fix: correct package manager selection in CLI install (#6445)

* fix: correct package manager selection in CLI install

* chore: add changeset

---------

Co-authored-by: galargh <[email protected]>

Author: aychtang

.changeset/hot-birds-cover.md

@@ -0,0 +1,5 @@
+---
+"hardhat": patch
+---
+
+Use `npm_config_user_agent` to determine what package manager to use for project creation

packages/hardhat-core/src/internal/cli/project-creation.ts

@@ -554,12 +554,24 @@ function isInstalled(dep: string) {
   return dep in allDependencies;
 }
 
+function getProjectTypeFromUserAgent() {
+  const userAgent = process.env.npm_config_user_agent;
+  // Get first part of user agent string
+  const [projectType] = userAgent?.split("/") ?? [];
+  return projectType;
+}
+
 async function isYarnProject() {
-  return fsExtra.pathExists("yarn.lock");
+  return (
+    getProjectTypeFromUserAgent() === "yarn" || fsExtra.pathExists("yarn.lock")
+  );
 }
 
 async function isPnpmProject() {
-  return fsExtra.pathExists("pnpm-lock.yaml");
+  return (
+    getProjectTypeFromUserAgent() === "pnpm" ||
+    fsExtra.pathExists("pnpm-lock.yaml")
+  );
 }
 
 async function getProjectPackageManager(): Promise<PackageManager> {