Give each school its own people seed so composition no longer follows create order.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/HSchool.AppHost.Tests/SchoolSeedTests.cs

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+using System.Net.Http.Json;
+
+namespace HSchool.AppHost.Tests;
+
+/// <summary>
+/// The people seed is a school field of its own, not the school id. These tests share the
+/// AppHost, so each one starts by clearing the list.
+/// </summary>
+[Collection(AppHostCollection.Name)]
+public class SchoolSeedTests(AppHostFixture fixture)
+{
+    private static readonly DateTime Start = new(2012, 4, 3, 6, 0, 0, DateTimeKind.Utc);
+
+    [Fact]
+    public async Task SameSeed_PopulatesTheSamePeople_DifferentSeedsDoNot()
+    {
+        using var client = fixture.App.CreateHttpClient("server");
+        await SchoolApiTests.ResetAsync(client);
+
+        var first = await SchoolApiTests.CreateAsync(client, "Сид одинаковый А", Start, seed: 42);
+        var second = await SchoolApiTests.CreateAsync(client, "Сид одинаковый Б", Start, seed: 42);
+        var other = await SchoolApiTests.CreateAsync(client, "Сид другой", Start, seed: 7);
+
+        var firstYearFive = await YearFiveAsync(client, first.Id);
+        var secondYearFive = await YearFiveAsync(client, second.Id);
+        var otherYearFive = await YearFiveAsync(client, other.Id);
+
+        Assert.Equal(firstYearFive, secondYearFive);
+        Assert.NotEqual(firstYearFive, otherYearFive);
+    }
+
+    [Fact]
+    public async Task UnseededSchool_KeepsItsPeopleAfterReload()
+    {
+        using var client = fixture.App.CreateHttpClient("server");
+        await SchoolApiTests.ResetAsync(client);
+
+        var created = await SchoolApiTests.CreateAsync(client, "Сид брошен", Start);
+
+        var before = await YearFiveAsync(client, created.Id);
+
+        using var reload = await client.PostAsync("/api/dev/reload-schools", content: null, TestContext.Current.CancellationToken);
+        reload.EnsureSuccessStatusCode();
+
+        var restored = (await SchoolApiTests.GetSchoolsAsync(client)).Schools.Single(school => school.Id == created.Id);
+        Assert.Equal(created.Seed, restored.Seed);
+        Assert.Equal(before, await YearFiveAsync(client, created.Id));
+    }
+
+    [Fact]
+    public async Task PassedSeed_IsVisibleInTheSchoolList()
+    {
+        using var client = fixture.App.CreateHttpClient("server");
+        await SchoolApiTests.ResetAsync(client);
+
+        var created = await SchoolApiTests.CreateAsync(client, "Сид в списке", Start, seed: 20260819);
+
+        Assert.Equal(20260819, created.Seed);
+
+        var listed = (await SchoolApiTests.GetSchoolsAsync(client)).Schools.Single(school => school.Id == created.Id);
+        Assert.Equal(20260819, listed.Seed);
+    }
+
+    [Fact]
+    public async Task TwoUnseededSchools_ArePopulatedDifferently()
+    {
+        using var client = fixture.App.CreateHttpClient("server");
+        await SchoolApiTests.ResetAsync(client);
+
+        var first = await SchoolApiTests.CreateAsync(client, "Без сида А", Start);
+        var second = await SchoolApiTests.CreateAsync(client, "Без сида Б", Start);
+
+        Assert.NotEqual(first.Seed, second.Seed);
+        Assert.NotEqual(await YearFiveAsync(client, first.Id), await YearFiveAsync(client, second.Id));
+    }
+
+    private static async Task<(string Id, string FullName)[]> YearFiveAsync(HttpClient client, int schoolId)
+    {
+        var page = await client.GetFromJsonAsync<PeoplePage>(
+            $"/api/schools/{schoolId}/people?role=student&year=5&sort=surname&pageSize=100",
+            TestContext.Current.CancellationToken);
+        Assert.NotNull(page);
+        Assert.NotEmpty(page.People);
+        return [.. page.People.Select(person => (person.Id, person.FullName))];
+    }
+
+    private sealed record PeoplePage(IReadOnlyList<PersonRow> People);
+
+    private sealed record PersonRow(string Id, string FullName);
+}