Add MrGameEng.Net: WebSocket transport + delta component replication

Browsers can't speak UDP, so WebSocket is the engine's one transport.
The server side is a dependency-free RFC 6455 implementation over
TcpListener (handshake, frame codec with masking and fragmentation,
ping/pong — unit-tested against the RFC example vectors); the client
wraps ClientWebSocket, which works on desktop and maps to the browser
WebSocket in Blazor WASM. Both sit behind the poll-based INetConnection
so simulation systems drain messages from their own thread; client
sends are chained fire-and-forget (no blocking — wasm-safe).

Replication is server-authoritative: games register unmanaged component
types in a ReplicationSchema (same order both sides, up to 32 types),
ReplicationServer snapshots entities carrying NetId once per send and
ships each connection only the components that changed since its last
snapshot — a reliable ordered transport needs no acks for deltas. New
connections receive the full state through the same path; despawns are
tracked by set difference. ReplicationClient applies snapshots to a
local EntityStore and raises EntitySpawned so the game can decorate
replicated entities with presentation components.

Covered by 16 tests including a real loopback exchange between
WebSocketClient and WebSocketServer.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CLAUDE.md

@@ -27,19 +27,26 @@ is the living showcase — new engine features are demonstrated there.
 
 Engine libraries (each feature is a namespaced subfolder of its host):
 
-- **`Core`** — game loop, ECS world, scenes, time (`GameClock` with `TimeScale`; `GameSpeed`
-  for discrete pause/1×/3×/6× speed control over the clock, `context.UseGameSpeed(...)`;
-  `Calendar` turning scaled time into in-game days, `context.UseCalendar(secondsPerDay)`;
-  `Climate` — continuous seasonal/daily temperature and season over the calendar,
-  `context.UseClimate(settings)`),
-  plus **Input** (`MrGameEng.Input`: `InputManager`, `ActionMap`, `InputSystem`, in
-  `Core/Input/`). Depends only on MonoGame and Friflo.Engine.ECS.
+- **`Core`** — the platform-free kernel: ECS world, scenes and transition timing, time
+  (`GameClock` with `TimeScale`; `GameSpeed` for discrete pause/1×/3×/6× speed control over
+  the clock, `context.UseGameSpeed(...)`; `Calendar` turning scaled time into in-game days,
+  `context.UseCalendar(secondsPerDay)`; `Climate` — continuous seasonal/daily temperature
+  and season over the calendar, `context.UseClimate(settings)`), services, logging, and
+  **`HeadlessHost`** — a fixed-timestep loop without a window or GPU (dedicated servers,
+  batch simulation, tests). Depends only on Friflo.Engine.ECS — no MonoGame, no platform.
+- **`Host`** — the windowed MonoGame host: `GameHost` (wraps `Game`, owns the window and
+  `GraphicsDeviceManager`, publishes `GraphicsDevice` as a service), visual scene
+  transitions (`OverlayTransition`, `Transitions.Fade/Wipe`, `TransitionRenderer`), plus
+  **Input** (`MrGameEng.Input`: `InputManager`, `ActionMap`, `InputSystem`, in
+  `Host/Input/`). Nothing depends on `Host` except the game itself. → `Core`.
 - **`Graphics`** — custom batched renderer, camera, sprites, plus **Tilemaps**
   (`MrGameEng.Tilemaps`: code-built tile grids rendered through the batcher,
   `scene.UseTilemaps()` after `UseRenderer2D()`, in `Graphics/Tilemaps/`) and **Lighting**
   (`MrGameEng.Lighting`, `Graphics/Lighting/`: day/night ambient over the `Calendar` driving
-  `Renderer2D.AmbientLight` on world layers, `scene.UseDayNight(renderer)`; a sampleable
-  `DayNight.SampleAt` for the simulation — point lights and shadows land here later). → `Core`.
+  `Renderer2D.AmbientLight` on world layers, `scene.UseDayNight(renderer)`; plus a per-cell
+  **lightmap** — `LightmapBuilder` (ambient × occlusion + point lights with grid-traced shadows),
+  `PointLight` component, multiplied over the world via `scene.UseLighting(...)`, sampleable with
+  `Lighting.SampleAt` for the simulation). → `Core`.
 - **`Audio`** — ogg playback (NVorbis); `AudioManager` with `SoundVolume`/`MasterVolume`
   (one knob for effects + music). → `Core`.
 - **`Content`** — the asset/content pipeline: **Assets** (`MrGameEng.Assets`: runtime
@@ -57,6 +64,13 @@ Engine libraries (each feature is a namespaced subfolder of its host):
   **Collisions** (`MrGameEng.Collisions`: `Collider` component, spatial hash rebuilt per
   tick, pairs/queries/raycast, `scene.UseCollisions()` after movement systems).
   → `Core`, `Graphics` (Collisions needs `Transform2D`, `RectF`).
+- **`Net`** — multiplayer building blocks, browser-compatible by design: a dependency-free
+  RFC 6455 WebSocket server over `TcpListener` (browsers can't speak UDP, so WebSocket is
+  the engine's one transport), a `ClientWebSocket`-based client (works in Blazor WASM),
+  both behind the poll-based `INetConnection`; server-authoritative component replication
+  (`ReplicationSchema` of unmanaged components, `ReplicationServer` sending per-connection
+  deltas — no acks needed over a reliable ordered transport, `ReplicationClient` applying
+  snapshots to a local store, `NetId`). → `Core`.
 - **`UI`** — Myra integration (`scene.UseUI()` after `UseRenderer2D()`),
   **DevConsole** (`MrGameEng.DevConsole`: in-game console capturing `Core.Log`,
   `scene.UseDevConsole()` last in OnLoad) and **Inspector** (`MrGameEng.Inspector`: a
@@ -68,9 +82,13 @@ Engine libraries (each feature is a namespaced subfolder of its host):
   netstandard2.0 analyzer.
 
 Dependency rule: a library may depend only on `Core` and `Graphics`; `Core` depends only
-on MonoGame and Friflo.Engine.ECS. Features grouped into one library share its package
-set (e.g. `Content` carries both FontStash and StbImage) — keep optional/heavy deps
-(Myra, NVorbis) in their own library so the rest of the engine stays free of them.
+on Friflo.Engine.ECS (no MonoGame — the simulation must run headless). MonoGame is pulled
+in by the platform/graphics libraries (`Host`, `Graphics`, `Audio`). Platform resources
+(e.g. `GraphicsDevice`) are published by hosts as services in `EngineContext.Services`;
+graphics code reaches the device via `context.GetGraphicsDevice()` (extension in
+`Graphics`). Features grouped into one library share its package set (e.g. `Content`
+carries both FontStash and StbImage) — keep optional/heavy deps (Myra, NVorbis) in their
+own library so the rest of the engine stays free of them.
 
