Approach B: SessionEnd hook (automatic, AI-generated)

A SessionEnd hook reads the session's JSONL file directly from ~/.claude/projects/, extracts the first few user messages as context, and calls claude -p --model claude-haiku-4-5-20251001 to generate a 4-6 word descriptive title. If Haiku is unavailable, it falls back to a sanitized version of the first message.

The hook updates both sessions-index.jsonl (for custom session browsers) and the slug field in the JSONL file (for native /resume compatibility).

// .claude/settings.json
{
  "hooks": {
    "SessionEnd": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "~/.claude/hooks/auto-rename-session.sh"
          }
        ]
      }
    ]
  }
}

Requirements: claude CLI on PATH, python3 for JSON parsing. Set SESSION_AUTORENAME=0 to disable for a specific session.

After the session ends, the /resume picker shows "fix auth middleware" instead of "2026-03-04T14:23...".