Removed/unauthorized Telegram users could inject prompt content before the
per-user auth gate fired. The adapter ran `_should_process_message`,
`_build_message_event`, and text/photo batching — and dispatched to the
runner — before `_is_user_authorized()` (gateway/authz_mixin.py) rejected
the sender. Unmentioned group chatter from a removed user was also
persisted into the session transcript via `_observe_unmentioned_group_message`,
leaking into the agent's observed context independent of dispatch.
Add `_is_user_authorized_from_message()` as an intake prefilter that runs
in `_handle_text_message`, `_handle_command`, `_handle_location_message`,
and `_handle_media_message` BEFORE batching, event construction, and the
unmentioned-group observe branch. It reuses the runner's
`_is_user_authorized()` with a correctly-shaped SessionSource (group vs
forum vs dm, real chat_id for TELEGRAM_GROUP_ALLOWED_* allowlists),
falls back to env allowlists, and only rejects when an allowlist actually
exists — unknown DMs with no allowlist still reach the pairing flow.
Channel posts authorize via `sender_chat` identity when `from_user` is
absent.
Co-authored-by: liuhao1024 <sunsky.lau@gmail.com>
Co-authored-by: Carlos Manuel Cejas <carlosmcejas@gmail.com>