 ## Commands
 

Directory.Build.props

@@ -1,5 +1,4 @@
 <Project>
-
   <PropertyGroup>
     <LangVersion>latest</LangVersion>
     <Nullable>enable</Nullable>
@@ -13,5 +12,4 @@
   <PropertyGroup Condition="$(MSBuildProjectName.StartsWith('MrGameEng.')) AND !$(MSBuildProjectName.EndsWith('.Tests')) AND !$(MSBuildProjectName.EndsWith('.Generator')) AND !$(MSBuildProjectName.EndsWith('.Sample'))">
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
   </PropertyGroup>
-
 </Project>

Directory.Packages.props

@@ -16,4 +16,4 @@
     <PackageVersion Include="xunit.v3" Version="3.2.2" />
     <PackageVersion Include="xunit.runner.visualstudio" Version="3.1.5" />
   </ItemGroup>
-</Project>
+</Project>

MrGameEng.sln

@@ -39,6 +39,14 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MrGameEng.UI.Tests", "tests
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MrGameEng.Audio.Tests", "tests\MrGameEng.Audio.Tests\MrGameEng.Audio.Tests.csproj", "{4407F6E6-0B65-41A3-ADFA-B78684A9B918}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MrGameEng.Host", "src\MrGameEng.Host\MrGameEng.Host.csproj", "{59818072-0D2B-4007-A50F-1343FA189EC6}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MrGameEng.Host.Tests", "tests\MrGameEng.Host.Tests\MrGameEng.Host.Tests.csproj", "{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MrGameEng.Net", "src\MrGameEng.Net\MrGameEng.Net.csproj", "{A4E754C7-C5FD-43A2-B345-34152D3A22D1}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MrGameEng.Net.Tests", "tests\MrGameEng.Net.Tests\MrGameEng.Net.Tests.csproj", "{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -229,6 +237,54 @@ Global
 		{4407F6E6-0B65-41A3-ADFA-B78684A9B918}.Release|x64.Build.0 = Release|Any CPU
 		{4407F6E6-0B65-41A3-ADFA-B78684A9B918}.Release|x86.ActiveCfg = Release|Any CPU
 		{4407F6E6-0B65-41A3-ADFA-B78684A9B918}.Release|x86.Build.0 = Release|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Debug|x64.Build.0 = Debug|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Debug|x86.Build.0 = Debug|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Release|Any CPU.Build.0 = Release|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Release|x64.ActiveCfg = Release|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Release|x64.Build.0 = Release|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Release|x86.ActiveCfg = Release|Any CPU
+		{59818072-0D2B-4007-A50F-1343FA189EC6}.Release|x86.Build.0 = Release|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Debug|x64.Build.0 = Debug|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Debug|x86.Build.0 = Debug|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Release|Any CPU.Build.0 = Release|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Release|x64.ActiveCfg = Release|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Release|x64.Build.0 = Release|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Release|x86.ActiveCfg = Release|Any CPU
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2}.Release|x86.Build.0 = Release|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Debug|x64.Build.0 = Debug|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Debug|x86.Build.0 = Debug|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Release|x64.ActiveCfg = Release|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Release|x64.Build.0 = Release|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Release|x86.ActiveCfg = Release|Any CPU
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1}.Release|x86.Build.0 = Release|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Debug|x64.Build.0 = Debug|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Debug|x86.Build.0 = Debug|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Release|Any CPU.Build.0 = Release|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Release|x64.ActiveCfg = Release|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Release|x64.Build.0 = Release|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Release|x86.ActiveCfg = Release|Any CPU
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -249,5 +305,9 @@ Global
 		{C34F2AFF-F2B0-4AC4-A6F9-B114A06FB272} = {0AB3BF05-4346-4AA6-1389-037BE0695223}
 		{7F7D9641-2409-40CB-88A9-56BCE8C90A45} = {0AB3BF05-4346-4AA6-1389-037BE0695223}
 		{4407F6E6-0B65-41A3-ADFA-B78684A9B918} = {0AB3BF05-4346-4AA6-1389-037BE0695223}
+		{59818072-0D2B-4007-A50F-1343FA189EC6} = {827E0CD3-B72D-47B6-A68D-7590B98EB39B}
+		{B3EB5318-5EC0-4F23-8ECA-0EC5A0C4DFD2} = {0AB3BF05-4346-4AA6-1389-037BE0695223}
+		{A4E754C7-C5FD-43A2-B345-34152D3A22D1} = {827E0CD3-B72D-47B6-A68D-7590B98EB39B}
+		{434C24AC-08C6-483E-A2DE-6DBC8A4DE791} = {0AB3BF05-4346-4AA6-1389-037BE0695223}
 	EndGlobalSection
 EndGlobal

docs/architecture.md

@@ -33,11 +33,13 @@
 
 | Библиотека (сборка)          | Фичи (неймспейсы) и ответственность                        |
 |------------------------------|------------------------------------------------------------|
-| `MrGameEng.Core`             | Игровой цикл (хост над `Game`), `EntityStore`, `SystemRoot`, сцены, время (`GameClock.TimeScale`; `GameSpeed` — дискретная скорость пауза/1×/3×/6× поверх часов; `Calendar` — игровые дни поверх масштабированного времени, `context.UseCalendar(...)`; `Climate` — непрерывная сезонная/суточная температура и сезон поверх календаря, `context.UseClimate(...)`), жизненный цикл. **Input** (`MrGameEng.Input`, `Core/Input/`): клавиатура, мышь, геймпад, action maps |
-| `MrGameEng.Graphics`         | Собственный батчер-рендерер (см. «Рендеринг»), камера, спрайты, анимации, слои. **Tilemaps** (`MrGameEng.Tilemaps`, `Graphics/Tilemaps/`): тайловые карты кодом — `TileGrid` + `TileSet` + компонент `Tilemap`, отрисовка видимых клеток через батчер. **Lighting** (`MrGameEng.Lighting`, `Graphics/Lighting/`): амбиент день/ночь поверх `Calendar` → `Renderer2D.AmbientLight` на World-слоях, `scene.UseDayNight(renderer)`, сэмплируемый `DayNight.SampleAt` для симуляции |
+| `MrGameEng.Core`             | Платформо-независимое ядро (зависит только от Friflo): `EngineContext`, `EntityStore`, `SystemRoot`, сцены и переходы (тайминг — `Transition`, `SceneManager`; визуал переходов — в `Host`), время (`GameClock.TimeScale`; `GameSpeed` — дискретная скорость пауза/1×/3×/6× поверх часов; `Calendar` — игровые дни поверх масштабированного времени, `context.UseCalendar(...)`; `Climate` — непрерывная сезонная/суточная температура и сезон поверх календаря, `context.UseClimate(...)`), жизненный цикл, `ServiceRegistry`, `Log`. **`HeadlessHost`** — цикл без окна и GPU на фиксированном тике (`Tick`/`RunTicks`/`Run` с realtime-пейсингом): дедикейтед-серверы, батч-симуляция, тесты |
+| `MrGameEng.Host`             | Оконный MonoGame-хост: `GameHost` (обёртка над `Game` — цикл, окно, `GraphicsDeviceManager`; публикует `GraphicsDevice` сервисом в контексте), визуальные переходы сцен (`OverlayTransition`, фабрики `Transitions.Fade/Wipe`, `TransitionRenderer`). **Input** (`MrGameEng.Input`, `Host/Input/`): клавиатура, мышь, геймпад, action maps |
+| `MrGameEng.Graphics`         | Собственный батчер-рендерер (см. «Рендеринг»), камера, спрайты, анимации, слои. **Tilemaps** (`MrGameEng.Tilemaps`, `Graphics/Tilemaps/`): тайловые карты кодом — `TileGrid` + `TileSet` + компонент `Tilemap`, отрисовка видимых клеток через батчер. **Lighting** (`MrGameEng.Lighting`, `Graphics/Lighting/`): амбиент день/ночь поверх `Calendar` → `Renderer2D.AmbientLight`, `scene.UseDayNight(renderer)`; по-клеточный лайтмап — `LightmapBuilder` (амбиент × окклюзия + точечные `PointLight` с трассировкой теней), накладывается multiply поверх мира через `scene.UseLighting(...)`, сэмплируется `Lighting.SampleAt` |
 | `MrGameEng.Audio`            | Звуковые эффекты и музыка (NVorbis); `AudioManager` с `SoundVolume`/`MasterVolume` (одна ручка на эффекты и музыку) |
 | `MrGameEng.Content`          | Пайплайн контента. **Assets** (`MrGameEng.Assets`): runtime-загрузка без Content Pipeline, кэш, `AssetRef<T>`. **Atlases** (`MrGameEng.Atlases`): текстурные атласы — сборка из дерева картинок (`AtlasBuilder`) и рантайм-загрузка (`TextureAtlas`), CLI `tools/MrGameEng.AtlasTool`. **Mods** (`MrGameEng.Mods`): система модов — порядок загрузки, JSON-дефы, локализация, слияние деревьев контента |
 | `MrGameEng.Simulation`       | Детерминированные геймплей-примитивы без данных мира. **Pathfinding** (`MrGameEng.Pathfinding`): A*, Dijkstra, BFS, flow fields по гриду. **AI** (`MrGameEng.AI`): utility-ИИ — кривые отклика, соображения, действия, выбор (`UtilityAi<TContext>`), `Blackboard`. **Collisions** (`MrGameEng.Collisions`): компонент `Collider`, spatial hash, пары/запросы/raycast |
+| `MrGameEng.Net`              | Мультиплеер, совместимый с браузером по построению: WebSocket-сервер (RFC 6455 поверх `TcpListener`, без зависимостей — браузер не умеет UDP, поэтому транспорт движка один — WebSocket), клиент на `ClientWebSocket` (работает в Blazor WASM), оба за poll-интерфейсом `INetConnection`; server-authoritative репликация компонентов: `ReplicationSchema` (unmanaged-компоненты, до 32 типов), `ReplicationServer` (пер-соединенческие дельты против последнего отправленного — ack не нужны поверх надёжного упорядоченного транспорта), `ReplicationClient` (применение снапшотов в локальный `EntityStore`), компонент `NetId` |
 | `MrGameEng.UI`               | Игровой UI на [Myra](https://github.com/rds1983/Myra): `Desktop` на сцену, виджеты, скининг. **DevConsole** (`MrGameEng.DevConsole`): ингейм-консоль — логи `Log`, команды, история, автодополнение. **Inspector** (`MrGameEng.Inspector`): ECS-дебагер в духе Chrome DevTools — дерево сущностей по архетипам, компоненты/поля с правкой простых полей, выбор кликом по миру с подсветкой, вкладка перфа рендера (`scene.UseInspector(renderer)`, F1) |
 | `MrGameEng.Assets.Generator` | Roslyn incremental source generator: классы с типизированными хендлами ресурсов (отдельный анализатор netstandard2.0) |
 
