Function wrap_error_envelope 

pub fn wrap_error_envelope(
    surface_id: &str,
    message: &str,
    errors: &[ValidationError],
) -> Result<String>

Builds the payload reporting that a surface could not be produced.

Deliberately not an operations envelope. A2UI_OPERATIONS_KEY is the content sniff, so carrying it — even with an empty list — leaves a failed generation indistinguishable from a rendered one to every consumer that keys on it, history included. Upstream draws the same line: its tool returns the validated operations under one key on success and error on failure, never both, and its part converter checks error first and emits no A2UI at all.

error is therefore the human-readable message, the way upstream sends it. The specification’s structured validation fields sit alongside it rather than nested under it, since error is already the spec’s message, with the full validation list under details for callers that route on the codes.

use ag_ui_a2ui::toolkit::envelope::{is_operations_envelope, wrap_error_envelope};

let json = wrap_error_envelope("s1", "could not build the surface", &[]).unwrap();
let value: serde_json::Value = serde_json::from_str(&json).unwrap();
assert_eq!(value["error"], "could not build the surface");
assert!(!is_operations_envelope(&value));

Errors

Returns Error::Json if the error list cannot be serialized.