fix: remove unsafe remove of install folder

sources/Engine.ts

@@ -18,7 +18,7 @@ import {SupportedPackageManagers, SupportedPackageManagerSet} from './types';
 export type PreparedPackageManagerInfo = Awaited<ReturnType<Engine[`ensurePackageManager`]>>;
 
 export function getLastKnownGoodFile(flag = `r`) {
-  return fs.promises.open(path.join(folderUtils.getInstallFolder(), `lastKnownGood.json`), flag);
+  return fs.promises.open(path.join(folderUtils.getCorepackHomeFolder(), `lastKnownGood.json`), flag);
 }
 
 export async function getJSONFileContent(fh: FileHandle) {

sources/corepackUtils.ts

@@ -109,11 +109,9 @@ export async function installVersion(installTarget: string, locator: Locator, {s
   const {version, build} = locatorReference;
 
   const installFolder = path.join(installTarget, locator.name, version);
-  const corepackFile = path.join(installFolder, `.corepack`);
 
-  // Older versions of Corepack didn't generate the `.corepack` file; in
-  // that case we just download the package manager anew.
-  if (fs.existsSync(corepackFile)) {
+  if (fs.existsSync(installFolder)) {
+    const corepackFile = path.join(installFolder, `.corepack`);
     const corepackContent = await fs.promises.readFile(corepackFile, `utf8`);
     const corepackData = JSON.parse(corepackContent);
 
@@ -172,14 +170,6 @@ export async function installVersion(installTarget: string, locator: Locator, {s
     hash: serializedHash,
   }));
 
-  // The target folder may exist if a previous version of Corepack installed
-  // it but didn't create the `.corepack` file. In this case we need to
-  // remove it first.
-  await fs.promises.rm(installFolder, {
-    recursive: true,
-    force: true,
-  });
-
   await fs.promises.mkdir(path.dirname(installFolder), {recursive: true});
   try {
     await fs.promises.rename(tmpFolder, installFolder);

sources/folderUtils.ts

@@ -6,7 +6,12 @@ import process           from 'process';
 
 import type {NodeError}  from './nodeUtils';
 
-export function getInstallFolder() {
+/**
+ * If the install folder structure changes then increment this number.
+ */
+const INSTALL_FOLDER_VERSION = 1;
+
+export function getCorepackHomeFolder() {
   return (
     process.env.COREPACK_HOME ??
     join(
@@ -18,6 +23,13 @@ export function getInstallFolder() {
   );
 }
 
+export function getInstallFolder() {
+  return join(
+    getCorepackHomeFolder(),
+    `v${INSTALL_FOLDER_VERSION}`,
+  );
+}
+
 export function getTemporaryFolder(target: string = tmpdir()) {
   mkdirSync(target, {recursive: true});