diff --git a/.pnp.register.mjs b/.pnp.register.mjs
index 51ca28f9ad..430a2293e2 100644
--- a/.pnp.register.mjs
+++ b/.pnp.register.mjs
@@ -1,6 +1,52 @@
-// Register the PnP ESM loader hook so that ESM imports resolve through Yarn PnP.
-// This file is intended to be used with --import (Node >= 20.6).
-import { register } from 'node:module'
+// Resolve ESM imports through Yarn PnP.
+//
+// Yarn ships .pnp.loader.mjs for use with module.register(), which runs hooks on a dedicated
+// thread — a second V8 isolate costing 50-110MB in every node process, whether or not the
+// loader does any work. registerHooks() runs synchronously in-thread instead, and PnP's own
+// resolveRequest already applies "exports" conditions, so the hook is just a lookup.
+import { registerHooks, isBuiltin, createRequire } from 'node:module'
+import { pathToFileURL, fileURLToPath } from 'node:url'
+import path from 'node:path'
 
-const loaderURL = new URL('.pnp.loader.mjs', import.meta.url)
-register(loaderURL, import.meta.url)
+const pnp = createRequire(import.meta.url)('pnpapi')
+
+registerHooks({
+  resolve(specifier, context, nextResolve) {
+    // require() is patched by .pnp.cjs, and builtins never reach the filesystem.
+    if (context.conditions.includes('require') || isBuiltin(specifier)) {
+      return nextResolve(specifier, context)
+    }
+    // Only bare specifiers need PnP. The entrypoint arrives as a path, and mocha imports test
+    // files by file:// URL; both are already resolved.
+    let url
+    if (specifier.startsWith('file://')) {
+      url = specifier
+    } else if (!context.parentURL) {
+      url = pathToFileURL(specifier).href
+    } else {
+      // Tools installed outside the project — npm, corepack — bring their own node_modules.
+      // PnP does not own those paths and refuses to resolve from them.
+      const issuer = path.dirname(fileURLToPath(context.parentURL)) + '/'
+      if (!pnp.findPackageLocator(issuer)) {
+        return nextResolve(specifier, context)
+      }
+      url = pathToFileURL(
+        pnp.resolveRequest(specifier, issuer, {
+          conditions: new Set(context.conditions),
+        })
+      ).href
+    }
+    try {
+      // Keep the resolved path in the chain so loaders registered later can still mock it.
+      return nextResolve(url, context)
+    } catch (err) {
+      // Node cannot look inside PnP's zips, nor at its __virtual__ paths, so PnP's answer is
+      // final for those. Everything else — a genuinely missing file, an error raised by
+      // another loader — is a real failure.
+      if (url.includes('/__virtual__/') || url.includes('.zip/')) {
+        return { url, shortCircuit: true }
+      }
+      throw err
+    }
+  },
+})
diff --git a/package.json b/package.json
index c9f4d13d07..4d173220e5 100644
--- a/package.json
+++ b/package.json
@@ -191,8 +191,8 @@
     "format:pug:fix": "prettier --cache --cache-location ./.cache/prettier/.prettier-cache --write --check '**/*.pug'",
     "format:jenkins": "prettier --cache --cache-location ./.cache/prettier/.prettier-cache --check '**/Jenkinsfile'",
     "format:jenkins:fix": "prettier --cache --cache-location ./.cache/prettier/.prettier-cache --write --check '**/Jenkinsfile'",
-    "format:monorepo-check": "prettier --cache --cache-location ./.cache/prettier/.prettier-cache --check '**/Jenkinsfile' 'google-ops/packer/jenkins/vm_config/init.groovy.d/*.groovy' '**/*.md' '**/docker-compose.yml' '**/docker-compose.*.yml' '.agents/**/*.js' '.agents/**/*.md' '.github/**/*.md'",
-    "format:monorepo-check:fix": "prettier --cache --cache-location ./.cache/prettier/.prettier-cache --write --check '**/Jenkinsfile' 'google-ops/packer/jenkins/vm_config/init.groovy.d/*.groovy' '**/*.md' '**/docker-compose.yml' '**/docker-compose.*.yml' '.agents/**/*.js' '.agents/**/*.md' '.github/**/*.md'",
+    "format:monorepo-check": "prettier --cache --cache-location ./.cache/prettier/.prettier-cache --check '**/Jenkinsfile' 'google-ops/packer/jenkins/vm_config/init.groovy.d/*.groovy' '**/*.md' '**/docker-compose.yml' '**/docker-compose.*.yml' '.agents/**/*.js' '.agents/**/*.md' '.github/**/*.md' .pnp.register.mjs",
+    "format:monorepo-check:fix": "prettier --cache --cache-location ./.cache/prettier/.prettier-cache --write --check '**/Jenkinsfile' 'google-ops/packer/jenkins/vm_config/init.groovy.d/*.groovy' '**/*.md' '**/docker-compose.yml' '**/docker-compose.*.yml' '.agents/**/*.js' '.agents/**/*.md' '.github/**/*.md' .pnp.register.mjs",
     "lint": "eslint --cache --cache-location ./.cache/eslint/ --max-warnings 0",
     "lint:fix": "eslint --cache --cache-location ./.cache/eslint/ --fix"
   },