[BUG] /resume shows only stale sessions — recent sessions missing (v2.1.89, no sessions-index.json)

Summary

/resume inside an active session shows only sessions from ~5+ days ago. Recent sessions (including today's) do not appear in the picker, even though session .jsonl files exist and are valid on disk.

Environment

• OS: macOS (Darwin 25.3.0, arm64)
• Claude Code: v2.1.89
• Mode: --dangerously-skip-permissions (also reproduced in default mode)

Steps to Reproduce

1. Run multiple sessions over several days (cd ~/ && claude --dangerously-skip-permissions)
2. Accumulate 200+ session files in ~/.claude/projects/-Users-<user>/
3. In a new session, type /resume
4. Only sessions from ~5 days ago appear — today's 6 sessions and recent days are missing

Observed Behavior

• /resume picker shows ~5-10 old sessions, none from the last few days
• ~/.claude/sessions-index.json does not exist — appears to never have been created
• ~/.claude/sessions/ only contains entries for currently active sessions (cleaned up on exit)
• All 215 .jsonl session files are intact with valid data (verified via grep/python)
• claude --resume <session-id> with a direct ID works correctly

Expected Behavior

/resume should list all recent sessions sorted by last activity, regardless of how many total sessions exist.

Investigation

This appears related to the previously reported (and closed) #26123, where sessions-index.json stopped being written. In v2.1.89, the index file doesn't exist at all, suggesting the underlying indexing mechanism is still broken or was never fully fixed.

Verification commands

# Session files exist and are recent
ls -lt ~/.claude/projects/-Users-*//*.jsonl | head -10

# No index file
ls ~/.claude/sessions-index.json  # not found

# Direct resume works
claude --resume <any-session-id>  # works fine

Workaround

Use claude --resume <session-id> with the session ID directly. Session IDs can be found from filenames in ~/.claude/projects/.