@@ -69,19 +71,28 @@
 ### Правило зависимостей
 
 ```
-MrGameEng.Audio       ─┐
-MrGameEng.Graphics    ─┼──► MrGameEng.Core ──► MonoGame.Framework.DesktopGL
-                       │                   └──► Friflo.Engine.ECS
+MrGameEng.Host        ─┐
+MrGameEng.Audio       ─┤
+MrGameEng.Net         ─┤
+MrGameEng.Graphics    ─┼──► MrGameEng.Core ──► Friflo.Engine.ECS
+                       │
 MrGameEng.Content     ─┤
 MrGameEng.Simulation  ─┤                         (Content — за Texture2DRegion,
 MrGameEng.UI          ─┴──► MrGameEng.Graphics    Simulation/UI — за Transform2D/рендер)
 ```
 
-Библиотека зависит **только от `Core` и `Graphics`**. `Core` зависит только от MonoGame
-и Friflo. Если двум библиотекам нужен общий тип — он переезжает в `Core` (или, если это
-графический тип, в `Graphics`). `Content` тянет `Graphics` (атласы выдают
-`Texture2DRegion`); `Simulation` тянет `Graphics` (`Collisions` использует `Transform2D`,
-`RectF`); `UI` — только `Core` (Myra рисует своим SpriteBatch).
+Библиотека зависит **только от `Core` и `Graphics`**. `Core` зависит только от Friflo —
+ни MonoGame, ни другой платформы: благодаря этому симуляция запускается и без окна
+(`HeadlessHost`). MonoGame (`MonoGame.Framework.DesktopGL`) тянут платформенные и
+графические библиотеки: `Host`, `Graphics`, `Audio` (и транзитивно их потребители).
+Платформенные ресурсы (например `GraphicsDevice`) хосты публикуют сервисами в
+`EngineContext.Services`; графический код достаёт девайс через
+`context.GetGraphicsDevice()` (расширение в `Graphics`). На `Host` не зависит никто,
+кроме самой игры — это точка входа оконной платформы. Если двум библиотекам нужен общий
+тип — он переезжает в `Core` (или, если это графический тип, в `Graphics`). `Content`
+тянет `Graphics` (атласы выдают `Texture2DRegion`); `Simulation` тянет `Graphics`
+(`Collisions` использует `Transform2D`, `RectF`); `UI` — только `Core` (Myra рисует
+своим SpriteBatch).
 
 Фичи, собранные в одну библиотеку, делят её набор пакетов (например, `Content` несёт и
 FontStash, и StbImage). Тяжёлые/опциональные зависимости (Myra, NVorbis) держим в
@@ -345,12 +356,15 @@ CLI-обёртка: `dotnet run --project tools/MrGameEng.AtlasTool -- <исто
 
 - `SceneManager` владеет активной сценой; обычное переключение откладывается до начала
   следующего кадра (сцена никогда не выгружается посреди собственного кадра).
-- `Scenes.Switch(scene, Transition.Fade(0.5f))` — переключение с визуальным переходом:
+- `Scenes.Switch(scene, Transitions.Fade(0.5f))` — переключение с визуальным переходом:
   фаза закрытия (старая сцена живёт) → своп при полном покрытии → фаза открытия.
   Тяжёлый `OnLoad` новой сцены скрыт за полностью закрытым экраном.
-- Встроенные переходы: `Transition.Fade(duration, color)` и `Transition.Wipe(duration, color)`
-  (шторка). Свои — наследованием от `Transition` (рисование через `TransitionRenderer.Fill`
-  в нормализованных координатах экрана).
+- Тайминг-машина (`Transition` — длительности фаз, покрытие) живёт в `Core` и работает
+  и в headless-контексте; визуал — в `Host`: встроенные `Transitions.Fade(duration, color)`
+  и `Transitions.Wipe(duration, color)` (шторка). Свои — наследованием от
+  `OverlayTransition` (рисование через `TransitionRenderer.Fill` в нормализованных
+  координатах экрана); `GameHost` рисует оверлей поверх сцены, читая
+  `Scenes.ActiveTransition`/`TransitionCoverage`/`TransitionPhase`.
 - Переходы идут по **unscaled**-времени: работают при паузе геймплея (`TimeScale = 0`).
 - Повторный `Switch` во время перехода заменяет целевую сцену, не перезапуская переход.
 

