pandoc 3.8+, highlight-style - Use "none" string instead of null

Pandoc 3.8 changed optSyntaxHighlighting from HighlightMethod type to Text.
The old HighlightMethod FromJSON accepted null, but Text rejects it with:
"Aeson exception: Error in $: parsing Text failed, expected String, but encountered Null"

Pass "none" string instead of null when highlight-style: none is set.

Author: cderv

src/command/render/pandoc.ts

@@ -1755,9 +1755,9 @@ function resolveTextHighlightStyle(
   const textHighlightingMode = extras.html?.[kTextHighlightingMode];
 
   if (highlightTheme === "none") {
-    // Clear the highlighting
+    // Disable highlighting - pass "none" string (not null, which Pandoc 3.8+ rejects)
     extras.pandoc = extras.pandoc || {};
-    extras.pandoc[kHighlightStyle] = null;
+    extras.pandoc[kHighlightStyle] = "none";
     return extras;
   }
 

tests/docs/smoke-all/2026/01/12/13249-highlight-style-none.qmd

@@ -0,0 +1,16 @@
+---
+title: highlight-style none test
+format:
+  html:
+    highlight-style: none
+_quarto:
+  tests:
+    html:
+      noErrors: default
+---
+
+Test that `highlight-style: none` works with Pandoc 3.8+.
+
+```python
+print("Hello, World!")
+```