chore: import upstream snapshot with attribution

docs/plugins/rehype-prefix-base-to-root-links.mjs

@@ -0,0 +1,53 @@
+export function rehypePrefixBaseToRootLinks(options = {}) {
+  const base = normalizeBase(options.base);
+
+  return (tree) => {
+    if (!base) {
+      return;
+    }
+
+    walk(tree, (node) => {
+      if (node.tagName !== 'a') {
+        return;
+      }
+
+      const href = node.properties?.href;
+
+      if (typeof href !== 'string') {
+        return;
+      }
+
+      if (!href.startsWith('/') || href.startsWith('//') || href.startsWith(`${base}/`)) {
+        return;
+      }
+
+      node.properties.href = `${base}${href}`;
+    });
+  };
+}
+
+function walk(node, visitor) {
+  if (!node || typeof node !== 'object') {
+    return;
+  }
+
+  if (node.type === 'element') {
+    visitor(node);
+  }
+
+  if (!Array.isArray(node.children)) {
+    return;
+  }
+
+  for (const child of node.children) {
+    walk(child, visitor);
+  }
+}
+
+function normalizeBase(base) {
+  if (!base || base === '/') {
+    return '';
+  }
+
+  return base.endsWith('/') ? base.slice(0, -1) : base;
+}