[BUG] VS Code: opening a session whose transcript exceeds 2 GiB crash-loops the extension host

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?

Opening a long-running session from the Claude Code panel crashes the VS Code extension host about 15 s after the webview sends get_session_request with purpose: "transcript_open". VS Code restarts the host, the panel restores the same session, and it crashes again: "Extension host terminated unexpectedly 3 times within the last 5 minutes". Downgrading the extension did not help. Other sessions open normally.

The session transcript ~/.claude/projects/<project>/<session-id>.jsonl is 2.26 GB. The session kept working while it stayed open and broke on the first reopen after a VS Code restart. More than half of the file (1.3 GB) is duplicated rows from #92089, so long sessions reach this size much sooner than expected.

What Should Happen?

Opening or resuming a session should not need the whole transcript (the model only needs the part after the last compact_boundary), or at least it should fail gracefully for that one session instead of taking down the extension host. The panel should not keep restoring a session that just crashed the host.

Error Messages/Logs

main.log:      Extension host with pid 8144 exited with code: 0, signal: unknown.
renderer.log:  Extension host (LocalProcess pid: 8144) terminated unexpectedly.
Claude VSCode.log, right before each crash:
  Received message from webview: {"type":"request","request":{"type":"get_session_request","sessionId":"…","purpose":"transcript_open"}}

Steps to Reproduce

1. Have a session whose .jsonl transcript is over 2 GiB (for example a long session with many auto-compactions, see #92089).
2. Open it from the Claude Code panel in VS Code.
3. After ~15 s the extension host crashes, restarts, the panel reopens the session, and the loop repeats.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.288

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

Workaround: copy the lines from the last compact_boundary to the end into a new <new-uuid>.jsonl with sessionId replaced. The result is a 6.6 MB session that resumes with the same model context.

VS Code 1.140.0, Windows 11 Pro 10.0.26200, x64.