[BUG] Session context truncated at version boundary after /exit when reopening in 2.1.85 #39856

Preflight Checklist

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

What's Wrong?

After ending a session with /exit and reopening Claude Code in 2.1.85, the model's context is truncated at the previous version boundary — it can see messages from the most recent version segment but not from earlier segments. The session JSONL and parentUuid chain are fully intact.

Confirmed with /context: in 2.1.84 the session had 133.9k tokens (67%) of message context. After /exit + reopen in 2.1.85, context dropped to 5.1k tokens (2.5%) — only the 2.1.84 and 2.1.85 messages were visible; all prior history was gone. After downgrading back to 2.1.84, the full context and history became visible again.

The model self-diagnosed: "The previous session's context was not carried over. I only knew what was in the git log shown at conversation start. The autocompact buffer didn't transfer either — this is a fresh session."

What Should Happen?

Reopening a session in 2.1.85 should load the full conversation history from the session JSONL, not just the most recent version segment. The parentUuid chain exists and is intact — it just needs to be traversed fully.

Error Messages/Logs

None - there is simply a lack of context. Diagnosed via /context showing 5.1k tokens vs expected 133.9k tokens.

Steps to Reproduce

1. Run a long session in version 2.1.81 (or any version before 2.1.84)
2. End it with /exit
3. Open Claude Code in the same working directory in 2.1.84 — verify with /context that full history is present
4. End it with /exit
5. Update to 2.1.85 and open Claude Code in the same working directory
6. Run /context — context is now near-empty; ask about prior work — model has no knowledge of it

Reproduced in two separate sessions across two projects. Downgrading to 2.1.84 restores full context.

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

2.1.84

Claude Code Version

2.1.85

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Kitty

Additional Information

Related prior fixes that did not address this case:

• 2.1.83: "Fixed SDK session history loss on resume caused by hook progress/attachment messages forking the parentUuid chain" — parentUuid chain verified intact in our sessions.
• 2.1.83: "Fixed remote sessions forgetting conversation history after a container restart" — applies to remote sessions only.