Function analyse_open_shape 

pub fn analyse_open_shape<'a>(
    body: &'a Block,
    local_agents: &HashSet<String>,
) -> WsOpenShape<'a>

Analyse a from websocket on open body: find the top-level agent transfers of the connection binding (a let _ <- Agent(key).m(…, connection) statement). A transfer nested in a conditional is deliberately not counted — the host DO must be statically resolvable.