Preserve owning categories in public errors

errors.go

@@ -17,6 +17,31 @@ func mapPublicError(err error) error {
 	if err == nil {
 		return nil
 	}
+	var operation *usecase.OperationError
+	if errors.As(err, &operation) && operation != nil {
+		owner := publicErrorFor(operation.Category)
+		if owner != nil {
+			// Project the underlying specialized error separately, retaining both
+			// the outer operation and the original cause for Is/As callers.
+			mapped := mapPublicError(operation.Cause)
+			if errors.Is(operation.Cause, llm.ErrTransport) {
+				mapped = errors.Join(ErrTransport, mapped)
+			}
+			if errors.Is(operation.Cause, llm.ErrMalformedResponse) {
+				mapped = errors.Join(ErrMalformedResponse, mapped)
+			}
+			var internalCapacity *usecase.CapacityError
+			var internalProvider *llm.ProviderHTTPError
+			if errors.As(operation.Cause, &internalCapacity) || errors.As(operation.Cause, &internalProvider) {
+				return errors.Join(owner, mapped)
+			}
+			return errors.Join(owner, mapped, operation.Cause)
+		}
+	}
+	return mapUnownedPublicError(err)
+}
+
+func mapUnownedPublicError(err error) error {
 	var internalCapacityError *usecase.CapacityError
 	if errors.As(err, &internalCapacityError) && internalCapacityError != nil &&
 		strings.TrimSpace(internalCapacityError.BackendID) != "" {