fix(preset-algolia): keep separator highlight when reverse-highlight siblings disagree

isPartHighlighted defaulted neighbor highlight states with `|| true`, which
also overrode an existing `false` neighbor. That made both siblings always
appear highlighted, so every non-alphanumeric separator was treated as
highlighted-from-siblings regardless of its real neighbors. Use `?? true` so
the default only applies when a neighbor is missing.

Author: Aegis Dev

packages/autocomplete-preset-algolia/src/highlight/__tests__/isPartHighlighted.test.ts

@@ -16,6 +16,23 @@ describe('isPartHighlighted', () => {
     ).toEqual(true);
   });
 
+  test('does not inherit sibling state when siblings disagree', () => {
+    // The separator (index 1) sits between a highlighted ("Amazon") and a
+    // non-highlighted ("Fire") part. Since the siblings disagree, the separator
+    // must keep its own `isHighlighted` value rather than being treated as
+    // highlighted-from-siblings.
+    expect(
+      isPartHighlighted(
+        [
+          { isHighlighted: true, value: 'Amazon' },
+          { isHighlighted: false, value: ' - ' },
+          { isHighlighted: false, value: 'Fire' },
+        ],
+        1
+      )
+    ).toEqual(false);
+  });
+
   test('returns the isHighlighted value with both siblings', () => {
     expect(
       isPartHighlighted(

packages/autocomplete-preset-algolia/src/highlight/isPartHighlighted.ts

@@ -25,8 +25,8 @@ function unescape(value: string): string {
 
 export function isPartHighlighted(parts: ParsedAttribute[], i: number) {
   const current = parts[i];
-  const isNextHighlighted = parts[i + 1]?.isHighlighted || true;
-  const isPreviousHighlighted = parts[i - 1]?.isHighlighted || true;
+  const isNextHighlighted = parts[i + 1]?.isHighlighted ?? true;
+  const isPreviousHighlighted = parts[i - 1]?.isHighlighted ?? true;
 
   if (
     !hasLetterOrNumber.test(unescape(current.value)) &&