Friend chat: friend's Bot replies have no avatar; thinking row flashes, then a second one appears #443

Reported 2026-10-19 18:41 (Asia/Shanghai) on a test build of main + #434 + #440, in a Bot Social friend chat with a friend's Bot (测试 (Danyang)):

1. The friend's Bot's reply bubbles have no avatar; the slot beside the bubble is empty. The sidebar row and the header show the Bot's orange mark fine.
2. While the friend's Bot is replying, the thinking row flashes in briefly and goes away.
3. Later a second thinking line ("… is thinking…") shows up below the last message, with no avatar, and can linger after the reply landed.

Cause:

• A friend's 1:1 chat answers in two short turns: my message leaves in one turn (the remote route forwards it and the turn ends right away), and the reply comes back later as a separate echo turn. The activity row only lives while a turn runs, so it shows for the send turn, disappears, and then the social plugin's own PeerThinking dock line (text only, presence polled every 2 s) takes over. That gives the flash, the second row, and the missing avatar.
• AssistantCell draws a friend chat's replies as plain Bubbles with no lead. Remote Bots get their mark only in group chats (RemoteMessage).

Expected: the friend's Bot's replies carry its mark, the one the sidebar shows, and one steady thinking row, also with its mark, stays up from send until the reply lands. No flash, no duplicate.