VS Code extension: sessions missing from history dropdown (not indexed in history.jsonl)

Summary

Sessions created in the VS Code extension are not appearing in the history dropdown. The session .jsonl files exist on disk but are not being appended to ~/.claude/history.jsonl, which the UI uses to populate the session list.

Environment

• Claude Code VS Code extension (latest as of 2026-05-19)
• macOS (Darwin 25.4.0)
• VS Code

Steps to reproduce

1. Use Claude Code in VS Code over multiple sessions
2. Click the history button to reveal the session dropdown
3. Observe that recent sessions are missing

Diagnostic details

• 10 session .jsonl files exist in ~/.claude/projects/<project>/
• Only 4 of those 10 are indexed in ~/.claude/history.jsonl
• 6 sessions (from May 11 through May 19) are invisible in the UI
• The last indexed session is from May 11; all sessions after that are missing from the index
• The session data is intact on disk, just not registered in the index

Possibly related actions

• Renaming sessions via the UI around the time this started
• Sessions also appearing in VS Code's native "Chat" history (possible interaction between the two systems)

Expected behavior

All sessions should appear in the history dropdown, regardless of whether they were renamed or how VS Code's native chat history interacts with them.

Actual behavior

Recent sessions are invisible in the dropdown. Data is not lost (files exist on disk), but the history.jsonl index is not being updated with new sessions.