[BUG] CLI Returning to a previous agent session loses all conversation context with no compression/summary

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?

When I navigate away from an active agent session (back to the agents list), work in a different agent, and then return to the original session after an extended period, Claude has no memory of the prior conversation. There is no compressed or summarized context — it behaves as if the session is completely fresh, despite hours of prior conversation.

Expected behavior: Claude should retain context from the prior conversation, either in full or as a compressed summary.

Actual behavior: Claude has zero context from the prior conversation. No summary, no compression — it acts as a brand new session. The chat UI only shows my last sent message — all prior messages and Claude's responses are gone.

Impact: Hours of collaborative work (decisions made, code explored, plans discussed) are lost, forcing the user to re-establish all context from scratch.

What Should Happen?

Claude should retain context from the prior conversation, either in full or as a compressed summary.

Error Messages/Logs

Steps to Reproduce

1. Start an agent session in CLI and have a substantial conversation (mine was several hours of work)
2. Navigate back to the agents list (← for agents)
3. Start or open a different agent session and do some work
4. Leave the original session idle for ~10 hours
5. Navigate back to the agents list
6. Re-open the original agent session

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.232

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

cmux terminal