Fix script tag importmap regression - preserve user content when no asp-importmap

Co-authored-by: MackinnonBuck <10456961+MackinnonBuck@users.noreply.github.com>

Author: Copilot

src/Mvc/Mvc.TagHelpers/src/ScriptTagHelper.cs

@@ -247,16 +247,25 @@ public override void Process(TagHelperContext context, TagHelperOutput output)
             var importMap = ImportMap ?? ViewContext.HttpContext.GetEndpoint()?.Metadata.GetMetadata<ImportMapDefinition>();
             if (importMap == null)
             {
-                // No importmap found, nothing to do.
-                output.SuppressOutput();
+                // No importmap found. Only suppress output if this was intended to be
+                // an automatically generated importmap (i.e., when asp-importmap was used).
+                // If the user provided explicit content without asp-importmap, let it render as-is.
+                if (ImportMap != null || context.AllAttributes.ContainsName(ImportMapAttributeName))
+                {
+                    output.SuppressOutput();
+                    return;
+                }
+                // Let the tag render as-is by continuing with normal processing
+                // Don't return here, let normal attribute copying happen
+            }
+            else
+            {
+                output.TagName = "script";
+                output.TagMode = TagMode.StartTagAndEndTag;
+                output.Attributes.SetAttribute("type", "importmap");
+                output.Content.SetHtmlContent(importMap.ToString());
                 return;
             }
-
-            output.TagName = "script";
-            output.TagMode = TagMode.StartTagAndEndTag;
-            output.Attributes.SetAttribute("type", "importmap");
-            output.Content.SetHtmlContent(importMap.ToString());
-            return;
         }
 
         // Pass through attribute that is also a well-known HTML attribute.

src/Mvc/Mvc.TagHelpers/test/ScriptTagHelperTest.cs

@@ -794,6 +794,59 @@ public void ScriptTagHelper_RendersImportMap_FromEndpoint()
         Assert.Equal(importMap.ToJson(), output.Content.GetContent());
     }
 
+    [Fact]
+    public void ScriptTagHelper_PreservesExplicitImportMapContent_WhenNoImportMapDefinition()
+    {
+        // Arrange - this simulates the user's scenario where they provide explicit importmap content
+        // without using asp-importmap attribute
+        var context = MakeTagHelperContext(
+            attributes: new TagHelperAttributeList
+            {
+                new TagHelperAttribute("type", "importmap"),
+            });
+        
+        var output = MakeTagHelperOutput("script", attributes: new TagHelperAttributeList());
+
+        var helper = GetHelper();
+        helper.Type = "importmap";
+        // No endpoint with ImportMapDefinition and no asp-importmap attribute
+        // This should NOT suppress the output, allowing user content to render
+
+        // Act
+        helper.Process(context, output);
+
+        // Assert
+        Assert.Equal("script", output.TagName); // Tag should not be suppressed
+        Assert.Equal("importmap", output.Attributes["type"].Value);
+        // The output should not be suppressed, allowing user's explicit content to render
+        Assert.False(output.IsContentModified); // Content should remain as user provided
+    }
+
+    [Fact]
+    public void ScriptTagHelper_SuppressesOutput_WhenAspImportMapAttributeUsedButNoDefinition()
+    {
+        // Arrange - this simulates using asp-importmap attribute but having no ImportMapDefinition
+        var context = MakeTagHelperContext(
+            attributes: new TagHelperAttributeList
+            {
+                new TagHelperAttribute("type", "importmap"),
+                new TagHelperAttribute("asp-importmap", null), // asp-importmap used but no value
+            });
+        
+        var output = MakeTagHelperOutput("script", attributes: new TagHelperAttributeList());
+
+        var helper = GetHelper();
+        helper.Type = "importmap";
+        // No endpoint with ImportMapDefinition but asp-importmap attribute is present
+        // This should suppress the output since it was intended to be auto-generated
+
+        // Act
+        helper.Process(context, output);
+
+        // Assert - output should be suppressed when asp-importmap is used but no definition found
+        Assert.Null(output.TagName); // Tag should be suppressed
+    }
+
     private Endpoint CreateEndpoint(ImportMapDefinition importMap = null)
     {
         return new Endpoint(