Session-scoped /model and /reasoning overrides were silently lost on
Telegram DM/forum topics and after compression session splits (#30479).
Root cause: _handle_message_with_agent rewrites source.thread_id via
_recover_telegram_topic_thread_id (lobby/stripped reply -> the user's
bound topic) before deriving the session key. The /model and /reasoning
handlers derived their override key from the raw inbound event.source,
skipping that recovery, so the override was stored under one key and the
next message turn read a different key.
Fix: add _normalize_source_for_session_key (applies the same recovery a
message turn does) and use it in both handlers before deriving the key.
session_id rotation on compression was never the cause — overrides are
keyed by the durable session_key; the split path preserves it.
Author: teknium1 <127238744+teknium1@users.noreply.github.com>
