Empty sessions after /clear appear in --resume picker as "(session)"

Bug Description

After using /clear in a session and then exiting, the empty post-clear session appears in the --resume / claude -r picker with the label (session). These accumulate over time and clutter the resume list, making it harder to find real sessions.

Steps to Reproduce

1. Start a Claude Code session
2. Have a conversation (so there's a real session)
3. Run /clear
4. Exit Claude (e.g., /exit or Ctrl+C)
5. Run claude -r to open the resume picker

Expected Behavior

The empty session created after /clear should not appear in the resume picker. Sessions with no user messages have nothing to resume.

Actual Behavior

A new entry labelled (session) appears in the resume picker. Each /clear + exit cycle adds another one, expanding the list with useless entries.

Suggested Fix

Either:

• Don't persist sessions that contain no user messages
• Filter out empty sessions from the --resume picker
• Don't create a new session on /clear until the user actually sends a message

Environment

• Claude Code CLI (latest)
• Linux (also likely affects macOS/Windows)