feat: add session-rename plugin with /rename command

[ruspg]

Summary

• Adds a session-rename plugin that provides a /rename slash command
• Creates .meta.json sidecar files alongside session .jsonl files to store custom titles
• Does not modify existing session files — fully non-breaking
• Updates the plugins README table with the new entry

Closes #38173
Related: #17536 (IDE extension naming), #11408, #32593

Context

This is a highly requested feature across CLI and IDE users:

• CLI users running multiple sessions need to distinguish them in /resume (Feature request: Add session rename capability (/rename command) #38173)
• IDE users need renamable tabs when running parallel sessions (Feature Request: Renamable/Named Sessions in Claude Code Extension #17536)
• Automation users running 10+ tmux sessions need programmatic session identification

The plugin establishes a .meta.json sidecar convention that the core CLI can adopt for:

• Displaying custom titles in /resume session picker
• Supporting --resume name for scripted session recovery
• Exposing session names to hooks and status lines

How it works

1. User runs /rename Fix auth bug in any session
2. The command locates the current session .jsonl file in ~/.claude/projects/
3. It writes a {sessionId}.meta.json with the custom title and timestamp
4. Future /resume integration can read .meta.json to display custom names

Meta.json format

{
  "title": "Fix auth bug",
  "renamed_at": "2026-03-24T09:00:00Z",
  "auto_title": null
}

Test plan

• Install plugin and run /rename My custom name
• Verify .meta.json is created alongside the session .jsonl
• Run /rename without arguments — should prompt for a name
• Run /rename again to verify it updates existing .meta.json

Future integration path (for core CLI)

Based on community feedback in #17536:

1. /resume reads .meta.json and shows custom title when available
2. claude --session-name X flag writes .meta.json at session start
3. CLAUDE_CODE_SESSION_ID env var exposed in tool-call shell
4. IDE extension reads .meta.json for tab naming

[pwinnski]

There's already a /rename command.

[ruspg]

Closing — /rename is already a built-in command in Claude Code CLI with full integration into /resume, terminal tab titles, VS Code session list, and context compaction. The feature requested in #38173 already exists. Apologies for the noise!