Merge phase 26 school seed.

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

docs/design/people.md

@@ -261,10 +261,14 @@ Protocol ← Server → Simulation → People → Content
 
 ### Детерминизм
 
-Генерация детерминирована от **сида**, сид лежит в файле школы. Один сид + одна карта + один набор
+Генерация детерминирована от **сида**. Сид — своё поле школы, не её идентификатор: при создании
+его бросает сервер, либо его передают в `POST /api/schools`. Он лежит в файле людей и виден в
+списке школ и на экране школы, чтобы им можно было поделиться. Один сид + одна карта + один набор
 имён + один родной язык = одна и та же школа, всегда. Если родной язык при создании не указан,
 его выбирает тот же сид — повтор без поля даёт тот же язык.
 
+Существующие школы не перебрасываются: они продолжают жить с числом, уже записанным в файле людей.
+
 Сид у каждой семьи свой, выведенный из школьного: добавление тринадцатой семьи не должно менять
 первые двенадцать. Иначе тест на генератор ломается от любой правки порядка.
 
@@ -389,7 +393,7 @@ Protocol ← Server → Simulation → People → Content
 | Падежи | Правило по умолчанию (код), явная таблица как исключение (данные) |
 | Имена и язык UI | Независимы |
 | Библиотека | `HSchool.People`: зависит от Content, не знает Arch и ASP.NET |
-| Детерминизм | Сид в сейве, свой сид на семью; родной язык — часть входа |
+| Детерминизм | Свой сид школы (не id), в сейве и в API; свой сид на семью; родной язык — часть входа |
 | Просмотр | Панель в оболочке менеджера, вкладкой рядом с картой; не отдельный экран |
 | Список | Фильтры, сортировки, пейджинг; в строке — только лёгкие поля |
 | Транспорт списка | HTTP по опубликованному снимку ростера |

docs/phases/26-school-seed.md

@@ -15,20 +15,20 @@
 
 ## Задачи
 
-- [ ] При создании школы сид берётся из генератора случайных чисел сервера, а не из id
-- [ ] `POST /api/schools` принимает необязательный `seed`; передали — берётся он, нет — бросается
-- [ ] Сид виден: в ответе `GET /api/schools` и на экране школы, чтобы его можно было переслать
-- [ ] Существующие школы не меняются: сид читается из файла людей, как и сейчас
-- [ ] Тесты хоста, которым нужен предсказуемый состав, передают сид явно, а не полагаются на
+- [x] При создании школы сид берётся из генератора случайных чисел сервера, а не из id
+- [x] `POST /api/schools` принимает необязательный `seed`; передали — берётся он, нет — бросается
+- [x] Сид виден: в ответе `GET /api/schools` и на экране школы, чтобы его можно было переслать
+- [x] Существующие школы не меняются: сид читается из файла людей, как и сейчас
+- [x] Тесты хоста, которым нужен предсказуемый состав, передают сид явно, а не полагаются на
       порядок создания
-- [ ] `docs/protocol.md` и [`../design/people.md`](../design/people.md) правятся тем же коммитом
+- [x] `docs/protocol.md` и [`../design/people.md`](../design/people.md) правятся тем же коммитом
 
 ## Тесты, без которых фаза не закрыта
 
-- [ ] Две школы, созданные с одним сидом, населены одинаково; с разными — по-разному
-- [ ] Школа, созданная без сида, после перезапуска поднимает тот же состав
-- [ ] Старый сейв, где сид совпадал с id, грузится и состав не меняется
-- [ ] Переданный сид виден в списке школ
+- [x] Две школы, созданные с одним сидом, населены одинаково; с разными — по-разному
+- [x] Школа, созданная без сида, после перезапуска поднимает тот же состав
+- [x] Старый сейв, где сид совпадал с id, грузится и состав не меняется
+- [x] Переданный сид виден в списке школ
 
 ## Критерий готовности
 

docs/phases/README.md

@@ -110,6 +110,6 @@
 | [23. Пример мода](23-example-pack.md) | ⬜ | Настоящая папка вместо документов в памяти |
 | [24. Числа поведения](24-behavior-numbers.md) | ✅ | Веса целей в `BehaviorDef`, а не в коде |
 | [25. Золотые файлы](25-golden-fixtures.md) | ✅ | Отпечаток ростера, старый сейв, кривая голода, нехватка учителей |
-| [26. Свой сид](26-school-seed.md) | 🔄 | Состав школы перестаёт зависеть от порядка создания |
+| [26. Свой сид](26-school-seed.md) | ✅ | Состав школы перестаёт зависеть от порядка создания |
 | [27. Версия сейва и дамп](27-serviceability.md) | ✅ | Формат читается, внутрь школы можно заглянуть |
 | [28. Тесты экранов](28-screen-tests.md) | ⬜ | DOM-окружение и логика клиента под тестом |

docs/protocol.md

@@ -32,6 +32,8 @@ the wire format is unambiguous, and the client formats it back in UTC.
 
