refactor(markdown): make processIncludes async

Resolve includes through replaceAsync and fs/promises so include
files are read without blocking the event loop while pages render
concurrently.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/node/markdownToVue.ts

@@ -138,7 +138,7 @@ export async function createMarkdownToVueRenderFn(
 
     // resolve includes
     let includes: string[] = []
-    src = processIncludes(md, srcDir, src, fileOrig, includes, cleanUrls)
+    src = await processIncludes(md, srcDir, src, fileOrig, includes, cleanUrls)
 
     const localeIndex = getLocaleForPath(siteConfig?.site, relativePath)
 

src/node/plugins/localSearchPlugin.ts

@@ -59,7 +59,7 @@ export async function localSearchPlugin(
       }
       throw e
     })
-    const src = processIncludes(md, srcDir, raw, file, [], cleanUrls)
+    const src = await processIncludes(md, srcDir, raw, file, [], cleanUrls)
     if (options._render) {
       return options._render(src, env, md)
     } else {

src/node/utils/processIncludes.ts

@@ -1,6 +1,6 @@
 import matter from 'gray-matter'
-import type { MarkdownItAsync } from 'markdown-it-async'
+import { replaceAsync, type MarkdownItAsync } from 'markdown-it-async'
-import fs from 'node:fs'
+import { readFile } from 'node:fs/promises'
 import path from 'node:path'
 import { findRegion } from '../markdown/plugins/snippet'
 import { slash, type MarkdownEnv } from '../shared'
@@ -12,12 +12,12 @@ export function processIncludes(
   file: string,
   includes: string[],
   cleanUrls: boolean
-): string {
+): Promise<string> {
   const includesRE = /<!--\s*@include:\s*(.*?)\s*-->/g
   const regionRE = /(#[^\s\{]+)/
   const rangeRE = /\{(\d*),(\d*)\}$/
 
-  return src.replace(includesRE, (m: string, m1: string) => {
+  return replaceAsync(src, includesRE, async (m: string, m1: string) => {
     if (!m1.length) return m
 
     const range = m1.match(rangeRE)
@@ -36,7 +36,7 @@ export function processIncludes(
       ? path.join(srcDir, m1.slice(m1[1] === '/' ? 2 : 1))
       : path.join(path.dirname(file), m1)
 
-    let content = fs.readFileSync(includePath, 'utf8')
+    let content = await readFile(includePath, 'utf8')
 
     if (region) {
       const [regionName] = region