diff --git a/.changeset/mosaic-switcher-mutation-tests.md b/.changeset/mosaic-switcher-mutation-tests.md
new file mode 100644
index 00000000000..a845151cc84
--- /dev/null
+++ b/.changeset/mosaic-switcher-mutation-tests.md
@@ -0,0 +1,2 @@
+---
+---
diff --git a/packages/mosaic/src/features/organization-switcher/__tests__/organization-switcher.feature.test.tsx b/packages/mosaic/src/features/organization-switcher/__tests__/organization-switcher.feature.test.tsx
index 8a2cc51c25c..278fd3d049e 100644
--- a/packages/mosaic/src/features/organization-switcher/__tests__/organization-switcher.feature.test.tsx
+++ b/packages/mosaic/src/features/organization-switcher/__tests__/organization-switcher.feature.test.tsx
@@ -193,6 +193,56 @@ describe('OrganizationSwitcher', () => {
     expect(within(trigger()).getByText('Other')).toBeInTheDocument();
   });
 
+  describe('landing after an action', () => {
+    it('lands on afterSelectPersonalUrl, filled from the account, after switching to the personal account', async () => {
+      const { navigate } = await renderSwitcher({ afterSelectPersonalUrl: '/users/:id' }, noOffers());
+      const user = await openWithList();
+
+      await user.click(screen.getByRole('button', { name: 'Personal account' }));
+
+      await waitFor(() => expect(navigate).toHaveBeenCalledWith('/users/user_1'));
+    });
+
+    it('lands where an afterSelectOrganizationUrl function points for the selected organization', async () => {
+      const { navigate } = await renderSwitcher(
+        { afterSelectOrganizationUrl: organization => `/orgs/${organization.name}` },
+        noOffers(),
+      );
+      const user = await openWithList();
+
+      await user.click(screen.getByRole('button', { name: 'Other' }));
+
+      await waitFor(() => expect(navigate).toHaveBeenCalledWith('/orgs/Other'));
+    });
+
+    it('tells the organization profile where to land after leaving', async () => {
+      const { clerk } = await renderSwitcher({ afterLeaveOrganizationUrl: '/left' }, noOffers());
+      const openOrganizationProfile = vi.spyOn(clerk, 'openOrganizationProfile').mockImplementation(() => {});
+      const user = await openWithList();
+
+      await user.click(screen.getByRole('button', { name: 'Settings' }));
+
+      expect(openOrganizationProfile).toHaveBeenCalledWith(
+        expect.objectContaining({ afterLeaveOrganizationUrl: '/left' }),
+      );
+    });
+
+    it('tells create-organization where to land and whether to skip inviting members', async () => {
+      const { clerk } = await renderSwitcher(
+        { afterCreateOrganizationUrl: '/created', skipInvitationScreen: true },
+        noOffers(),
+      );
+      const openCreateOrganization = vi.spyOn(clerk, 'openCreateOrganization').mockImplementation(() => {});
+      const user = await openWithList();
+
+      await user.click(screen.getByRole('button', { name: 'Add organization' }));
+
+      expect(openCreateOrganization).toHaveBeenCalledWith(
+        expect.objectContaining({ afterCreateOrganizationUrl: '/created', skipInvitationScreen: true }),
+      );
+    });
+  });
+
   describe('an accepted invitation', () => {
     const fullFirstPage = Array.from({ length: 10 }, (_, i) =>
       fapiMembership(fapiOrganization({ id: `org_page_${i}`, name: `Page ${i}` })),
diff --git a/packages/mosaic/src/features/user-button/__tests__/user-button.feature.test.tsx b/packages/mosaic/src/features/user-button/__tests__/user-button.feature.test.tsx
index 27b2f9dc87a..4ebb5a240dd 100644
--- a/packages/mosaic/src/features/user-button/__tests__/user-button.feature.test.tsx
+++ b/packages/mosaic/src/features/user-button/__tests__/user-button.feature.test.tsx
@@ -174,8 +174,8 @@ describe('UserButton', () => {
       expect(trigger()).toBeInTheDocument();
     });
 
-    it('renders nothing when nobody is signed in', async () => {
-      await renderUserButton({ mode }, signedIn({ client: fapiClient() }));
+    it('renders nothing, not even its fallback, when nobody is signed in', async () => {
+      await renderUserButton({ mode, fallback: <output>Loading</output> }, signedIn({ client: fapiClient() }));
 
       expect(host()).toBeEmptyDOMElement();
     });
@@ -290,6 +290,19 @@ describe('UserButton', () => {
       expect(popup()).toBeInTheDocument();
     });
 
+    it('lands a switched account where the instance sends it', async () => {
+      const { navigate } = await renderUserButton(
+        {},
+        signedIn({ environment: fapiEnvironment({ display_config: { after_switch_session_url: '/switched' } }) }),
+      );
+      const user = await open();
+
+      const menu = await openAccounts(user);
+      await user.click(within(menu).getByRole('menuitem', { name: 'bob@example.com' }));
+
+      await waitFor(() => expect(navigate).toHaveBeenCalledWith(expect.stringMatching(/\/switched$/)));
+    });
+
     it('signs out of the active account alone while another stays signed in', async () => {
       const { fapi, navigate } = await renderUserButton();
       const user = await open();
@@ -399,6 +412,39 @@ describe('UserButton', () => {
       expect(popup()).toBeInTheDocument();
     });
 