src/MrGameEng.Audio/MrGameEng.Audio.csproj

@@ -1,13 +1,14 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <PackageReference Include="NVorbis" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
-  </ItemGroup>
-</Project>
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MonoGame.Framework.DesktopGL" />
+    <PackageReference Include="NVorbis" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
+  </ItemGroup>
+</Project>

src/MrGameEng.Content/Assets/AssetManager.cs

@@ -2,6 +2,7 @@ using FontStashSharp;
 using Microsoft.Xna.Framework.Audio;
 using Microsoft.Xna.Framework.Graphics;
 using MrGameEng.Core;
+using MrGameEng.Graphics;
 
 namespace MrGameEng.Assets;
 
@@ -103,7 +104,7 @@ public sealed class AssetManager : IDisposable
     {
         using var stream = File.OpenRead(path);
         return Texture2D.FromStream(
-            context.GraphicsDevice,
+            context.GetGraphicsDevice(),
             stream,
             DefaultColorProcessors.PremultiplyAlpha
         );
@@ -123,7 +124,7 @@ public sealed class AssetManager : IDisposable
     }
 
     private static Effect LoadEffect(EngineContext context, string path) =>
-        new(context.GraphicsDevice, File.ReadAllBytes(path));
+        new(context.GetGraphicsDevice(), File.ReadAllBytes(path));
 }
 
 /// <summary>Wires the assets module into the engine.</summary>

src/MrGameEng.Content/Atlases/AtlasesEngineExtensions.cs

@@ -1,5 +1,6 @@
 using MrGameEng.Assets;
 using MrGameEng.Core;
+using MrGameEng.Graphics;
 
 namespace MrGameEng.Atlases;
 
@@ -14,6 +15,6 @@ public static class AtlasesEngineExtensions
     public static void UseTextureAtlases(this EngineContext context)
     {
         var assets = context.Services.Get<AssetManager>();
-        assets.RegisterLoader((_, path) => TextureAtlas.Load(context.GraphicsDevice, path));
+        assets.RegisterLoader((_, path) => TextureAtlas.Load(context.GetGraphicsDevice(), path));
     }
 }

src/MrGameEng.Core/EngineContext.cs

@@ -1,10 +1,11 @@
-using Microsoft.Xna.Framework.Graphics;
-
 namespace MrGameEng.Core;
 
 /// <summary>
-/// Root object handed to scenes and systems: time, scene manager, services and graphics device.
-/// Created by <see cref="GameHost"/>; can also be created standalone for headless tests.
+/// Root object handed to scenes and systems: time, scene manager and services.
+/// Created by a host (the MonoGame game host or <see cref="HeadlessHost"/>); can also be
+/// created standalone for unit tests. Platform resources such as the graphics device are
+/// published through <see cref="Services"/> by hosts that have them — the core itself has
+/// no platform dependencies.
 /// </summary>
 public sealed class EngineContext
 {
@@ -17,38 +18,16 @@ public sealed class EngineContext
     /// <summary>Registry of module services (input, audio, assets, …).</summary>
     public ServiceRegistry Services { get; } = new();
 
-    /// <summary>
-    /// The graphics device. Available once the host is initialized;
-    /// throws when accessed in a headless context (unit tests).
-    /// </summary>
-    public GraphicsDevice GraphicsDevice =>
-        _graphicsDevice
-        ?? throw new InvalidOperationException(
-            "GraphicsDevice is not available (headless context)."
-        );
-
-    /// <summary>True when a graphics device is attached.</summary>
-    public bool HasGraphicsDevice => _graphicsDevice is not null;
-
-    private GraphicsDevice? _graphicsDevice;
-
-    /// <summary>Creates a context. Games normally never create one themselves — <see cref="GameHost"/> does.</summary>
+    /// <summary>Creates a context. Games normally never create one themselves — the host does.</summary>
     public EngineContext()
     {
         Scenes = new SceneManager(this);
     }
 
-    internal void AttachGraphicsDevice(GraphicsDevice device) => _graphicsDevice = device;
-
     /// <summary>
-    /// Disposes everything the context owns: registered <see cref="IDisposable"/> services
-    /// and the transition renderer. <paramref name="except"/> (the host itself, also a
-    /// registered service) is skipped — it is being disposed by the caller already.
-    /// Called by <see cref="GameHost.Dispose(bool)"/>.
+    /// Disposes everything the context owns: registered <see cref="IDisposable"/> services.
+    /// Instances in <paramref name="except"/> (the host itself, platform resources the host
+    /// disposes on its own) are skipped. Called by hosts on shutdown.
     /// </summary>
-    internal void DisposeOwnedResources(object except)
-    {
-        Scenes.DisposeRenderer();
-        Services.DisposeServices(except);
-    }
+    internal void DisposeOwnedResources(params object[] except) => Services.DisposeServices(except);
 }

src/MrGameEng.Core/Formulas/Formula.cs

@@ -0,0 +1,60 @@
+namespace MrGameEng.Formulas;
+
+/// <summary>
+/// A compiled arithmetic expression — the keystone of the data-driven gene system. A formula is
+/// parsed once from a string in a def (e.g. a gene effect on a trait) into a delegate tree, then
+/// evaluated many times against an <see cref="IFormulaContext"/> that supplies variable values
+/// (gene values, environment readings, other traits). Evaluation is deterministic and
+/// allocation-free; all the work happens in <see cref="Compile"/>.
+///
+/// <para>Grammar: numbers, variables, the constants <c>pi</c>/<c>tau</c>/<c>e</c>, operators
+/// <c>+ - * / %</c>, comparisons <c>&lt; &gt; &lt;= &gt;= == !=</c>, logical <c>&amp;&amp; || !</c>,
+/// the ternary <c>cond ? a : b</c>, and functions <c>abs sign floor ceil round sqrt exp log sin cos
+/// tan min max pow clamp lerp step</c>. Comparisons and logical operators yield <c>1</c>/<c>0</c>.</para>
+/// </summary>
+public sealed class Formula
+{
+    private static readonly IFormulaContext Empty = new EmptyContext();
+
+    private readonly Func<IFormulaContext, float> _root;
+
+    private Formula(string source, Func<IFormulaContext, float> root)
+    {
+        Source = source;
+        _root = root;
+    }
+
+    /// <summary>The original expression text this formula was compiled from.</summary>
+    public string Source { get; }
+
+    /// <summary>
+    /// Parses and compiles <paramref name="expression"/>. Throws <see cref="FormulaException"/> on any
+    /// lexical or syntactic error, with the offending position.
+    /// </summary>
+    public static Formula Compile(string expression)
+    {
+        ArgumentNullException.ThrowIfNull(expression);
+        var tokens = FormulaLexer.Tokenize(expression);
+        var root = new FormulaParser(tokens).ParseProgram();
+        return new Formula(expression, root);
+    }
+
+    /// <summary>Evaluates the formula, resolving variables through <paramref name="context"/>.</summary>
+    public float Evaluate(IFormulaContext context)
+    {
+        ArgumentNullException.ThrowIfNull(context);
+        return _root(context);
+    }
+
+    /// <summary>
+    /// Evaluates a formula that references no variables. Throws <see cref="FormulaException"/> if it
+    /// turns out to reference one.
+    /// </summary>
+    public float Evaluate() => _root(Empty);
+
+    private sealed class EmptyContext : IFormulaContext
+    {
+        public float Resolve(string name) =>
+            throw new FormulaException($"No context to resolve variable '{name}'.");
+    }
+}

