Feature: Allow commands/skills to rename the current session

Problem

Custom commands and skills (defined in .claude/commands/) have no way to programmatically rename the current session. The /name REPL command exists for interactive use, but it's not exposed as a tool that commands can invoke during execution.

This limits the usefulness of commands that establish a clear working context. For example, a /fix-issue 42 command that reads a GitHub issue and implements it would benefit from automatically naming the session #42 Fix widget overflow — making it instantly identifiable in the session list. Today, the user has to manually run /name afterwards, which breaks the flow.

Proposed Solution

Expose a SessionRename tool (or similar) that commands, skills, and agents can call to set the session name:

SessionRename(name: "#42 Fix widget overflow")

Alternatively, this could be a lighter-weight mechanism like a special output directive that the harness interprets, but a proper tool would be the most consistent approach.

Use Cases

• Issue workflows: A /fix-issue <number> command fetches the issue title and renames the session to #42 <title>, so the session list becomes a natural task board
• Feature branches: A command that creates a worktree could name the session after the branch
• Long-running tasks: A /deploy staging command could name the session deploy → staging for easy identification
• Any custom workflow where the command knows a better name than the default timestamp

Current Workaround

None — /name is only available interactively and cannot be called from within a tool/command execution context. The best approximation is printing "Run /name #42 to rename this session" as output, which requires manual user action.