feat(annotations): add halo prop to text annotations

Allows disabling the paint-order stroke halo on text annotations
via `halo: false`. Useful for white text overlaid on colored chart
elements where the background-colored stroke makes text invisible.

Author: rileyhilliard

packages/core/src/types/layout.ts

@@ -505,6 +505,8 @@ export interface ResolvedLabel {
   };
   /** Background color behind the label text. */
   background?: string;
+  /** Whether to show the paint-order stroke halo. Default true. */
+  halo?: boolean;
 }
 
 // ---------------------------------------------------------------------------

packages/core/src/types/spec.ts

@@ -563,6 +563,8 @@ export interface TextAnnotation extends AnnotationBase {
   };
   /** Background color behind the text. Useful for readability over chart lines. */
   background?: string;
+  /** Whether to show the paint-order stroke halo behind text. Default true. Set false for white text on colored backgrounds. */
+  halo?: boolean;
 }
 
 /**

packages/engine/src/annotations/resolve-text.ts

@@ -121,6 +121,7 @@ export function resolveTextAnnotation(
         }
       : undefined,
     background: annotation.background,
+    halo: annotation.halo,
   };
 
   return {

packages/vanilla/src/renderers/annotations.ts

@@ -183,7 +183,7 @@ function renderAnnotation(
         rx: 2,
       });
       g.appendChild(bgRect);
-    } else if (bgColor) {
+    } else if (bgColor && annotation.label.halo !== false) {
       text.style.paintOrder = 'stroke';
       text.style.stroke = bgColor;
       text.style.strokeWidth = `${Math.round(fontSize * 0.3)}px`;