Message exchange during active task missing from subsequent conversation context

Description

A user sent a message while Claude was actively working on a task (the conversation was mid-flow). Claude responded to that message in the correct context. However, after completing the task, Claude had no knowledge of that message or its own response — the entire exchange was absent from the conversation context.

Steps to reproduce

1. Start a task that involves multiple tool calls (e.g. a multi-step code fix + deploy)
2. While Claude is working, send a separate message on a different topic
3. Claude responds to the message appropriately at that moment
4. After the task completes, ask Claude about that message
5. Claude has no recollection of the message or its own response

Expected behavior

All messages and responses during a session should remain visible in the conversation context, including messages sent while Claude is mid-task.

Actual behavior

The message + Claude's response were present during the task but absent from the conversation context afterwards. Claude had no knowledge of the exchange when later asked about it.

Impact

Any instructions or information conveyed in a message sent during an active task may be silently lost, with Claude falsely appearing to have processed them.

Environment

• Platform: macOS (darwin 25.5.0)
• Shell: zsh