fix(Button): disabled state resolution in Button.Split context (#1134)

Author: tenphi

.changeset/fix-button-split-disabled.md

@@ -0,0 +1,9 @@
+---
+"@cube-dev/ui-kit": patch
+---
+
+Fix `Button` disabled state resolution in `Button.Split` context.
+
+- Replace `??` chain with `||` so that `isLoading={false}` no longer blocks `splitContext.isDisabled` inheritance
+- Ensure `splitContext.isDisabled` always wins over child props (a disabled split button should disable all children)
+- Fix edge case where `isDisabled={false}` with `isLoading={true}` incorrectly resulted in a clickable loading button

src/components/actions/Button/Button.tsx

@@ -400,7 +400,7 @@ export const Button = forwardRef(function Button(
     sizeProp ?? splitContext?.size ?? (type === 'link' ? 'inline' : 'medium');
 
   const isDisabled =
-    props.isDisabled ?? props.isLoading ?? splitContext?.isDisabled;
+    splitContext?.isDisabled || props.isDisabled || props.isLoading;
   const isLoading = props.isLoading;
   const isSelected = props.isSelected;