Sessions index stops updating, breaking --resume

Bug Description

The sessions-index.json file that --resume relies on stopped being updated around late January / early February 2026. Session JSONL data files continue to be written correctly, but the index is never appended to — making --resume unable to find any recent sessions.

Reproduction

1. Run multiple Claude Code sessions over a period of days/weeks
2. Check ~/.claude/projects/<project>/sessions-index.json — the newest entry will be weeks old
3. Compare against actual .jsonl session files in the same directory — many more exist than are indexed
4. claude --resume cannot find any sessions created after the index froze

Observed Behavior

• Sessions index freezes at some point and is never updated again, even across new sessions and Claude Code version updates
• Affects all project directories on the machine, not just one
• The issue persists across multiple machines
• Session .jsonl files are still written correctly — the data is there, just not indexed
• --resume with an explicit session ID may still work (bypasses index), but the interactive session picker shows nothing recent

Example (anonymized)

On one machine:

• Home project: 569 session files on disk, but index has only 344 entries
• Index last modified: Feb 4 — 279 sessions created after that date are missing
• Other project directories show the same pattern (index frozen late Jan / early Feb)

On another machine:

• Same behavior — index frozen around the same timeframe
• Multiple project directories affected

Environment

• Claude Code version: 2.1.45
• OS: macOS (Apple Silicon)
• Sessions are started both via CLI and via the SDK (--started-by daemon)

Expected Behavior

The sessions index should be updated every time a new session is created or an existing session is modified, so that --resume can always find recent sessions.

Workaround

Sessions can still be resumed by passing the full session ID directly:

claude --resume <session-uuid>

But this requires manually finding the session UUID from the filesystem, which defeats the purpose of --resume.