Allow hooks or tools to set session title programmatically

Problem

There's no way to programmatically rename a session from within a conversation. The /rename command exists for manual use, but hooks and tool calls have no access to session metadata.

Use case

When resuming work on a specific project mid-session (e.g., picking from a list of active projects), the session title should reflect what's being worked on — making it easier to find and resume later. Today this requires the user to manually type /rename <project name> every time.

What I've explored

• Hooks: SessionStart, PostToolUse, etc. can run scripts and add additionalContext, but none can modify the session title.
• CLI flags: claude -n "name" works at startup but isn't available in the Desktop app or mid-session.
• SDK: renameSession() exists in the Agent SDK but isn't available from within a running session.

Proposed solution (any of these would work)

1. A tool Claude can call (e.g., SetSessionTitle) to rename the current session from within a response.
2. A hook output field (e.g., sessionTitle) that lets hook scripts set the session name.
3. Expose /rename as something hooks can trigger programmatically.

Environment

• Claude Code Desktop app (macOS)
• Also relevant to CLI users who want automated naming via hooks