pub fn chain_layers(err: &(dyn Error + 'static)) -> Vec<String>Expand description
Walk an error’s source chain top-down, returning the Display of
each layer.
No dedup: every variant is either #[error(transparent)] or wraps
its source with distinct outer text, so adjacent layers never repeat.
A new #[error("{0}")] with #[from] would break this; fix at the
variant, not here.