 Everything the main menu needs in one request. `schoolWeekDays` is 5–7 working days counted
 from Monday (five is Mon–Fri; six adds Saturday). It is a school rule, not a catalog def.
+`seed` is the roster generator seed: it is not the school id. Share it to recreate the same
+people; it does not change on a living school.
 
 ```json
 {
@@ -40,7 +42,7 @@ from Monday (five is Mon–Fri; six adds Saturday). It is a school rule, not a c
   "gameMinutesPerRealSecond": 5,
   "schoolWeekDays": 5,
   "schools": [
-    { "id": 1, "name": "Гимназия №14", "gameTime": "2012-03-31T07:35:00Z", "running": false, "speedIndex": 1, "modIds": ["core"] }
+    { "id": 1, "name": "Гимназия №14", "gameTime": "2012-03-31T07:35:00Z", "running": false, "speedIndex": 1, "modIds": ["core"], "seed": 1847291 }
   ]
 }
 ```
@@ -117,7 +119,8 @@ Body:
   "modIds": [],
   "map": null,
   "nameSetId": "Slavic",
-  "nativeLanguage": null
+  "nativeLanguage": null,
+  "seed": null
 }
 ```
 
@@ -129,6 +132,8 @@ the same catalog. Omit `map` (or send `null`) to use that pack set's default lay
 `Slavic`). Unknown ids return `400` `unknown-name-set`.
 `nativeLanguage` is a skill from that set's `nativeLanguages`. Omit it (or send `null`) to pick
 one from the school seed. An id that is not in the set returns `400` `unknown-native-language`.
+`seed` is an optional integer. Send it to reproduce a known school; omit it (or send `null`) and
+the server rolls one. Existing saves keep the seed already stored in the people file.
 
 | Status | Meaning |
 | --- | --- |

src/HSchool.Client/src/i18n/strings.ts

@@ -57,6 +57,10 @@ const ru = {
   editMap: 'Редактировать карту',
   mapDefaultHint: 'Будет использована карта по умолчанию.',
   mapEditedHint: 'Карта изменена.',
+  schoolSeed: 'Сид {seed}',
+  schoolSeedLabel: 'Сид',
+  schoolSeedHint: 'Необязательно. Чужой сид даёт ту же школу; пустое поле бросает свой.',
+  schoolSeedInvalid: 'Сид должен быть целым числом.',
   resetMap: 'Сбросить к умолчанию',
   done: 'Готово',
   editorStructure: 'Структура',
@@ -270,6 +274,10 @@ const en: Messages = {
   editMap: 'Edit map',
   mapDefaultHint: 'The default map will be used.',
   mapEditedHint: 'The map has been edited.',
+  schoolSeed: 'Seed {seed}',
+  schoolSeedLabel: 'Seed',
+  schoolSeedHint: 'Optional. A shared seed recreates the same people; leave blank to roll one.',
+  schoolSeedInvalid: 'The seed must be a whole number.',
   resetMap: 'Reset to default',
   done: 'Done',
   editorStructure: 'Structure',

src/HSchool.Client/src/net/api.ts

@@ -10,7 +10,10 @@ export interface School {
   readonly gameTime: string;
   readonly running: boolean;
   readonly speedIndex: number;
+  readonly speedIndex: number;
   readonly modIds?: readonly string[];
+  /** Roster generator seed. Independent of `id`; share it to recreate the same people. */
+  readonly seed: number;
 }
 
 export interface SchoolsResponse {
@@ -53,6 +56,7 @@ export interface CreateSchoolOptions {
   readonly map?: MapLayout;
   readonly nameSetId?: string;
   readonly nativeLanguage?: string;
+  readonly seed?: number;
 }
 
 export async function createSchool(
@@ -70,6 +74,7 @@ export async function createSchool(
       map: extras.map ?? null,
       nameSetId: extras.nameSetId ?? null,
       nativeLanguage: extras.nativeLanguage ?? null,
+      seed: extras.seed ?? null,
     }),
   });
 }

src/HSchool.Client/src/style.css

@@ -125,6 +125,21 @@ body {
   font-weight: 600;
 }
 
+.screen__heading {
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+  min-width: 0;
+}
+
+.screen__seed {
+  margin: 0;
+  color: var(--text-muted);
+  font-size: 13px;
+  font-weight: 400;
+  user-select: all;
+}
+
 .screen__actions {
   margin-left: auto;
 }

src/HSchool.Client/src/ui/createSchoolDialog.ts

@@ -64,6 +64,12 @@ export function createSchoolDialog(options: CreateSchoolOptions): Promise<School
     nativeLanguageId = nativeSelect.value === '' ? null : nativeSelect.value;
   });
 
+  const seedLabel = el('span', { class: 'field__label' });
