Someone invites you to their workspace. You get an email, you sign up, you verify. Now you need to say yes — and the only "yes" button in the whole repo is on a page of the account website (services/web, account-page.vue). If you are sitting in the browser app, signed in, looking at your workspace list, there is no way to accept. You have to know a separate website exists and go there.
This is the one finding that survived §78's superseded fold-the-account-site plan. It has nothing to do with which front-end owns sign-up; it is true whether or not services/web exists. Notepad: notepad/78-invitations-in-app.md.
Scope, confirmed: browser only. apps/desktop is pinned to one workspace (tauri.ts:54 → tenantSwitching: { kind: 'unsupported' }), so joining a second one is meaningless there. The block renders only where switching is supported. On desktop this plan changes nothing, and that is stated rather than papered over.