Cache statSync results in rewrite-asset-urls to reduce disk IO (#60390)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: heiskr

src/content-render/unified/rewrite-asset-urls.ts

@@ -2,6 +2,9 @@ import fs from 'fs'
 import type { Element, Node } from 'hast'
 import { visit } from 'unist-util-visit'
 
+// Process-level cache for stat results — file sizes don't change between deploys.
+const statCache = new Map<string, number | null>()
+
 // Matches any <img> tags with an href that starts with `/assets/` or '/public/'
 function isAssetOrPublicImg(node: Node): node is Element {
   return (
@@ -35,25 +38,27 @@ function getNewSrc(node: Element): string | undefined {
   const src = node.properties?.src as string
   if (!src.startsWith('/')) return
 
+  const filePath = src.slice(1)
+
+  // Check cache first — avoids repeated statSync for the same image
+  if (statCache.has(filePath)) {
+    const cachedSize = statCache.get(filePath)
+    if (!cachedSize) return
+    const split = src.split('/')
+    split.splice(2, 0, `cb-${cachedSize}`)
+    return split.join('/')
+  }
+
   try {
-    const filePath = src.slice(1)
     const stats = fs.statSync(filePath)
-    // The size is not perfect but it's good enough. The size is
-    // very fast to pick up without needing to do a deep hashing of the
-    // image's content. It's perfectly possible that someone edits an
-    // image and it's size doesn't change. Although very unlikely.
-    // The slightest change to the image is more likely to either increase
-    // or decrease the image size by at least 1 byte.
-    // Also, because of this limitation, we're not confident to cache the
-    // image more than say 24h. But in the unlikely event that someone does
-    // edit an image and the size doesn't change, there's always the
-    // escape hatch that you can soft-purge all manual CDN surrogate keys.
+    statCache.set(filePath, stats.size || null)
     if (!stats.size) return
     const hash = `${stats.size}`
     const split = src.split('/')
     split.splice(2, 0, `cb-${hash}`)
     return split.join('/')
   } catch {
+    statCache.set(filePath, null)
     console.warn(
       `Failed to get a hash for ${src} ` +
         '(This is mostly harmless and can happen with outdated translations).',