+  const seedInput = el('input', { class: 'input', type: 'text' });
+  seedInput.inputMode = 'numeric';
+  const seedHint = el('p', { class: 'hint' });
+  const seedField = el('label', { class: 'field' }, seedLabel, seedInput, seedHint);
+
   const mapLabel = el('span', { class: 'field__label' });
   const editMapButton = el('button', { class: 'button', type: 'button' });
   const mapHint = el('p', { class: 'hint' });
@@ -107,6 +113,7 @@ export function createSchoolDialog(options: CreateSchoolOptions): Promise<School
     nameSetField,
     nativeField,
     mapField,
+    seedField,
     error,
     el('div', { class: 'dialog__actions' }, cancelButton, submitButton),
   );
@@ -120,6 +127,7 @@ export function createSchoolDialog(options: CreateSchoolOptions): Promise<School
     randomButton.toggleAttribute('disabled', value);
     nativeRandomButton.toggleAttribute('disabled', value || languagesOf(catalog, nameSetId).length <= 1);
     editMapButton.toggleAttribute('disabled', waiting);
+    seedInput.toggleAttribute('disabled', value);
   };
 
   const showError = (message: string): void => {
@@ -238,6 +246,9 @@ export function createSchoolDialog(options: CreateSchoolOptions): Promise<School
     nativeLabel.textContent = t('nativeLanguageTitle');
     nativeRandomButton.textContent = t('randomName');
     nativeRandomButton.title = t('randomNativeTitle');
+    seedLabel.textContent = t('schoolSeedLabel');
+    seedInput.placeholder = t('schoolSeedLabel');
+    seedHint.textContent = t('schoolSeedHint');
     nameLabel.textContent = t('schoolName');
     startLabel.textContent = t('gameStart');
     mapLabel.textContent = t('mapEditorTitle');
@@ -310,6 +321,12 @@ export function createSchoolDialog(options: CreateSchoolOptions): Promise<School
       return;
     }
 
+    const seed = parseSeed(seedInput.value);
+    if (seedInput.value.trim() !== '' && seed === null) {
+      showError(t('schoolSeedInvalid'));
+      return;
+    }
+
     setBusy(true);
     options
       .create(nameInput.value.trim(), startDate, {
@@ -317,6 +334,7 @@ export function createSchoolDialog(options: CreateSchoolOptions): Promise<School
         map: currentMap,
         nameSetId: nameSetId ?? undefined,
         nativeLanguage: nativeLanguageId ?? undefined,
+        seed: seed ?? undefined,
       })
       .then((school) => modal.close(school))
       .catch((reason: unknown) => {
@@ -343,6 +361,24 @@ function mapsEqual(left: MapLayout, right: MapLayout): boolean {
   return JSON.stringify(left) === JSON.stringify(right);
 }
 
+function parseSeed(value: string): number | null {
+  const trimmed = value.trim();
+  if (trimmed === '') {
+    return null;
+  }
+
+  if (!/^-?\d+$/.test(trimmed)) {
+    return null;
+  }
+
+  const parsed = Number(trimmed);
+  if (!Number.isSafeInteger(parsed) || parsed < -2147483648 || parsed > 2147483647) {
+    return null;
+  }
+
+  return parsed;
+}
+
 function describe(reason: unknown): string {
   if (!(reason instanceof ApiError)) {
     return t('serverUnavailable');

src/HSchool.Client/src/ui/gameScreen.ts

@@ -34,6 +34,7 @@ export class GameScreen {
   private readonly root = el('section', { class: 'screen game' });
   private readonly backButton = el('button', { class: 'button', type: 'button' });
   private readonly schoolName = el('h1', { class: 'screen__title' });
+  private readonly schoolSeed = el('p', { class: 'screen__seed' });
   private readonly time = el('p', { class: 'clock__time', text: '--:--' });
   private readonly date = el('p', { class: 'clock__date' });
   private readonly weekday = el('p', { class: 'clock__weekday' });
@@ -79,6 +80,7 @@ export class GameScreen {
   private directoryToken = 0;
   private selectedId: string | null = null;
   private schoolId: number | null = null;
+  private peopleSeed: number | null = null;
   private running = false;
   private lastGameTime: Date | null = null;
   private lastSpeedIndex = 0;
@@ -102,7 +104,7 @@ export class GameScreen {
