[BUG] Terminal viewport drops the assistant message being read when a new turn arrives (background session); message still visible via ctrl+o

Environment

• Claude Code 2.1.219, Linux (native, not WSL)
• Background (daemon-managed) session, viewed live in a terminal (VS Code integrated terminal)
• Observed trigger: an in-session scheduled prompt (cron reminder) firing, but the mechanism looks like "any newly arriving turn"

What happens

While reading the most recent assistant message in the normal terminal view, a new turn arrives (in our case, a cron-scheduled prompt firing into the session). The assistant message being read disappears from the main viewport entirely. It is not truncated or scrolled out of view, it is simply gone from the rendered conversation.

The content itself is intact: the session .jsonl still contains the message, and the ctrl+o transcript view still shows it. So this is a main-viewport rendering drop, not data loss.

Why it matters

From the reader's perspective this is silent message loss. Nothing indicates that content vanished, so unless a conversation is visibly in progress the user has no way to know an assistant message ever existed. Keeping the ctrl+o view open permanently is not a practical workaround.

Reproduction (observed repeatedly on 2.1.219)

1. Run a background session and let the assistant produce a long final message.
2. While reading it in the main view, have a new user-role turn arrive; a scheduled cron prompt firing into the session does this reliably.
3. The assistant message disappears from the main viewport. ctrl+o still shows it, and the .jsonl carries it.

Most recent occurrence: the arriving turn was an hourly scheduled prompt, and the wiped message was the immediately preceding long assistant reply the user was in the middle of reading. This has happened on multiple days, always in the background-session terminal view.

Happy to provide session timestamps or more environment detail if useful.