Session branch toggles missing in resume picker since 2.1.30+

Description

In the resume session picker (claude -r), sessions created via multiple /compact cycles used to show ▶ toggles for expanding their branch history. Since upgrading past 2.1.29, all sessions render as a flat list — toggles are gone.

Steps to reproduce

1. Run claude -r on a project with sessions that went through /compact multiple times
2. Observe the session list

Expected

Sessions with branches show ▶ toggle to expand/collapse history.

Actual

Flat list, no toggles on any session.

Versions tested

• 2.1.29: toggles present ✓
• 2.1.31: toggles missing ✗
• (2.1.30 not tested directly, but changelog mentions session index rewrite for that version)

Workaround

Downgrade to 2.1.29: claude install 2.1.29

Environment

• macOS 15 (Darwin 25.2.0, arm64)