     this.skipButton.hidden = true;
 
     this.root.append(
-      el('header', { class: 'screen__header' }, this.backButton, this.schoolName),
+      el('header', { class: 'screen__header' }, this.backButton, el('div', { class: 'screen__heading' }, this.schoolName, this.schoolSeed)),
       el(
         'div',
         { class: 'clockbar' },
@@ -188,6 +190,7 @@ export class GameScreen {
     }
 
     this.paintSkip();
+    this.paintSeed();
     this.people.setLocate((id) => this.placeOf(id));
     this.management.setLocate((id) => this.placeOf(id));
   }
@@ -195,7 +198,9 @@ export class GameScreen {
   /** Called when the screen opens, before the first clock frame and snapshot arrive. */
   show(school: School): void {
     this.schoolId = school.id;
+    this.peopleSeed = school.seed;
     this.schoolName.textContent = school.name;
+    this.paintSeed();
     this.nodes = [];
     this.presence = null;
     this.directory = new Map();
@@ -381,6 +386,10 @@ export class GameScreen {
       : '';
   }
 
+  private paintSeed(): void {
+    this.schoolSeed.textContent = this.peopleSeed === null ? '' : t('schoolSeed', { seed: this.peopleSeed });
+  }
+
   private paintTreeLabels(): void {
     for (const [id, button] of this.treeButtons) {
       const node = this.nodes.find((candidate) => candidate.id === id);

src/HSchool.Server/Api/SchoolEndpoints.cs

@@ -55,6 +55,7 @@ internal static class SchoolEndpoints
                 request.Map,
                 request.NameSetId,
                 request.NativeLanguage,
+                request.Seed,
                 NewCompletion<SchoolCreationOutcome>());
             commands.Enqueue(command);
 
@@ -508,7 +509,8 @@ internal sealed record CreateSchoolRequest(
     IReadOnlyList<string>? ModIds,
     MapLayout? Map,
     string? NameSetId,
-    string? NativeLanguage);
+    string? NativeLanguage,
+    int? Seed);
 
 internal sealed record SchoolResponse(
     int Id,
@@ -516,10 +518,11 @@ internal sealed record SchoolResponse(
     DateTime GameTime,
     bool Running,
     byte SpeedIndex,
-    IReadOnlyList<string> ModIds)
+    IReadOnlyList<string> ModIds,
+    int Seed)
 {
     public static SchoolResponse From(SchoolState school) =>
-        new(school.Id, school.Name, school.GameTime, school.Running, school.SpeedIndex, school.ModIds);
+        new(school.Id, school.Name, school.GameTime, school.Running, school.SpeedIndex, school.ModIds, school.Seed);
 }
 
 /// <summary>Everything the main menu needs in one request.</summary>

src/HSchool.Server/Game/GameCommand.cs

@@ -18,6 +18,7 @@ internal abstract record GameCommand
         MapLayout? Map,
         string? NameSetId,
         string? NativeLanguage,
+        int? Seed,
         TaskCompletionSource<SchoolCreationOutcome> Result) : GameCommand;
 
     internal sealed record DeleteSchool(int SchoolId, TaskCompletionSource<bool> Result) : GameCommand;

src/HSchool.Server/Game/GameLoopService.cs

@@ -378,9 +378,10 @@ internal sealed class GameLoopService(
 
             var id = _nextId++;
             store.WriteNextId(_nextId);
-            var nativeLanguage = NativeLanguages.Pick(names, id, command.NativeLanguage, rollIfOmitted: true);
+            var seed = command.Seed ?? Random.Shared.Next();
+            var nativeLanguage = NativeLanguages.Pick(names, seed, command.NativeLanguage, rollIfOmitted: true);
 
-            var worker = SpawnWorker(id, normalized, command.StartDate, running: true, ClockSpeed.DefaultIndex, isNew: true, packIds, command.Map, nameSetId, nativeLanguage);
+            var worker = SpawnWorker(id, normalized, command.StartDate, running: true, ClockSpeed.DefaultIndex, isNew: true, packIds, command.Map, nameSetId, nativeLanguage, seed);
             Track(worker);
             worker.Start();
 
@@ -402,7 +403,7 @@ internal sealed class GameLoopService(
                 throw;
             }
 
-            logger.LogInformation("School {SchoolId} \"{Name}\" created.", id, normalized);
