2020: Year of the Illumination?

Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.CompilationFailedException: One or more compilation failures occurred:
1qcuyjg3.lye(18,81): error CS0234: The type or namespace name 'Mvc' does not exist in the namespace 'Umbraco.Web' (are you missing an assembly reference?)
1qcuyjg3.lye(23,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(33,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(41,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(49,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(57,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(65,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(77,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(85,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(93,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(101,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
1qcuyjg3.lye(109,13): error CS0103: The name 'WriteLiteral' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(3,6): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,11): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,11): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,48): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,48): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,73): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,73): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,92): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(6,98): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,11): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,11): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,42): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,42): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,61): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,61): error CS0103: The name 'Model' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,75): error CS0103: The name 'Write' does not exist in the current context
X:\www\AfterTheWarning\AtW-U13_Live\App_Plugins\HtagGridEditor\views\headline.render.cshtml(12,81): error CS0103: The name 'Model' does not exist in the current context
   at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RuntimeViewCompiler.CompileAndEmit(RazorCodeDocument codeDocument, String generatedCode)
   at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RuntimeViewCompiler.CompileAndEmit(String relativePath)
   at Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation.RuntimeViewCompiler.OnCacheMiss(String normalizedPath)
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Razor.RazorViewEngine.CreateCacheResult(HashSet`1 expirationTokens, String relativePath, Boolean isMainPage)
   at Microsoft.AspNetCore.Mvc.Razor.RazorViewEngine.LocatePageFromPath(String executingFilePath, String pagePath, Boolean isMainPage)
   at Umbraco.Cms.Web.Website.ViewEngines.ProfilingViewEngine.GetView(String executingFilePath, String viewPath, Boolean isMainPage)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.RenderPartialCoreAsync(String partialViewName, Object model, ViewDataDictionary viewData, TextWriter writer)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.HtmlHelper.PartialAsync(String partialViewName, Object model, ViewDataDictionary viewData)
   at AspNetCore.Views_Partials_grid_editors_base.ExecuteAsync() in X:\www\AfterTheWarning\AtW-U13_Live\Views\Partials\grid\editors\base.cshtml:line 6