Type Alias BoxedCause 

pub type BoxedCause = Box<dyn Error + Send + Sync>;

A cause from somewhere else, kept rather than flattened to text.

Boxed because the causes are genuinely unrelated types — zenoh::Error (itself a box), std::io::Error, serde_json::Error, a JoinError.

Aliased Type

pub struct BoxedCause(/* private fields */);