src/MrGameEng.Core/Formulas/FormulaContext.cs

@@ -0,0 +1,28 @@
+namespace MrGameEng.Formulas;
+
+/// <summary>
+/// Supplies variable values to a compiled <see cref="Formula"/>. A context maps a variable name
+/// (a gene value, an environment reading, another trait…) to a number; the formula engine itself
+/// is data-agnostic, so any consumer can back this with whatever lookup it owns.
+/// </summary>
+public interface IFormulaContext
+{
+    /// <summary>
+    /// Returns the value bound to <paramref name="name"/>. Throw (e.g. <see cref="FormulaException"/>)
+    /// if the name is unknown — the engine does not invent a default.
+    /// </summary>
+    float Resolve(string name);
+}
+
+/// <summary>An <see cref="IFormulaContext"/> backed by a lookup delegate — handy for tests and ad-hoc use.</summary>
+public sealed class DelegateFormulaContext : IFormulaContext
+{
+    private readonly Func<string, float> _resolve;
+
+    /// <summary>Wraps <paramref name="resolve"/>; it is called once per variable reference per evaluation.</summary>
+    public DelegateFormulaContext(Func<string, float> resolve) =>
+        _resolve = resolve ?? throw new ArgumentNullException(nameof(resolve));
+
+    /// <inheritdoc />
+    public float Resolve(string name) => _resolve(name);
+}

src/MrGameEng.Core/Formulas/FormulaException.cs

@@ -0,0 +1,12 @@
+namespace MrGameEng.Formulas;
+
+/// <summary>
+/// Thrown when a <see cref="Formula"/> cannot be lexed or parsed, or when a compiled formula
+/// references a variable the context cannot resolve at evaluation time.
+/// </summary>
+public sealed class FormulaException : Exception
+{
+    /// <summary>Creates the exception with a human-readable <paramref name="message"/>.</summary>
+    public FormulaException(string message)
+        : base(message) { }
+}

src/MrGameEng.Core/Formulas/FormulaFunctions.cs

@@ -0,0 +1,90 @@
+using Node = System.Func<MrGameEng.Formulas.IFormulaContext, float>;
+
+namespace MrGameEng.Formulas;
+
+/// <summary>
+/// The built-in function set available inside formulas. Each entry validates its argument count at
+/// compile time and returns a <see cref="Node"/> that evaluates its operands then the math. Kept
+/// deterministic and side-effect-free so formulas stay pure.
+/// </summary>
+internal static class FormulaFunctions
+{
+    public static Node Build(string name, List<Node> args)
+    {
+        switch (name)
+        {
+            case "abs":
+                return Unary(name, args, MathF.Abs);
+            case "sign":
+                return Unary(name, args, x => MathF.Sign(x));
+            case "floor":
+                return Unary(name, args, MathF.Floor);
+            case "ceil":
+                return Unary(name, args, MathF.Ceiling);
+            case "round":
+                return Unary(name, args, MathF.Round);
+            case "sqrt":
+                return Unary(name, args, MathF.Sqrt);
+            case "exp":
+                return Unary(name, args, MathF.Exp);
+            case "log":
+                return args.Count == 2
+                    ? Binary(name, args, MathF.Log)
+                    : Unary(name, args, MathF.Log);
+            case "sin":
+                return Unary(name, args, MathF.Sin);
+            case "cos":
+                return Unary(name, args, MathF.Cos);
+            case "tan":
+                return Unary(name, args, MathF.Tan);
+            case "min":
+                return Binary(name, args, MathF.Min);
+            case "max":
+                return Binary(name, args, MathF.Max);
+            case "pow":
+                return Binary(name, args, MathF.Pow);
+            case "clamp":
+                return Ternary(name, args, (x, lo, hi) => Math.Clamp(x, lo, hi));
+            case "lerp":
+                return Ternary(name, args, (a, b, t) => a + (b - a) * t);
+            case "step":
+                return Binary(name, args, (edge, x) => x < edge ? 0f : 1f);
+            default:
+                throw new FormulaException($"Unknown function '{name}'.");
+        }
+    }
+
+    private static Node Unary(string name, List<Node> args, Func<float, float> op)
+    {
+        Require(name, args, 1);
+        var a = args[0];
+        return ctx => op(a(ctx));
+    }
+
+    private static Node Binary(string name, List<Node> args, Func<float, float, float> op)
+    {
+        Require(name, args, 2);
+        var a = args[0];
+        var b = args[1];
+        return ctx => op(a(ctx), b(ctx));
+    }
+
+    private static Node Ternary(string name, List<Node> args, Func<float, float, float, float> op)
+    {
+        Require(name, args, 3);
+        var a = args[0];
+        var b = args[1];
+        var c = args[2];
+        return ctx => op(a(ctx), b(ctx), c(ctx));
+    }
+
+    private static void Require(string name, List<Node> args, int count)
+    {
+        if (args.Count != count)
+        {
+            throw new FormulaException(
+                $"Function '{name}' expects {count} argument(s) but got {args.Count}."
+            );
+        }
+    }
+}

