Add payload serializer guardrails

RpgRoller.Tests/Api/ResponseCompressionApiTests.cs

@@ -0,0 +1,27 @@
+namespace RpgRoller.Tests;
+
+public sealed class ResponseCompressionApiTests : ApiTestBase
+{
+    public ResponseCompressionApiTests(WebApplicationFactory<Program> factory) : base(factory)
+    {
+    }
+
+    [Fact]
+    public async Task AuthenticatedJsonResponses_EnableGzipCompression()
+    {
+        using var factory = CreateFactory();
+        using var client = factory.CreateClient(new() { AllowAutoRedirect = false });
+
+        await RegisterAsync(client, "gm-compress", "Password123", "GM");
+        await LoginAsync(client, "gm-compress", "Password123");
+        _ = await PostAsync<CreateCampaignRequest, CampaignSummary>(client, "/api/campaigns", new("Compressed", "d6"));
+
+        var request = new HttpRequestMessage(HttpMethod.Get, "/api/campaigns");
+        request.Headers.Add("Accept-Encoding", "gzip");
+
+        var response = await client.SendAsync(request);
+
+        response.EnsureSuccessStatusCode();
+        Assert.Contains("gzip", response.Content.Headers.ContentEncoding);
+    }
+}