refactor: share plain object guard across config and utils

src/infra/plain-object.test.ts

@@ -0,0 +1,18 @@
+import { describe, expect, it } from "vitest";
+import { isPlainObject } from "./plain-object.js";
+
+describe("isPlainObject", () => {
+  it("accepts plain objects", () => {
+    expect(isPlainObject({})).toBe(true);
+    expect(isPlainObject({ a: 1 })).toBe(true);
+  });
+
+  it("rejects non-plain values", () => {
+    expect(isPlainObject(null)).toBe(false);
+    expect(isPlainObject([])).toBe(false);
+    expect(isPlainObject(new Date())).toBe(false);
+    expect(isPlainObject(/re/)).toBe(false);
+    expect(isPlainObject("x")).toBe(false);
+    expect(isPlainObject(42)).toBe(false);
+  });
+});

src/infra/plain-object.ts

@@ -0,0 +1,11 @@
+/**
+ * Strict plain-object guard (excludes arrays and host objects).
+ */
+export function isPlainObject(value: unknown): value is Record<string, unknown> {
+  return (
+    typeof value === "object" &&
+    value !== null &&
+    !Array.isArray(value) &&
+    Object.prototype.toString.call(value) === "[object Object]"
+  );
+}