#42463 made Logout revoke the dashboard session key on the server. Both
logout specs ran on the shared ADMIN_STORAGE_PATH session that globalSetup
mints once, so clicking Logout revoked the key every later admin spec reuses.
The CircleCI run is serial, and from the auth/ folder on, every admin-session
spec failed with "Invalid proxy server token passed" (80 failures, up from 7)
while the internal-user, internal-viewer and team-admin specs kept passing.
Each logout spec now starts from an empty storage state and logs in through
the login page, so the session it revokes is its own. The login steps live in
a shared logInThroughLoginPage helper next to the other onboarding helpers.
