[FEATURE] Feature request: Programmatic session rename API (tool or slash command callable by agent)

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Problem
When building multi-session workflows (e.g., handoff skills that pass context between sessions), there's no way for an agent to programmatically rename the current session. The /rename command exists for interactive use, but agents cannot invoke slash commands.

Proposed Solution

One of:

A tool that agents can call to rename the session (user would see an approval prompt like other tool calls)
Allow agents to invoke /rename <name> programmatically
A session.rename field in the response metadata
Option 1 feels most natural — the user sees "Agent wants to rename this session to 'Agent Composer 004'" and clicks approve/deny, just like any other tool permission.

Alternative Solutions

_No response_

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

I built a handoff skill that creates structured context documents when ending a session. Each handoff includes a recommended session name with an auto-incremented number (e.g., "Agent Composer 003" → "Agent Composer 004"). When the next session picks up the handoff, it should be able to rename itself to match — but currently the agent can only show the name and hope the user copies it manually.

Additional Context

_No response_