Should this return Vec<Thread>? i.e. would the metadata on Thread be useful?

We don't have to populate all the turns & items since we only do that for specific APIs (we've already documented the behavior on the Thread object)

No because sometimes we don't have them and don't need them

Also, would be nice to support pagination for consistency with our other list APIs, even though in practice you'd probably want to return everything always. Mainly because adding pagination later is a breaking change

pub struct ThreadLoadedListRequest {
    /// Opaque pagination cursor returned by a previous call.
    pub cursor: Option<String>,
    /// Optional page size; defaults to no limit
    pub limit: Option<u32>,
}

pub struct ThreadLoadedListResponse {
    pub data: Vec<String>,
    /// Opaque cursor to pass to the next call to continue after the last item.
    /// if None, there are no more items to return.
    pub next_cursor: Option<String>,
}