lib: add late code injector

Fixes: nodejs#37440

lib/internal/bootstrap/pre_execution.js

@@ -49,6 +49,8 @@ function prepareMainThreadExecution(expandArgv1 = false) {
 
   initializeHeapSnapshotSignalHandlers();
 
+  setupLateCodeInjector();
+
   // If the process is spawned with env NODE_CHANNEL_FD, it's probably
   // spawned by our child_process module, then initialize IPC.
   // This attaches some internal event listeners and creates:
@@ -456,6 +458,30 @@ function loadPreloadModules() {
   }
 }
 
+function setupLateCodeInjector() {
+  let resolvedAgent;
+  try {
+    resolvedAgent = require.resolve(process.env.Agent);
+  } catch(err) {
+  }
+
+  const signal = process.env.Signal;
+
+  function handler() {
+    const {
+      execute,
+    } = require(resolvedAgent);
+
+    execute();
+
+    delete require.cache[resolvedAgent];
+  }
+
+  if (signal && resolvedAgent) {
+    process.on(signal, handler);
+  }
+}
+
 module.exports = {
   patchProcessObject,
   setupCoverageHooks,