Refactor npm config handling (#24565)

packages/core/test/fixture/tmpdir.ts

@@ -0,0 +1,13 @@
+import fs from "fs/promises"
+import { tmpdir as osTmpdir } from "os"
+import path from "path"
+
+export const tmpdir = async () => {
+  const dir = await fs.mkdtemp(path.join(osTmpdir(), "opencode-core-test-"))
+  return {
+    path: dir,
+    async [Symbol.asyncDispose]() {
+      await fs.rm(dir, { recursive: true, force: true })
+    },
+  }
+}