diff --git a/action.yml b/action.yml
index 380280d..2b5d045 100644
--- a/action.yml
+++ b/action.yml
@@ -133,5 +133,5 @@ outputs:
     description: "GitHub App slug"
 runs:
   using: "node24"
-  main: "dist/bootstrap.js"
-  post: "dist/post.js"
+  main: "dist/bootstrap.cjs"
+  post: "dist/post.cjs"
diff --git a/bootstrap.js b/bootstrap.js
index 0619965..123b816 100644
--- a/bootstrap.js
+++ b/bootstrap.js
@@ -1,7 +1,7 @@
-// Enable env-based proxy support before loading the main bundle (unless caller explicitly set NODE_USE_ENV_PROXY)
+// Enable env-based proxy support unless caller explicitly set NODE_USE_ENV_PROXY
 if (process.env.NODE_USE_ENV_PROXY == null) {
-  process.env.NODE_USE_ENV_PROXY = "1";
+  process.env.NODE_USE_ENV_PROXY = 1;
 }
 
-// Defer to original main entry (dynamic import ensures above code runs first)
-await import("./main.js");
+// Import main after environment prepared. Using dynamic import so this executes first even when bundled.
+import("./main.js");
diff --git a/package.json b/package.json
index 76a73cb..2123f18 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,7 @@
     "node": ">=24.4.0"
   },
   "scripts": {
-  "build": "esbuild bootstrap.js main.js post.js --bundle --outdir=dist --format=esm --platform=node --packages=bundle",
+  "build": "esbuild bootstrap.js main.js post.js --bundle --outdir=dist --out-extension:.js=.cjs --platform=node --packages=bundle",
     "test": "c8 --100 ava tests/index.js",
     "coverage": "c8 report --reporter html",
     "postcoverage": "open-cli coverage/index.html"