Add alpha session gate with cookie auth and login UI.

tests/HSchool.AppHost.Tests/SchoolApiTests.cs

@@ -110,6 +110,7 @@ public class SchoolApiTests(AppHostFixture fixture)
     public async Task DeleteSchool_ThatDoesNotExist_IsNotFound()
     {
         using var client = fixture.App.CreateHttpClient("server");
+        await LoginAsync(client);
 
         using var response = await client.DeleteAsync("/api/schools/999999", TestContext.Current.CancellationToken);
 
@@ -486,6 +487,7 @@ public class SchoolApiTests(AppHostFixture fixture)
     public async Task Status_ReportsTheLoopAndTheLimit()
     {
         using var client = fixture.App.CreateHttpClient("server");
+        await LoginAsync(client);
 
         var status = await client.GetFromJsonAsync<StatusResponse>("/api/status", TestContext.Current.CancellationToken);
 
@@ -510,8 +512,72 @@ public class SchoolApiTests(AppHostFixture fixture)
         Assert.True(restored.Running);
     }
 
+    internal const string TestPassword = "test-alpha";
+    internal const string TestUserName = "TestPlayer";
+
+    internal static async Task LoginAsync(HttpClient client, string userName = TestUserName)
+    {
+        using var current = await client.GetAsync("/api/session", TestContext.Current.CancellationToken);
+        if (current.IsSuccessStatusCode)
+        {
+            return;
+        }
+
+        _ = await LoginAndGetCookieAsync(client, userName);
+    }
+
+    internal static async Task<string> LoginAndGetCookieAsync(HttpClient client, string userName = TestUserName)
+    {
+        using var first = await client.PostAsJsonAsync(
+            "/api/session",
+            new { password = TestPassword, userName },
+            TestContext.Current.CancellationToken);
+
+        if (first.IsSuccessStatusCode)
+        {
+            return ExtractSessionCookie(first);
+        }
+
+        if (first.StatusCode == HttpStatusCode.Conflict)
+        {
+            userName = $"T-{Guid.NewGuid():N}"[..10];
+            using var retry = await client.PostAsJsonAsync(
+                "/api/session",
+                new { password = TestPassword, userName },
+                TestContext.Current.CancellationToken);
+            retry.EnsureSuccessStatusCode();
+            return ExtractSessionCookie(retry);
+        }
+
+        first.EnsureSuccessStatusCode();
+        return ExtractSessionCookie(first);
+    }
+
+    internal static string ExtractSessionCookie(HttpResponseMessage response)
+    {
+        if (!response.Headers.TryGetValues("Set-Cookie", out var values))
+        {
+            throw new InvalidOperationException("Login did not return a session cookie.");
+        }
+
+        foreach (var value in values)
+        {
+            if (!value.StartsWith("hschool.session=", StringComparison.OrdinalIgnoreCase))
+            {
+                continue;
+            }
+
+            var end = value.IndexOf(';');
+            return end >= 0 ? value[..end] : value;
+        }
+
+        throw new InvalidOperationException("Login did not return a session cookie.");
+    }
+
     internal static async Task ResetAsync(HttpClient client)
     {
+        await LoginAsync(client);
+
         var state = await GetSchoolsAsync(client);
 
         foreach (var school in state.Schools)