src/MrGameEng.Core/Formulas/FormulaLexer.cs

@@ -0,0 +1,217 @@
+using System.Globalization;
+
+namespace MrGameEng.Formulas;
+
+internal enum TokenType
+{
+    Number,
+    Identifier,
+    Plus,
+    Minus,
+    Star,
+    Slash,
+    Percent,
+    LParen,
+    RParen,
+    Comma,
+    Less,
+    Greater,
+    LessEqual,
+    GreaterEqual,
+    EqualEqual,
+    NotEqual,
+    And,
+    Or,
+    Not,
+    Question,
+    Colon,
+    End,
+}
+
+internal readonly struct Token(TokenType type, int position, float number = 0f, string text = "")
+{
+    public TokenType Type { get; } = type;
+    public int Position { get; } = position;
+    public float Number { get; } = number;
+    public string Text { get; } = text;
+}
+
+/// <summary>
+/// Turns a formula string into a flat token list. Pure and allocation-light; recognizes numbers,
+/// identifiers, the arithmetic/comparison/logical operators and the punctuation the parser needs.
+/// </summary>
+internal static class FormulaLexer
+{
+    public static List<Token> Tokenize(string source)
+    {
+        var tokens = new List<Token>();
+        var i = 0;
+        while (i < source.Length)
+        {
+            var c = source[i];
+            if (char.IsWhiteSpace(c))
+            {
+                i++;
+                continue;
+            }
+
+            if (
+                char.IsDigit(c)
+                || (c == '.' && i + 1 < source.Length && char.IsDigit(source[i + 1]))
+            )
+            {
+                var start = i;
+                while (i < source.Length && (char.IsDigit(source[i]) || source[i] == '.'))
+                {
+                    i++;
+                }
+
+                var span = source.AsSpan(start, i - start);
+                if (
+                    !float.TryParse(
+                        span,
+                        NumberStyles.Float,
+                        CultureInfo.InvariantCulture,
+                        out var value
+                    )
+                )
+                {
+                    throw new FormulaException(
+                        $"Invalid number '{span.ToString()}' at position {start}."
+                    );
+                }
+
+                tokens.Add(new Token(TokenType.Number, start, value));
+                continue;
+            }
+
+            if (char.IsLetter(c) || c == '_')
+            {
+                var start = i;
+                while (i < source.Length && (char.IsLetterOrDigit(source[i]) || source[i] == '_'))
+                {
+                    i++;
+                }
+
+                tokens.Add(
+                    new Token(TokenType.Identifier, start, text: source.Substring(start, i - start))
+                );
+                continue;
+            }
+
+            var pos = i;
+            switch (c)
+            {
+                case '+':
+                    tokens.Add(new Token(TokenType.Plus, pos));
+                    i++;
+                    break;
+                case '-':
+                    tokens.Add(new Token(TokenType.Minus, pos));
+                    i++;
+                    break;
+                case '*':
+                    tokens.Add(new Token(TokenType.Star, pos));
+                    i++;
+                    break;
+                case '/':
+                    tokens.Add(new Token(TokenType.Slash, pos));
+                    i++;
+                    break;
+                case '%':
+                    tokens.Add(new Token(TokenType.Percent, pos));
+                    i++;
+                    break;
+                case '(':
+                    tokens.Add(new Token(TokenType.LParen, pos));
+                    i++;
+                    break;
+                case ')':
+                    tokens.Add(new Token(TokenType.RParen, pos));
+                    i++;
+                    break;
+                case ',':
+                    tokens.Add(new Token(TokenType.Comma, pos));
+                    i++;
+                    break;
+                case '?':
+                    tokens.Add(new Token(TokenType.Question, pos));
+                    i++;
+                    break;
+                case ':':
+                    tokens.Add(new Token(TokenType.Colon, pos));
+                    i++;
+                    break;
+                case '<':
+                    i = AddMaybeEqual(tokens, source, i, TokenType.LessEqual, TokenType.Less);
+                    break;
+                case '>':
+                    i = AddMaybeEqual(tokens, source, i, TokenType.GreaterEqual, TokenType.Greater);
+                    break;
+                case '=':
+                    if (Next(source, i) == '=')
+                    {
+                        tokens.Add(new Token(TokenType.EqualEqual, pos));
+                        i += 2;
+                        break;
+                    }
+
+                    throw new FormulaException($"Expected '==' at position {pos}.");
+                case '!':
+                    if (Next(source, i) == '=')
+                    {
+                        tokens.Add(new Token(TokenType.NotEqual, pos));
+                        i += 2;
+                        break;
+                    }
+
+                    tokens.Add(new Token(TokenType.Not, pos));
+                    i++;
+                    break;
+                case '&':
+                    if (Next(source, i) == '&')
+                    {
+                        tokens.Add(new Token(TokenType.And, pos));
+                        i += 2;
+                        break;
+                    }
+
+                    throw new FormulaException($"Expected '&&' at position {pos}.");
+                case '|':
+                    if (Next(source, i) == '|')
+                    {
+                        tokens.Add(new Token(TokenType.Or, pos));
+                        i += 2;
+                        break;
+                    }
+
+                    throw new FormulaException($"Expected '||' at position {pos}.");
+                default:
+                    throw new FormulaException($"Unexpected character '{c}' at position {pos}.");
+            }
+        }
+
+        tokens.Add(new Token(TokenType.End, source.Length));
+        return tokens;
+    }
+
+    private static int AddMaybeEqual(
+        List<Token> tokens,
+        string source,
+        int i,
+        TokenType withEqual,
+        TokenType plain
+    )
+    {
+        if (Next(source, i) == '=')
+        {
+            tokens.Add(new Token(withEqual, i));
+            return i + 2;
+        }
+
+        tokens.Add(new Token(plain, i));
+        return i + 1;
+    }
+
+    private static char Next(string source, int i) => i + 1 < source.Length ? source[i + 1] : '\0';
+}

src/MrGameEng.Core/Formulas/FormulaParser.cs

@@ -0,0 +1,273 @@
+using Node = System.Func<MrGameEng.Formulas.IFormulaContext, float>;
+
+namespace MrGameEng.Formulas;
+
+/// <summary>
+/// Recursive-descent parser that compiles a token list straight into a tree of <see cref="Node"/>
+/// delegates. Parsing (and therefore all closure allocation) happens once; evaluating the returned
+/// node is allocation-free. Precedence, low to high: ternary, <c>||</c>, <c>&amp;&amp;</c>, equality,
+/// comparison, additive, multiplicative, unary, primary.
+/// </summary>
+internal sealed class FormulaParser(List<Token> tokens)
+{
+    private const float True = 1f;
+    private const float False = 0f;
+
+    private int _pos;
+
+    public Node ParseProgram()
+    {
+        var node = ParseTernary();
+        Expect(TokenType.End);
+        return node;
+    }
+
+    private Node ParseTernary()
+    {
+        var condition = ParseOr();
+        if (!Match(TokenType.Question))
+        {
+            return condition;
+        }
+
+        var whenTrue = ParseTernary();
+        Expect(TokenType.Colon);
+        var whenFalse = ParseTernary();
+        return ctx => condition(ctx) != False ? whenTrue(ctx) : whenFalse(ctx);
+    }
+
+    private Node ParseOr()
+    {
+        var left = ParseAnd();
+        while (Match(TokenType.Or))
+        {
+            var right = ParseAnd();
+            var l = left;
+            left = ctx => l(ctx) != False || right(ctx) != False ? True : False;
+        }
+
+        return left;
+    }
+
+    private Node ParseAnd()
+    {
+        var left = ParseEquality();
+        while (Match(TokenType.And))
+        {
+            var right = ParseEquality();
+            var l = left;
+            left = ctx => l(ctx) != False && right(ctx) != False ? True : False;
+        }
+
+        return left;
+    }
+
+    private Node ParseEquality()
+    {
+        var left = ParseComparison();
+        while (true)
+        {
+            if (Match(TokenType.EqualEqual))
+            {
+                var right = ParseComparison();
+                var l = left;
+                left = ctx => l(ctx) == right(ctx) ? True : False;
+            }
+            else if (Match(TokenType.NotEqual))
+            {
+                var right = ParseComparison();
+                var l = left;
+                left = ctx => l(ctx) != right(ctx) ? True : False;
+            }
+            else
+            {
+                return left;
+            }
+        }
+    }
+
+    private Node ParseComparison()
+    {
+        var left = ParseAdditive();
+        while (true)
+        {
+            if (Match(TokenType.Less))
+            {
+                left = Compare(left, ParseAdditive(), (a, b) => a < b);
+            }
+            else if (Match(TokenType.LessEqual))
+            {
+                left = Compare(left, ParseAdditive(), (a, b) => a <= b);
+            }
+            else if (Match(TokenType.Greater))
+            {
+                left = Compare(left, ParseAdditive(), (a, b) => a > b);
+            }
+            else if (Match(TokenType.GreaterEqual))
+            {
+                left = Compare(left, ParseAdditive(), (a, b) => a >= b);
+            }
+            else
+            {
+                return left;
+            }
+        }
+    }
+
+    private Node ParseAdditive()
+    {
+        var left = ParseMultiplicative();
+        while (true)
+        {
+            if (Match(TokenType.Plus))
+            {
+                var right = ParseMultiplicative();
+                var l = left;
+                left = ctx => l(ctx) + right(ctx);
+            }
+            else if (Match(TokenType.Minus))
+            {
+                var right = ParseMultiplicative();
+                var l = left;
+                left = ctx => l(ctx) - right(ctx);
+            }
+            else
+            {
+                return left;
+            }
+        }
+    }
+
+    private Node ParseMultiplicative()
+    {
+        var left = ParseUnary();
+        while (true)
+        {
+            if (Match(TokenType.Star))
+            {
+                var right = ParseUnary();
+                var l = left;
+                left = ctx => l(ctx) * right(ctx);
+            }
+            else if (Match(TokenType.Slash))
+            {
+                var right = ParseUnary();
+                var l = left;
+                left = ctx => l(ctx) / right(ctx);
+            }
+            else if (Match(TokenType.Percent))
+            {
+                var right = ParseUnary();
+                var l = left;
+                left = ctx => l(ctx) % right(ctx);
+            }
+            else
+            {
+                return left;
+            }
+        }
+    }
+
+    private Node ParseUnary()
+    {
+        if (Match(TokenType.Minus))
+        {
+            var operand = ParseUnary();
+            return ctx => -operand(ctx);
+        }
+
+        if (Match(TokenType.Plus))
+        {
+            return ParseUnary();
+        }
+
+        if (Match(TokenType.Not))
+        {
+            var operand = ParseUnary();
+            return ctx => operand(ctx) != False ? False : True;
+        }
+
+        return ParsePrimary();
+    }
+
+    private Node ParsePrimary()
+    {
+        var token = Current;
+        if (Match(TokenType.Number))
+        {
+            var value = token.Number;
+            return _ => value;
+        }
+
+        if (Match(TokenType.LParen))
+        {
+            var inner = ParseTernary();
+            Expect(TokenType.RParen);
+            return inner;
+        }
+
+        if (Match(TokenType.Identifier))
+        {
+            return Peek(TokenType.LParen) ? ParseCall(token.Text) : ParseName(token.Text);
+        }
+
+        throw new FormulaException($"Unexpected token at position {token.Position}.");
+    }
+
+    private Node ParseName(string name)
+    {
+        switch (name)
+        {
+            case "pi":
+                return _ => MathF.PI;
+            case "tau":
+                return _ => MathF.Tau;
+            case "e":
+                return _ => MathF.E;
+            default:
+                return ctx => ctx.Resolve(name);
+        }
+    }
+
+    private Node ParseCall(string name)
+    {
+        Expect(TokenType.LParen);
+        var args = new List<Node>();
+        if (!Peek(TokenType.RParen))
+        {
+            do
+            {
+                args.Add(ParseTernary());
+            } while (Match(TokenType.Comma));
+        }
+
+        Expect(TokenType.RParen);
+        return FormulaFunctions.Build(name, args);
+    }
+
+    private static Node Compare(Node left, Node right, Func<float, float, bool> op) =>
+        ctx => op(left(ctx), right(ctx)) ? True : False;
+
+    private Token Current => tokens[_pos];
+
+    private bool Peek(TokenType type) => Current.Type == type;
+
+    private bool Match(TokenType type)
+    {
+        if (Current.Type != type)
+        {
+            return false;
+        }
+
+        _pos++;
+        return true;
+    }
+
+    private void Expect(TokenType type)
+    {
+        if (!Match(type))
+        {
+            throw new FormulaException($"Expected {type} at position {Current.Position}.");
+        }
+    }
+}

