fix(mdviewer): clear sync highlights when cursor sync is toggled off

When the user disables cursor sync via the toolbar button, any existing
highlights on both sides should be cleared:
- Viewer: clear .cursor-sync-highlight element (paragraph class, br-line
  span, or code-line overlay) and reset _lastHighlight tracking
- CM: remove the cm-cursor-sync-highlight line class

Author: abose

src-mdviewer/src/bridge.js

@@ -537,6 +537,15 @@ export function initBridge() {
 
     // Cursor sync toggle
     on("toggle:cursorSync", ({ enabled }) => {
+        // Clear any existing highlights when cursor sync is disabled
+        if (!enabled) {
+            const viewer = document.getElementById("viewer-content");
+            if (viewer) {
+                _removeCursorHighlight(viewer);
+            }
+            _lastHighlightSourceLine = null;
+            _lastHighlightTargetLine = null;
+        }
         sendToParent("mdviewrCursorSyncToggle", { enabled });
     });
 

src/extensionsIntegrated/Phoenix-live-preview/MarkdownSync.js

@@ -131,6 +131,14 @@ define(function (require, exports, module) {
                 break;
             case "mdviewrCursorSyncToggle":
                 _cursorSyncEnabled = !!data.enabled;
+                // Clear CM line highlight when cursor sync is disabled
+                if (!_cursorSyncEnabled) {
+                    const cm = _getCM();
+                    if (cm && _highlightLineHandle) {
+                        cm.removeLineClass(_highlightLineHandle, "background", "cm-cursor-sync-highlight");
+                        _highlightLineHandle = null;
+                    }
+                }
                 break;
             case "mdviewrThemeToggle":
                 sendThemeOverride(data.theme);