Function verify_backend_endpoint

crates/openshell-router/src/backend.rs:458–496

(
    client: &reqwest::Client,
    route: &ResolvedRoute,
)

}

pub async fn verify_backend_endpoint(
    client: &reqwest::Client,
    route: &ResolvedRoute,
) -> Result<ValidatedEndpoint, ValidationFailure> {
    let probes = validation_probes(route);
    let Some(first) = probes.first() else {
        return Err(no_writable_protocol_failure(route));
    };

    if mock::is_mock_route(route) {
        return Ok(ValidatedEndpoint {
            url: build_provider_url(route, &route.model, first.path, false),
            protocol: first.protocol.to_string(),
        });
    }

    let headers = vec![("content-type".to_string(), "application/json".to_string())];
    let mut last_shape_failure = None;

    for probe in &probes {
        match try_validation_probe(client, route, probe, &headers).await {
            Ok(endpoint) => return Ok(endpoint),
            // A request-shape rejection means this protocol is wrong for the
            // model (e.g. a chat probe against an embeddings model), so fall
            // through to the next advertised protocol. Any other failure
            // describes the backend itself (credentials, rate limit,
            // connectivity, health) and is terminal across all protocols.
            //
            // Keep the first shape failure: it is the most-preferred protocol's
            // rejection and the most actionable error to report.
            Err(err) if err.kind == ValidationFailureKind::RequestShape => {
                last_shape_failure.get_or_insert(err);
            }
            Err(err) => return Err(err),
        }
    }

    Err(last_shape_failure.unwrap_or_else(|| no_writable_protocol_failure(route)))
}

/// Run one validation probe, retrying with its fallback body only when the
/// upstream specifically rejected `max_completion_tokens`.