When reply_to_message config is enabled, the bot's first reply now
uses reply_in_thread=True to create a visual topic/thread in the
Feishu client. Subsequent chunks fall back to regular create.
The reply_to_message default remains False for backward compatibility.
Failed replies still fall back to regular send — messages are never
silently dropped.
Thread replies (messages with root_id != message_id) in group chats
now get their own session key: feishu:{chat_id}:{root_id}. This
means each Feishu thread has an independent conversation context.
Top-level group messages and all private chat messages keep the
default session key (no override), consistent with Telegram and
Slack channel behavior.
Co-authored-by: shenchengtsi <228445050+shenchengtsi@users.noreply.github.com>
