fix(test/build): clean dist before bundling vitest

bundleVitest copied vitest's distribution into packages/test/dist
without cleaning the directory first. When the upstream vitest
version changed, the new build emitted hashed chunks with new names
(e.g. cac.<new-hash>.js) but stale chunks from the previous version
lingered. The later brandVitest step iterates every cac.*.js chunk
looking for cac("vitest") and threw when it hit a stale chunk whose
pattern was absent or already rewritten, breaking pnpm bootstrap-cli.

Clear dist/ at the start of bundleVitest so each build starts from
a known-empty tree.

Author: fengmk2

packages/test/build.ts

@@ -436,6 +436,10 @@ async function mergePackageJson(pluginExports: Array<{ exportPath: string; shimF
 async function bundleVitest() {
   const vitestDestDir = projectDir;
 
+  // Clean dist/ so chunks from a previous vitest version don't linger.
+  // Stale hashed chunks (e.g. cac.<old-hash>.js) trip later patch steps
+  // when the new build only emits cac.<new-hash>.js.
+  await rm(distDir, { recursive: true, force: true });
   await mkdir(vitestDestDir, { recursive: true });
 
   // Get all vitest files excluding node_modules and package.json