+            logger.LogInformation("School {SchoolId} \"{Name}\" created with seed {Seed}.", id, normalized, seed);
             command.Result.TrySetResult(new SchoolCreationOutcome(worker.Snapshot, SchoolCreationError.None));
         }
         catch (Exception ex)
@@ -549,6 +550,7 @@ internal sealed class GameLoopService(
                 save.Map,
                 save.NameSetId,
                 save.NativeLanguage,
+                createSeed: null,
                 save.Presence);
             worker.Start();
 
@@ -598,6 +600,7 @@ internal sealed class GameLoopService(
         MapLayout? map,
         string? nameSetId,
         string? nativeLanguage,
+        int? createSeed = null,
         IReadOnlyList<PresenceSnapshot>? presence = null) =>
         new(
             id,
@@ -610,6 +613,7 @@ internal sealed class GameLoopService(
             map,
             nameSetId,
             nativeLanguage,
+            createSeed,
             presence,
             _options,
             clients,

src/HSchool.Server/Game/SchoolState.cs

@@ -10,7 +10,8 @@ internal sealed record SchoolState(
     DateTime GameTime,
     bool Running,
     byte SpeedIndex,
-    IReadOnlyList<string> ModIds);
+    IReadOnlyList<string> ModIds,
+    int Seed);
 
 /// <summary>Everything the main menu needs in one read.</summary>
 internal sealed record SchoolsState(int MaxSchools, IReadOnlyList<SchoolState> Schools);

src/HSchool.Server/Game/SchoolWorker.cs

@@ -34,6 +34,7 @@ internal sealed class SchoolWorker
     private readonly MapLayout? _savedMap;
     private readonly string? _nameSetId;
     private string? _nativeLanguage;
+    private readonly int? _createSeed;
     private readonly IReadOnlyList<PresenceSnapshot>? _savedPresence;
     private readonly Action<int> _onFailed;
 
@@ -67,6 +68,7 @@ internal sealed class SchoolWorker
         MapLayout? savedMap,
         string? nameSetId,
         string? nativeLanguage,
+        int? createSeed,
         IReadOnlyList<PresenceSnapshot>? savedPresence,
         SimulationOptions options,
         ClientRegistry clients,
@@ -86,6 +88,7 @@ internal sealed class SchoolWorker
         _savedMap = savedMap;
         _nameSetId = nameSetId;
         _nativeLanguage = nativeLanguage;
+        _createSeed = createSeed;
         _savedPresence = savedPresence;
         _options = options;
         _clients = clients;
@@ -94,7 +97,7 @@ internal sealed class SchoolWorker
         _mods = mods;
         _onFailed = onFailed;
         _logger = logger;
-        _snapshot = new SchoolState(id, name, time, running, (byte)speedIndex, modIds ?? []);
+        _snapshot = new SchoolState(id, name, time, running, (byte)speedIndex, modIds ?? [], createSeed ?? 0);
     }
 
     public int Id => _id;
@@ -589,7 +592,8 @@ internal sealed class SchoolWorker
                 school.Clock.Time,
                 school.Clock.IsRunning,
                 (byte)school.Clock.SpeedIndex,
-                school.Catalog?.PackIds ?? _modIds ?? []));
+                school.Catalog?.PackIds ?? _modIds ?? [],
+                school.PeopleSeed));
         Volatile.Write(ref _rosterSnapshot, school.Roster);
         Volatile.Write(ref _applicantSnapshot, school.Applicants);
         Volatile.Write(ref _timetableSnapshot, school.Timetable);
@@ -868,7 +872,12 @@ internal sealed class SchoolWorker
 
         if (_isNew)
         {
-            seed = school.Id;
+            if (_createSeed is not int createSeed)
+            {
+                throw new InvalidOperationException($"School {_id} was created without a people seed.");
+            }
+
+            seed = createSeed;
             native = ResolveNative(catalog, nameSetId, seed, _nativeLanguage, generating: true);
             _nativeLanguage = native;
             roster = RosterGenerator.Generate(catalog, map, seed, nameSetId, school.Clock.Time, native);

tests/HSchool.AppHost.Tests/GoldenSaveTests.cs

@@ -16,6 +16,7 @@ public class GoldenSaveTests(AppHostFixture fixture)
