feat(core): highlight markdown code fences

Parse Markdown fenced code blocks as Tree-sitter injections and merge their spans back into the outer document. Resolve fence languages through the highlighter registry so aliases and registered extensions can target supported parsers.

Prefer narrower, later style spans during rendering so injected syntax can override broad Markdown raw-block styling.

Author: fcoury

src/editor.rs

@@ -4594,11 +4594,26 @@ fn directory_listing(path: &str) -> Value {
 }
 
 fn determine_style_for_position(style_info: &[StyleInfo], pos: usize) -> Option<Style> {
-    if let Some(s) = style_info.iter().find(|si| si.contains(pos)) {
-        return Some(s.style.clone());
+    let mut best = None;
+
+    for (index, style) in style_info.iter().enumerate() {
+        if !style.contains(pos) {
+            continue;
+        }
+
+        let range_len = style.end.saturating_sub(style.start);
+        let should_replace = best
+            .map(|(best_index, best_len): (usize, usize)| {
+                range_len < best_len || (range_len == best_len && index > best_index)
+            })
+            .unwrap_or(true);
+
+        if should_replace {
+            best = Some((index, range_len));
+        }
     }
 
-    None
+    best.map(|(index, _)| style_info[index].style.clone())
 }
 
 fn adjust_color_brightness(color: Option<Color>, percentage: i32) -> Option<Color> {
@@ -4805,6 +4820,48 @@ mod test {
         std::fs::remove_dir_all(root).unwrap();
     }
 
+    #[test]
+    fn style_for_position_prefers_narrower_and_later_spans() {
+        let outer_style = Style {
+            fg: Some(Color::Rgb { r: 1, g: 1, b: 1 }),
+            ..Style::default()
+        };
+        let inner_style = Style {
+            fg: Some(Color::Rgb { r: 2, g: 2, b: 2 }),
+            ..Style::default()
+        };
+        let later_style = Style {
+            fg: Some(Color::Rgb { r: 3, g: 3, b: 3 }),
+            ..Style::default()
+        };
+        let style_info = vec![
+            StyleInfo {
+                start: 0,
+                end: 20,
+                style: outer_style.clone(),
+            },
+            StyleInfo {
+                start: 5,
+                end: 10,
+                style: inner_style.clone(),
+            },
+            StyleInfo {
+                start: 5,
+                end: 10,
+                style: later_style.clone(),
+            },
+        ];
+
+        assert_eq!(
+            determine_style_for_position(&style_info, 2),
+            Some(outer_style)
+        );
+        assert_eq!(
+            determine_style_for_position(&style_info, 6),
+            Some(later_style)
+        );
+    }
+
     #[test]
     fn test_buffer_diff() {
         let contents1 = vec![" 1:2 ".to_string()];