fix: resolve shortcodes inside math expressions

Shortcodes inside inline and display math (e.g., `$5 + {{< meta five >}}$`)
were not being resolved, producing hex-encoded UUID placeholders in output.

Two gaps in the pipeline both lacked Math node handlers: the UUID restoration
walker in readqmd.lua and the shortcode resolution filter in shortcodes.lua.

Fixes #14255

Author: cderv

src/resources/filters/customnodes/shortcodes.lua

@@ -325,6 +325,10 @@ function shortcodes_filter()
       doc = _quarto.ast.walk(doc, {
         Shortcode = inline_handler,
         RawInline = code_handler,
+        Math = function(el)
+          el.text = apply_code_shortcode(el.text)
+          return el
+        end,
         Image = function(el)
           el = attr_handler(el)
           el.src = apply_code_shortcode(el.src)

src/resources/pandoc/datadir/readqmd.lua

@@ -192,6 +192,7 @@ local function readqmd(txt, opts)
     Code = unshortcode_text,
     RawInline = unshortcode_text,
     RawBlock = unshortcode_text,
+    Math = unshortcode_text,
     Header = filter_attrs,
     Span = filter_attrs,
     Div = filter_attrs,

tests/docs/smoke-all/shortcodes/shortcode-math.qmd

@@ -0,0 +1,17 @@
+---
+title: Shortcode in Math
+format: html
+five: 5
+_quarto:
+  tests:
+    html:
+      ensureFileRegexMatches:
+        - ['5 \+ 5']
+        - ['b58fc729|7B7B3C']
+---
+
+Inline: $5 + {{< meta five >}}$
+
+Display: $$5 + {{< meta five >}}$$
+
+Plain: {{< meta five >}}