app: a sign-in that comes back from the PDS but can't be completed now says so instead of looping to the session-expired toast — initSession checked isSessionDead before isCallback, so a refused code exchange (invalid_grant) was marked as an expiry, and any other callback error fell through to App's signed-out fallback, which raised the same toast; either way the user landed back on "Your session expired — Sign in" with no reason (reported on Chrome/Android, where it loops while Firefox signs in fine). Callback failures now log auth.callbackFailed and throw SignInFailedError, App hands its message to authNotice.signInError, and the toast reads "Sign-in didn't finish — try again." with the library's error underneath. Still silent: a page killed between the library stripping the callback params and finishing the exchange. Verified in the preview with a bogus ?state=&code= callback: the toast shows "Unknown authorization session"; pnpm check 0 errors 0 warnings