_is_callback_user_authorized resolved the gateway's auth chain through
_message_handler.__self__. For a secondary multiplexed adapter the
message handler is a per-profile closure with no __self__, so the
introspection silently fell through to the env-only fallback -- which
knows nothing about config allowlists or the pairing store, denying
every button caller on that profile (fail-closed, but wrong).
Prefer the auth callback GatewayRunner already injects at connection
time via set_authorization_check (registered for primary and multiplexed
adapters alike, delegating to the full _is_user_authorized chain), and
keep the introspection plus env fallback for adapters wired without it.
Same resolution pattern the admin-tier gate uses.
4346721117