+    it('reports a failed accept, and drops an invitation that is no longer pending', async () => {
+      const log = vi.spyOn(console, 'error').mockImplementation(() => {});
+      const { fapi } = await renderUserButton({}, noOffers({ invitations: [fapiInvitation('inv_1', gamma)] }));
+      const user = await openWithList();
+      const accept = holdRequests('post', '/v1/me/organization_invitations/:id/accept');
+
+      await user.click(screen.getByRole('button', { name: 'Accept' }));
+      fapi.invitations = [fapiInvitation('inv_1', gamma, { status: 'revoked' })];
+      accept.fail('organization_invitation_not_pending');
+
+      await waitFor(() => expect(screen.queryByRole('button', { name: 'Accept' })).toBeNull());
+      expect(reading('Gamma')).toEqual([]);
+      expect(log).toHaveBeenCalledWith(
+        '[Clerk] User button action failed',
+        expect.objectContaining({ errors: [expect.objectContaining({ code: 'organization_invitation_not_pending' })] }),
+      );
+      expect(popup()).toBeInTheDocument();
+    });
+
+    it('shows a suggestion as requested when a failed join finds it already accepted', async () => {
+      vi.spyOn(console, 'error').mockImplementation(() => {});
+      const { fapi } = await renderUserButton({}, noOffers({ suggestions: [fapiSuggestion('sug_1', beta)] }));
+      const user = await openWithList();
+      const join = holdRequests('post', '/v1/me/organization_suggestions/:id/accept');
+
+      await user.click(screen.getByRole('button', { name: 'Join' }));
+      fapi.suggestions = [fapiSuggestion('sug_1', beta, { status: 'accepted' })];
+      join.fail('organization_suggestion_already_accepted');
+
+      await waitFor(() => expect(reading('Beta', 'Requested')).toEqual(['Beta', 'Requested']));
+      expect(screen.queryByRole('button', { name: 'Join' })).toBeNull();
+    });
+
     it('spins inside the join button while the suggestion is joined', async () => {
       await renderUserButton();
       const user = await open();
@@ -577,6 +623,21 @@ describe('UserButton', () => {
       await waitFor(() => expect(popup()).toBeNull());
     });
 
+    it('offers no invite to a member who cannot manage memberships', async () => {
+      const plain = [fapiMembership(acme), fapiMembership(other)];
+      await renderUserButton(
+        {},
+        signedIn({
+          client: fapiClient([fapiSession({ ...aliceSession, user: { ...alice, organization_memberships: plain } })]),
+          memberships: plain,
+        }),
+      );
+      await open();
+
+      expect(screen.getByRole('button', { name: 'Settings' })).toBeInTheDocument();
+      expect(screen.queryByRole('button', { name: 'Invite members' })).toBeNull();
+    });
+
     it('opens the CreateOrganization modal and closes', async () => {
       const { clerk, navigate } = await renderUserButton();
       const openCreateOrganization = vi.spyOn(clerk, 'openCreateOrganization').mockImplementation(() => {});
@@ -813,6 +874,19 @@ describe('UserButton', () => {
     expect(await screen.findByRole('button', { name: 'Org 15' })).toBeInTheDocument();
   });
 
+  it('loads the next page of invitations when the end of the list scrolls into view', async () => {
+    const many = Array.from({ length: 15 }, (_, i) =>
+      fapiInvitation(`inv_p${i + 1}`, fapiOrganization({ id: `org_i${i + 1}`, name: `Invited ${i + 1}` })),
+    );
+    await renderUserButton({}, noOffers({ invitations: many }));
+    await open();
+
+    const last = await screen.findByText('Invited 10');
+    last.scrollIntoView();
+
+    expect(await screen.findByText('Invited 15')).toBeInTheDocument();
+  });
+
   it('lists the active organization where its page puts it, and lists it once', async () => {
     const many = Array.from({ length: 15 }, (_, i) => fapiOrganization({ id: `org_p${i + 1}`, name: `Org ${i + 1}` }));
     await renderUserButton({}, signedIn({ memberships: [...many.map(o => fapiMembership(o)), fapiMembership(acme)] }));
@@ -1077,25 +1151,6 @@ describe('UserButton', () => {
       expect(reading('Gamma', 'Personal account')).toEqual(['Personal account', 'Gamma']);
     });
 
-    it('drops revoked and expired invitations, which have nothing to accept', async () => {
-      await renderUserButton(
-        {},
-        noOffers({
-          invitations: [
-            fapiInvitation('inv_1', gamma, { status: 'revoked' }),
-            fapiInvitation('inv_2', beta, { status: 'expired' }),
-          ],
-        }),
-      );
-      await openWithList();
-
-      expect(reading('Gamma', 'Beta', 'Personal account', 'Acme', 'Other')).toEqual([
-        'Personal account',
-        'Acme',
-        'Other',
-      ]);
-    });
-
     it('reports an accepted suggestion instead of offering to join it again', async () => {
       await renderUserButton({}, noOffers({ suggestions: [fapiSuggestion('sug_1', beta, { status: 'accepted' })] }));
       await openWithList();