things to choose between', () => {
-    expect(resolve('combined', {}, 'user').leadWith).toBe('user');
-    expect(resolve('combined', {}, 'organization').leadWith).toBe('organization');
-    expect(resolve('organization', {}, 'user').leadWith).toBe('organization');
-    expect(resolve('user', {}, 'organization').leadWith).toBe('user');
-  });
-});
diff --git a/packages/mosaic/src/features/user-button/__tests__/user-button.test.tsx b/packages/mosaic/src/features/user-button/__tests__/user-button.test.tsx
deleted file mode 100644
index f0975997677..00000000000
--- a/packages/mosaic/src/features/user-button/__tests__/user-button.test.tsx
+++ /dev/null
@@ -1,149 +0,0 @@
-import { render, screen } from '@testing-library/react';
-import { beforeEach, describe, expect, it, vi } from 'vitest';
-
-import { UserButton } from '../user-button';
-import type { UserButtonController } from '../user-button.controller';
-
-let controller: UserButtonController;
-
-const { useUserButtonModel, useCustomPages } = vi.hoisted(() => ({
-  useUserButtonModel: vi.fn(() => ({ status: 'loading' })),
-  useCustomPages: vi.fn(),
-}));
-
-vi.mock('../user-button.model', () => ({ useUserButtonModel }));
-
-vi.mock('../user-button.controller', () => ({
-  useUserButtonController: () => controller,
-}));
-
-// The two bridges are told apart by the built-in page list each was given.
-vi.mock('../user-button.pages', () => ({
-  useUserProfilePages: () => ['account'],
-  useOrganizationProfilePages: () => ['general'],
-  useCustomPages,
-}));
-
-// The wrapper's own job is which of the three controller states renders what, so the surface is
-// stubbed out and the view's own tests cover it.
-vi.mock('../user-button.view', () => ({
-  UserButtonView: () => <output data-testid='view' />,
-}));
-
-function ready(): UserButtonController {
-  return {
-    status: 'ready',
-    renderBranding: true,
-    activeSession: { sessionId: 'sess_1', name: 'Alice Smith', identifier: 'alice@example.com' },
-    activeOrganization: null,
-    hasOrganizations: false,
-    hidePersonal: false,
-    organizationsLoading: false,
-    memberships: [],
-    suggestions: [],
-    invitations: [],
-    additionalSessions: [],
-  };
-}
-
-describe('UserButton', () => {
-  beforeEach(() => {
-    controller = { status: 'loading' };
-    useUserButtonModel.mockClear();
-    useCustomPages.mockImplementation(({ builtInPages }: { builtInPages: readonly string[] }) => ({
-      customPages: [{ label: `${builtInPages[0]}-page` }],
-      portals: [
-        <output
-          key={builtInPages[0]}
-          data-testid={`${builtInPages[0]}-portal`}
-        />,
-      ],
-    }));
-  });
-
-  it('stands the fallback in while Clerk is still answering', () => {
-    render(<UserButton fallback={<output data-testid='fallback' />} />);
-    expect(screen.getByTestId('fallback')).toBeInTheDocument();
-    expect(screen.queryByTestId('view')).not.toBeInTheDocument();
-  });
-
-  // Signing out is an answer, not a wait. Holding the placeholder there would promise a button to
-  // someone who is never going to get one.
-  it('drops the fallback once nobody is signed in', () => {
-    controller = { status: 'hidden' };
-    render(<UserButton fallback={<output data-testid='fallback' />} />);
-    expect(screen.queryByTestId('fallback')).not.toBeInTheDocument();
-    expect(screen.queryByTestId('view')).not.toBeInTheDocument();
-  });
-
-  it('renders the surface once the session is ready', () => {
-    controller = ready();
-    render(<UserButton fallback={<output data-testid='fallback' />} />);
-    expect(screen.getByTestId('view')).toBeInTheDocument();
-    expect(screen.queryByTestId('fallback')).not.toBeInTheDocument();
-  });
-
-  it('renders no fallback while loading when none is given', () => {
-    render(<UserButton />);
-    expect(screen.queryByTestId('fallback')).not.toBeInTheDocument();
-    expect(screen.queryByTestId('view')).not.toBeInTheDocument();
-  });
-
-  it('keeps the custom page portals of both profiles mounted in every state', () => {
-    const { rerender } = render(<UserButton />);
-    expect(screen.getByTestId('account-portal')).toBeInTheDocument();
-    expect(screen.getByTestId('general-portal')).toBeInTheDocument();
-
-    controller = { status: 'hidden' };
-    rerender(<UserButton />);
-    expect(screen.getByTestId('account-portal')).toBeInTheDocument();
-    expect(screen.getByTestId('general-portal')).toBeInTheDocument();
-
-    controller = ready();
-    rerender(<UserButton />);
-    expect(screen.getByTestId('account-portal')).toBeInTheDocument();
-    expect(screen.getByTestId('general-portal')).toBeInTheDocument();
-  });
-
-  it('hands the model each profile modal its props, and keeps the routing options apart', () => {
-    const appearance = { variables: { colorPrimary: 'red' } };
-    const additionalOAuthScopes = { google: ['https://www.googleapis.com/auth/calendar'] };
-    const apiKeysProps = { showDescription: true };
-    render(
-      <UserButton
-        afterLeaveOrganizationUrl='/left'
-        userProfileProps={{ additionalOAuthScopes, apiKeysProps, appearance }}
-        organizationProfileProps={{ appearance }}
-      />,
-    );
-
-    expect(useUserButtonModel).toHaveBeenCalledWith(
-      { afterLeaveOrganizationUrl: '/left' },
-      {
-        userProfile: { customPages: [{ label: 'account-page' }], additionalOAuthScopes, apiKeysProps, appearance },
-        organizationProfile: { customPages: [{ label: 'general-page' }], appearance },
-      },
-    );
-  });
-
-  it('bridges each profile its own custom pages, ordered against its own built-in pages', () => {
-    const page = { label: 'Usage', path: 'usage', content: <p>Usage</p> };
-    render(
-      <UserButton
-        userProfileProps={{ customPages: [page], pageOrder: ['usage', 'account'] }}
-        organizationProfileProps={{ customPages: [page], pageOrder: ['members', 'usage'] }}
-      />,
-    );
-
-    expect(useCustomPages).toHaveBeenCalledWith({
-      items: [page],
-      order: ['usage', 'account'],
-      builtInPages: ['account'],
-    });
-    expect(useCustomPages).toHaveBeenCalledWith({
-      items: [page],
-      order: ['members', 'usage'],
-      builtInPages: ['general'],
-    });
-  });
-});