Fix rendering subs in LLM markdown output headings

src/Elastic.Markdown/Myst/Renderers/LlmMarkdown/LlmBlockRenderers.cs

@@ -81,22 +81,10 @@ protected override void Write(LlmMarkdownRenderer renderer, HeadingBlock obj)
 	{
 		renderer.EnsureBlockSpacing();
 		renderer.WriteLine();
-
-		var headingText = ExtractHeadingText(obj);
-
 		renderer.Write(new string('#', obj.Level));
 		renderer.Write(" ");
-		renderer.WriteLine(headingText);
-	}
-
-	private static string ExtractHeadingText(HeadingBlock heading)
-	{
-		if (heading.Inline == null)
-			return string.Empty;
-		return heading.Inline.Descendants()
-			.OfType<LiteralInline>()
-			.Select(l => l.Content.ToString())
-			.Aggregate(string.Empty, (current, text) => current + text);
+		if (obj.Inline is not null)
+			renderer.WriteChildren(obj.Inline);
 	}
 }
 

tests/authoring/LlmMarkdown/LlmMarkdownOutput.fs

@@ -445,7 +445,7 @@ type ``codeblock in list`` () =
      ```
 """
 
-type ``substitions`` () =
+type ``substitutions`` () =
     static let markdown = Setup.Document """---
 sub:
   hello-world: "Hello World!"
@@ -462,7 +462,7 @@ Hello, this is a substitution: Hello World!
 This is not a substitution: {{not-found}}
 """
 
-type ``substition in codeblock`` () =
+type ``substitution in codeblock`` () =
     static let markdown = Setup.Document """---
 sub:
   hello-world: "Hello World!"
@@ -488,3 +488,18 @@ Hello, this is a substitution: {{hello-world}}
 Hello, this is a substitution: Hello World!
 ```
 """
+
+type ``substitution in heading`` () =
+    static let markdown = Setup.Document """---
+sub:
+  world: "World"
+---
+
+## Hello, {{world}}!
+"""
+
+    [<Fact>]
+    let ``renders correctly`` () =
+        markdown |> convertsToNewLLM """
+## Hello, World!
+"""