refactor: validate user state with zod

tests/validation.test.ts

@@ -0,0 +1,35 @@
+import { describe, expect, it } from "vitest";
+import { validateUserStateUpdate } from "../src/validation";
+
+describe("validateUserStateUpdate", () => {
+  it("returns typed data for a valid user state update", async () => {
+    const result = await validateUserStateUpdate({
+      userId: "123",
+      username: "aseph",
+      avatar: "https://example.invalid/avatar.png",
+      speaking: true,
+    });
+
+    expect(result).toEqual({
+      userId: "123",
+      username: "aseph",
+      avatar: "https://example.invalid/avatar.png",
+      speaking: true,
+    });
+  });
+
+  it("returns null for non-object input", async () => {
+    await expect(validateUserStateUpdate("bad")).resolves.toBeNull();
+  });
+
+  it("returns null for invalid field types", async () => {
+    const result = await validateUserStateUpdate({
+      userId: "123",
+      username: "aseph",
+      avatar: "https://example.invalid/avatar.png",
+      speaking: "true",
+    });
+
+    expect(result).toBeNull();
+  });
+});