         var state = await SchoolApiTests.GetSchoolsAsync(client);
         var school = Assert.Single(state.Schools);
         Assert.Equal(1, school.Id);
+        Assert.Equal(1, school.Seed);
         Assert.Equal("Золотая", school.Name);
         Assert.Equal(new DateTime(2012, 3, 31, 6, 0, 0, DateTimeKind.Utc), school.GameTime);
         Assert.False(school.Running);
@@ -34,6 +35,8 @@ public class GoldenSaveTests(AppHostFixture fixture)
 
         var state = await SchoolApiTests.GetSchoolsAsync(client);
         var school = Assert.Single(state.Schools);
+        Assert.Equal(1, school.Id);
+        Assert.Equal(1, school.Seed);
         Assert.Equal("Золотая", school.Name);
 
         var people = await PeopleAsync(client, school.Id);

tests/HSchool.AppHost.Tests/PeopleApiTests.cs

@@ -139,14 +139,14 @@ public class PeopleApiTests(AppHostFixture fixture)
     {
         using var client = fixture.App.CreateHttpClient("server");
         await SchoolApiTests.ResetAsync(client);
-        var school = await SchoolApiTests.CreateAsync(client, "Люди семья", Start);
+        var school = await SchoolApiTests.CreateAsync(client, "Люди семья", Start, seed: 1);
 
         var page = await GetPeopleAsync(client, school.Id, "role=student&year=5&pageSize=10");
 
-        // Every fifth-to-tenth family is single-parent on purpose (design/people.md), and the
-        // roster seed is the school id — which depends on how many schools ran before this test.
-        // Demanding two parents from whoever happens to sort first therefore fails on some runs;
-        // look for a pupil who has a mother instead of assuming the first one does.
+        // Every fifth-to-tenth family is single-parent on purpose (design/people.md). The roster
+        // seed is no longer the school id, but a given page still mixes complete and single-parent
+        // houses, so demanding two parents from whoever sorts first fails on some seeds. Look for
+        // a pupil who has a mother instead of assuming the first one does.
         PersonCardResponse? card = null;
         foreach (var candidate in page.People)
         {

tests/HSchool.AppHost.Tests/SchoolApiTests.cs

@@ -491,9 +491,13 @@ public class SchoolApiTests(AppHostFixture fixture)
         return state;
     }
 
-    internal static async Task<SchoolResponse> CreateAsync(HttpClient client, string name, DateTime startDate)
+    internal static async Task<SchoolResponse> CreateAsync(
+        HttpClient client,
+        string name,
+        DateTime startDate,
+        int? seed = null)
     {
-        using var response = await PostAsync(client, name, startDate);
+        using var response = await PostAsync(client, name, startDate, seed);
         response.EnsureSuccessStatusCode();
 
         var created = await response.Content.ReadFromJsonAsync<SchoolResponse>(TestContext.Current.CancellationToken);
@@ -526,10 +530,14 @@ public class SchoolApiTests(AppHostFixture fixture)
         links = new[] { new { a = "yard", b = "office" } },
     };
 
-    private static Task<HttpResponseMessage> PostAsync(HttpClient client, string name, DateTime startDate) =>
+    private static Task<HttpResponseMessage> PostAsync(
+        HttpClient client,
+        string name,
+        DateTime startDate,
+        int? seed = null) =>
         client.PostAsJsonAsync(
             "/api/schools",
-            new { name, startDate },
+            seed is null ? (object)new { name, startDate } : new { name, startDate, seed },
             TestContext.Current.CancellationToken);
 
     private static async Task<string?> ProblemCodeAsync(HttpResponseMessage response)
@@ -544,6 +552,7 @@ public class SchoolApiTests(AppHostFixture fixture)
         DateTime GameTime,
         bool Running,
         byte SpeedIndex,
+        int Seed,
         IReadOnlyList<string>? ModIds = null);
 
     internal sealed record SchoolsResponse(

tests/HSchool.AppHost.Tests/SchoolSeedTests.cs

@@ -0,0 +1,90 @@
+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);
+}