src/MrGameEng.Core/GameClock.cs

@@ -2,7 +2,7 @@ namespace MrGameEng.Core;
 
 /// <summary>
 /// Engine time service: per-frame delta, total elapsed time, time scaling and frame counter.
-/// Advanced once per frame by <see cref="GameHost"/>.
+/// Advanced once per frame (or per fixed tick) by the host.
 /// </summary>
 public sealed class GameClock
 {

src/MrGameEng.Core/HeadlessHost.cs

@@ -0,0 +1,107 @@
+using System.Diagnostics;
+
+namespace MrGameEng.Core;
+
+/// <summary>
+/// A game-loop host without a window, GPU or any platform dependency: drives the active
+/// scene's update phase on a fixed timestep. Suits dedicated servers, batch simulation and
+/// tests. Scenes still own draw systems — they are simply never run, and platform services
+/// (graphics device, window) are absent from <see cref="EngineContext.Services"/>, so only
+/// platform-free modules can be used. The fixed step makes simulation time independent of
+/// wall-clock jitter: N ticks always advance the world by exactly N ×
+/// <see cref="FixedDeltaTime"/> seconds.
+/// </summary>
+public sealed class HeadlessHost : IDisposable
+{
+    /// <summary>Engine context shared with scenes and systems.</summary>
+    public EngineContext Context { get; } = new();
+
+    /// <summary>Fixed simulation step in seconds: 1 / <see cref="HeadlessHostOptions.TicksPerSecond"/>.</summary>
+    public float FixedDeltaTime { get; }
+
+    /// <summary>Ticks completed since the host was created.</summary>
+    public long TickCount => Context.Clock.FrameCount;
+
+    // Отстав сильнее этого, Run ресинкается с настоящим временем вместо лавины тиков.
+    private const double MaxLagSeconds = 1.0;
+
+    private readonly HeadlessHostOptions _options;
+
+    /// <summary>Creates a host that starts with <paramref name="initialScene"/>. The scene
+    /// loads on the first tick, mirroring the windowed host's deferred switch.</summary>
+    public HeadlessHost(HeadlessHostOptions options, Scene initialScene)
+    {
+        if (options.TicksPerSecond <= 0f)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(options),
+                "TicksPerSecond must be positive."
+            );
+        }
+
+        _options = options;
+        FixedDeltaTime = 1f / options.TicksPerSecond;
+        Context.Scenes.Switch(initialScene);
+    }
+
+    /// <summary>Advances the world by exactly one fixed tick.</summary>
+    public void Tick()
+    {
+        Context.Clock.Advance(FixedDeltaTime);
+        Context.Scenes.Update(Context.Clock);
+    }
+
+    /// <summary>Advances the world by <paramref name="count"/> ticks as fast as possible.</summary>
+    public void RunTicks(long count)
+    {
+        for (long i = 0; i < count; i++)
+        {
+            Tick();
+        }
+    }
+
+    /// <summary>
+    /// Runs until <paramref name="cancellationToken"/> is cancelled. With
+    /// <see cref="HeadlessHostOptions.Realtime"/> ticks are paced to the wall clock — the
+    /// loop sleeps when ahead and, having fallen more than a second behind, resyncs instead
+    /// of bursting a catch-up avalanche. Pacing relies on <see cref="Thread.Sleep(TimeSpan)"/>
+    /// and is accurate to a few milliseconds, not exact.
+    /// </summary>
+    public void Run(CancellationToken cancellationToken = default)
+    {
+        if (!_options.Realtime)
+        {
+            while (!cancellationToken.IsCancellationRequested)
+            {
+                Tick();
+            }
+
+            return;
+        }
+
+        var wallClock = Stopwatch.StartNew();
+        var nextTickAt = 0.0;
+        while (!cancellationToken.IsCancellationRequested)
+        {
+            Tick();
+            nextTickAt += FixedDeltaTime;
+            var ahead = nextTickAt - wallClock.Elapsed.TotalSeconds;
+            if (ahead > 0)
+            {
+                Thread.Sleep(TimeSpan.FromSeconds(ahead));
+            }
+            else if (-ahead > MaxLagSeconds)
+            {
+                nextTickAt = wallClock.Elapsed.TotalSeconds;
+            }
+        }
+    }
+
+    /// <summary>Unloads the active scene and disposes context-owned services.</summary>
+    public void Dispose()
+    {
+        Context.Scenes.Switch(null);
+        Context.Scenes.ApplyPending();
+        Context.DisposeOwnedResources();
+    }
+}

