POST /api/me/switch validated wallet membership, access and suspension but not
the target account's session epoch. Switching to an account revoked elsewhere (a
password reset/change or "log out everywhere" bumped its epoch) made it the
session default, so the next request's current_user hit the epoch mismatch on
the default identity and cleared the WHOLE wallet session — logging out every
account in the browser. Mirror the suspend guard: drop the stale account from
the switch list and return 403 instead of switching.