Named sessions from older versions not resumable in v2.1.x #23933

Description

Named sessions created under older Claude Code versions cannot be resumed in v2.1.34. The --resume flag (by custom title or UUID) opens the session picker UI with empty results, even though the session data is intact on disk and correctly referenced in sessions-index.json.

Steps to Reproduce

1. Have named sessions created under an older Claude Code version (pre-2.x)
2. Upgrade to Claude Code v2.1.34
3. Run claude --resume <session-name> or claude --resume <session-uuid>
4. The "Resume Session" picker UI appears but shows no matching results

Expected Behavior

The session should resume, or at minimum appear in the picker results.

Actual Behavior

The picker UI opens with an empty list — no sessions are shown despite typing the exact custom title.

Investigation Findings

• The session .jsonl file exists on disk (971KB, 565 lines, valid JSON)
• The sessions-index.json contains the correct entry with customTitle, sessionId, and fullPath
• The first line of the session file has type: "file-history-snapshot" — same structure as working sessions
• 30 session files exist on disk but only 8 are in the index, suggesting possible index truncation
• Newly created sessions (created and renamed in v2.1.34) resume correctly
• The broken session was created Jan 5, 2026 and last modified Jan 19, 2026

Environment

• Claude Code version: 2.1.34
• OS: Ubuntu Linux 6.8.0-100-generic
• Shell: zsh

Workaround

None found. The session data is intact but inaccessible through the resume UI.