Add event-driven state sync with ETag optimization

GameList.Tests/StateTests.cs

@@ -27,6 +27,11 @@ public class StateTests
 
         var state = await client.GetFromJsonAsync<JsonElement>("/api/state");
 
+        Assert.True(Guid.TryParse(state.GetProperty("id").GetString(), out _));
+        Assert.Equal("payload", state.GetProperty("username").GetString());
+        Assert.Equal("payload-name", state.GetProperty("displayName").GetString());
+        Assert.False(state.GetProperty("isAdmin").GetBoolean());
+        Assert.False(state.GetProperty("isOwner").GetBoolean());
         Assert.Equal(nameof(Phase.Suggest), state.GetProperty("currentPhase").GetString());
         Assert.False(state.GetProperty("votesFinal").GetBoolean());
         Assert.True(state.GetProperty("hasJoker").GetBoolean());
@@ -335,6 +340,118 @@ public class StateTests
 
         Assert.Equal(Phase.Results, phase);
     }
+
+    [Fact]
+    public async Task State_endpoint_supports_conditional_get_with_etag()
+    {
+        await using var factory = new TestWebApplicationFactory();
+        var client = factory.CreateClientWithCookies();
+        await client.RegisterAsync("etag");
+
+        var first = await client.GetAsync("/api/state");
+        first.EnsureSuccessStatusCode();
+        var firstEtag = first.Headers.ETag?.ToString();
+        Assert.False(string.IsNullOrWhiteSpace(firstEtag));
+
+        var conditional = new HttpRequestMessage(HttpMethod.Get, "/api/state");
+        conditional.Headers.TryAddWithoutValidation("If-None-Match", firstEtag);
+        var notModified = await client.SendAsync(conditional);
+
+        Assert.Equal(HttpStatusCode.NotModified, notModified.StatusCode);
+        Assert.Equal(firstEtag, notModified.Headers.ETag?.ToString());
+
+        await client.CreateSuggestionAsync("etag-changed");
+
+        var stale = new HttpRequestMessage(HttpMethod.Get, "/api/state");
+        stale.Headers.TryAddWithoutValidation("If-None-Match", firstEtag);
+        var changed = await client.SendAsync(stale);
+
+        changed.EnsureSuccessStatusCode();
+        Assert.NotEqual(firstEtag, changed.Headers.ETag?.ToString());
+    }
+
+    [Fact]
+    public async Task State_events_endpoint_emits_state_change_after_mutation()
+    {
+        await using var factory = new TestWebApplicationFactory();
+        var watcher = factory.CreateClientWithCookies();
+        await watcher.RegisterAsync("watcher");
+
+        using var streamResponse = await watcher.GetAsync("/api/events/state", HttpCompletionOption.ResponseHeadersRead);
+        streamResponse.EnsureSuccessStatusCode();
+        Assert.Equal("text/event-stream", streamResponse.Content.Headers.ContentType?.MediaType);
+
+        await using var stream = await streamResponse.Content.ReadAsStreamAsync();
+        using var reader = new StreamReader(stream);
+
+        var readyVersion = await ReadSseEventVersionAsync(reader, "ready", TimeSpan.FromSeconds(2));
+
+        var mutator = factory.CreateClientWithCookies();
+        var register = await mutator.RegisterAsync("mutator");
+        register.EnsureSuccessStatusCode();
+
+        var changedVersion = await ReadSseEventVersionAsync(reader, "state", TimeSpan.FromSeconds(3));
+        Assert.True(changedVersion > readyVersion);
+    }
+
+    [Fact]
+    public async Task Login_does_not_invalidate_state_etag()
+    {
+        await using var factory = new TestWebApplicationFactory();
+        var client = factory.CreateClientWithCookies();
+        await client.RegisterAsync("quietetag");
+
+        var first = await client.GetAsync("/api/state");
+        first.EnsureSuccessStatusCode();
+        var firstEtag = first.Headers.ETag?.ToString();
+        Assert.False(string.IsNullOrWhiteSpace(firstEtag));
+
+        var loginClient = factory.CreateClientWithCookies();
+        var login = await loginClient.LoginAsync("quietetag", "Pass123!");
+        login.EnsureSuccessStatusCode();
+
+        var conditional = new HttpRequestMessage(HttpMethod.Get, "/api/state");
+        conditional.Headers.TryAddWithoutValidation("If-None-Match", firstEtag);
+        var notModified = await client.SendAsync(conditional);
+
+        Assert.Equal(HttpStatusCode.NotModified, notModified.StatusCode);
+        Assert.Equal(firstEtag, notModified.Headers.ETag?.ToString());
+    }
+
+    private static async Task<long> ReadSseEventVersionAsync(StreamReader reader, string expectedEventName, TimeSpan timeout)
+    {
+        using var cts = new CancellationTokenSource(timeout);
+        var eventName = string.Empty;
+
+        while (true)
+        {
+            var line = await reader.ReadLineAsync(cts.Token);
+            if (line is null)
+                throw new Xunit.Sdk.XunitException("SSE stream closed unexpectedly.");
+
+            if (line.Length == 0)
+            {
+                eventName = string.Empty;
+                continue;
+            }
+
+            if (line.StartsWith("event: ", StringComparison.Ordinal))
+            {
+                eventName = line["event: ".Length..].Trim();
+                continue;
+            }
+
+            if (!line.StartsWith("data: ", StringComparison.Ordinal))
+                continue;
+
+            if (!string.Equals(eventName, expectedEventName, StringComparison.Ordinal))
+                continue;
+
+            var payload = line["data: ".Length..].Trim();
+            if (long.TryParse(payload, out var version))
+                return version;
+        }
+    }
 }