content.type === "rename" in their send action and decide their own
support story (e.g. iMessage only supports it for remote group chats).
space.send(rename("New Name")) is the canonical form; space.rename(...)
is universal sugar that delegates here.
Bidirectional: providers also surface platform rename events as inbound
Messages carrying this content; message.sender is the user who renamed
the chat (may be undefined when the platform recorded no actor).
Throws at build time if displayName is empty. Per-platform constraints
(e.g. group-only, remote-only) surface as UnsupportedError from the
provider’s send action so the canonical and sugar forms share one
error path.