[BUG] Cowork: individual user messages missing from chat log (not total truncation) - data intact in backend transcript

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

In Cowork mode (Claude Desktop), individual user turns within a session sometimes fail to render in the chat log, even though surrounding messages display fine. This is related to but different from #42890, which describes ALL history being truncated down to only the last user message. In my case only specific turns are missing, not the whole history.

Steps to reproduce: Have an extended Cowork session with several turns, including at least one user message containing a pasted link. Continue the conversation for several more turns. Scroll back through the session's chat log in the UI. A specific earlier user turn (the one with the link) is not visible, while the turns before and after it render normally.

Investigation: I asked Claude, inside the session, to check the raw session transcript via its backend read_transcript tool. The full text of the missing message was present in that transcript, proving the message was received and stored correctly and that this is purely a UI rendering gap, not data loss.

What should happen: every user and assistant turn that exists in the backend transcript should render in the chat log UI.

Related: likely the same root-cause class as #42890 (backend/transcript data intact, UI fails to render it) but a different manifestation - partial turn loss rather than truncation to a single last message.

What Should Happen?

Every user and assistant turn that exists in the backend session transcript should render in the Cowork chat log UI. No turns should silently disappear from the display.

Error Messages/Logs

Steps to Reproduce

Have an extended Cowork session with several turns, including at least one user message that contains a pasted link. Continue the conversation for several more turns after that message. Scroll back through the session's chat log in the Cowork UI. Observe that the earlier user turn containing the link is not visible, while the turns immediately before and after it render normally. Optionally, ask Claude within the session to call its backend read_transcript tool and confirm the missing message's full text is present in the stored transcript, showing the data exists server-side and the gap is UI-only.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

N/A - reported from Claude Cowork (desktop app), not the Claude Code CLI

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

_No response_