/rename: add a dynamic argument that keeps the title synced to the live session topic

Feature

Add an argument to /rename — e.g. /rename --dynamic (or /rename auto) — that, instead of setting a one-time static title, puts the session into a mode where the title continuously re-derives from the current session topic as the conversation evolves.

Use case

During long multi-step and multi-agent runs, the session/terminal title goes stale quickly. The auto-generated topic is genuinely informative at a glance, but it's a snapshot — /rename today is a manual, one-shot refresh. A dynamic mode would keep that informative signal live without re-running the command at every checkpoint.

Why this shape

Keeping it as a /rename argument means no new hook action type or CLI surface is needed — it reuses the topic-generation that already exists, just on an ongoing basis instead of once. terminalTitleFromRename would continue to govern whether the terminal tab follows along.

Note: hooks can't fill this gap today — hook actions are limited to command/prompt/agent/http/mcp_tool, none of which can enqueue a slash command, and there's no CLI entry point for /rename. So an argument on /rename itself is the natural home for this.

Possible behaviors to consider

• /rename --dynamic → enable continuous sync; /rename <name> → still pins a static title (and implicitly exits dynamic mode)
• Re-derive on natural boundaries (turn end / Stop) rather than every token, to stay cheap
• A way to turn it back off (/rename --static or just setting a manual name)

Related

• #27656 (closed) — requested programmatic/assistant-driven renaming and /rename availability in VS Code/Desktop. This request is narrower and complementary: a user-facing /rename argument for continuous topic sync.