Session list sorts by file mtime, which AI-title backfill clobbers — unrelated old sessions jump to "now"

Summary

The session/resume browser orders sessions by transcript file mtime. But Claude Code appends lines to old *.jsonl transcripts after a session is over — notably {"type":"ai-title",...} (and {"type":"mode",...}) when it generates/backfills the AI titles shown in that very list. Each append bumps the file's mtime to "now."

Result: opening or working in one session triggers a batch of title writes across several other, untouched sessions, so they all leap to the top of the list with a near-identical recent timestamp (e.g. five sessions all reading "8m"). This makes "which session did I last actually work in?" very hard to answer.

Repro

1. Have several older sessions in a project.
2. Start/resume work so titles get (re)generated.
3. Observe multiple unrelated sessions now showing the same recent relative time at the top of the list.

Evidence

In the affected transcripts, the last line is type: ai-title / type: mode (no timestamp field), while the newest line that actually has a timestamp is hours or days older. The file mtime tracks the title append, not real activity. Ranking the same sessions by their newest real-message timestamp produces a correct, stable order that differs sharply from the mtime order.

Expected

Order the list by the newest real message timestamp in each transcript (ignoring ai-title / summary / mode lines), or store a dedicated "last activity" field, so metadata writes don't reorder the list.

Environment

• Claude Code in the VS Code extension
• Linux