src/MrGameEng.Core/HeadlessHostOptions.cs

@@ -0,0 +1,15 @@
+namespace MrGameEng.Core;
+
+/// <summary>Loop settings for <see cref="HeadlessHost"/>.</summary>
+public sealed class HeadlessHostOptions
+{
+    /// <summary>Fixed simulation rate in ticks per second. Must be positive.</summary>
+    public float TicksPerSecond { get; set; } = 60f;
+
+    /// <summary>
+    /// When true, <see cref="HeadlessHost.Run"/> paces ticks to the wall clock (a dedicated
+    /// server); when false it runs flat out (batch simulation). <see cref="HeadlessHost.RunTicks"/>
+    /// always runs flat out regardless of this setting.
+    /// </summary>
+    public bool Realtime { get; set; } = true;
+}

src/MrGameEng.Core/MrGameEng.Core.csproj

@@ -4,11 +4,11 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="MonoGame.Framework.DesktopGL" />
     <PackageReference Include="Friflo.Engine.ECS" />
   </ItemGroup>
 
   <ItemGroup>
     <InternalsVisibleTo Include="MrGameEng.Core.Tests" />
+    <InternalsVisibleTo Include="MrGameEng.Host" />
   </ItemGroup>
 </Project>

src/MrGameEng.Core/SceneManager.cs

@@ -22,13 +22,24 @@ public sealed class SceneManager
     /// <summary>True while a transition is covering or revealing.</summary>
     public bool IsTransitioning => _state != State.Idle;
 
+    /// <summary>The transition currently covering or revealing, or null while idle.
+    /// Hosts that render overlays read this together with <see cref="TransitionCoverage"/>
+    /// and <see cref="TransitionPhase"/> during their draw phase.</summary>
+    public Transition? ActiveTransition => _state == State.Idle ? null : _transition;
+
+    /// <summary>Coverage of the active transition: 0 = scene fully visible, 1 = fully covered.</summary>
+    public float TransitionCoverage => Math.Clamp(_coverage, 0f, 1f);
+
+    /// <summary>Phase of the active transition. Meaningful only while <see cref="IsTransitioning"/>.</summary>
+    public TransitionPhase TransitionPhase =>
+        _state == State.CoveringOut ? TransitionPhase.Out : TransitionPhase.In;
+
     private readonly EngineContext _context;
     private Scene? _pending;
     private bool _hasPending;
     private Transition? _transition;
     private State _state;
     private float _coverage;
-    private TransitionRenderer? _renderer;
 
     internal SceneManager(EngineContext context) => _context = context;
 
@@ -100,27 +111,9 @@ public sealed class SceneManager
         Current?.Update(clock);
     }
 
-    /// <summary>Draws the active scene and the transition overlay on top. Called by the host.</summary>
-    public void Draw(GameClock clock)
-    {
-        Current?.Draw(clock);
-
-        if (_state == State.Idle || !_context.HasGraphicsDevice)
-        {
-            return;
-        }
-
-        _renderer ??= new TransitionRenderer(_context.GraphicsDevice);
-        var phase = _state == State.CoveringOut ? TransitionPhase.Out : TransitionPhase.In;
-        _transition!.Draw(_renderer, Math.Clamp(_coverage, 0f, 1f), phase);
-    }
-
-    /// <summary>Disposes the lazily created transition renderer. Called on host shutdown.</summary>
-    internal void DisposeRenderer()
-    {
-        _renderer?.Dispose();
-        _renderer = null;
-    }
+    /// <summary>Draws the active scene. Transition overlays are rendered by the host on top,
+    /// from <see cref="ActiveTransition"/> and <see cref="TransitionCoverage"/>.</summary>
+    public void Draw(GameClock clock) => Current?.Draw(clock);
 
     internal void ApplyPending()
     {

src/MrGameEng.Core/ServiceRegistry.cs

@@ -40,16 +40,17 @@ public sealed class ServiceRegistry
 
     /// <summary>
     /// Disposes every registered <see cref="IDisposable"/> service (each instance once, even
-    /// when registered under several types) and clears the registry. <paramref name="except"/>
-    /// is skipped. Called on host shutdown.
+    /// when registered under several types) and clears the registry. Instances in
+    /// <paramref name="except"/> are skipped. Called on host shutdown.
     /// </summary>
-    internal void DisposeServices(object? except = null)
+    internal void DisposeServices(params object[] except)
     {
+        var skipped = new HashSet<object>(except, ReferenceEqualityComparer.Instance);
         var disposed = new HashSet<object>(ReferenceEqualityComparer.Instance);
         foreach (var service in _services.Values)
         {
             if (
-                !ReferenceEquals(service, except)
+                !skipped.Contains(service)
                 && service is IDisposable disposable
                 && disposed.Add(service)
             )

src/MrGameEng.Core/Transition.cs

@@ -1,5 +1,3 @@
-using Microsoft.Xna.Framework;
-
 namespace MrGameEng.Core;
 
 /// <summary>Phase of a scene transition.</summary>
@@ -13,10 +11,12 @@ public enum TransitionPhase
 }
 
 /// <summary>
-/// Visual transition between scenes. The scene switch itself happens at full coverage,
-/// so a slow <c>OnLoad</c> of the next scene is hidden behind the overlay.
-/// Transitions are stateless and reusable; progress is tracked by <see cref="SceneManager"/>.
-/// Runs on unscaled time, so it works while gameplay is paused.
+/// Timing of a visual transition between scenes. The scene switch itself happens at full
+/// coverage, so a slow <c>OnLoad</c> of the next scene is hidden behind the overlay.
+/// Progress is tracked by <see cref="SceneManager"/> on unscaled time, so transitions work
+/// while gameplay is paused. The core only times the phases — how the overlay looks is
+/// defined by the host (the MonoGame host's <c>OverlayTransition</c> and the
+/// <c>Transitions</c> factories); headless hosts simply let transitions pass invisibly.
 /// </summary>
 public abstract class Transition
 {
@@ -32,49 +32,4 @@ public abstract class Transition
         OutDuration = Math.Max(0f, outDuration);
         InDuration = Math.Max(0f, inDuration);
     }
-
-    /// <summary>
-    /// Draws the overlay. <paramref name="coverage"/> is 0 (scene fully visible) to
-    /// 1 (scene fully covered); <paramref name="phase"/> tells which side of the switch this is.
-    /// </summary>
-    public abstract void Draw(TransitionRenderer renderer, float coverage, TransitionPhase phase);
-
-    /// <summary>Fade through a solid color (black by default). Total duration is split between out and in.</summary>
-    public static Transition Fade(float duration = 0.6f, Color? color = null) =>
-        new FadeTransition(duration / 2f, duration / 2f, color ?? Color.Black);
-
-    /// <summary>A curtain wiping across the screen (black by default). Total duration is split between out and in.</summary>
-    public static Transition Wipe(float duration = 0.6f, Color? color = null) =>
-        new WipeTransition(duration / 2f, duration / 2f, color ?? Color.Black);
-
-    private sealed class FadeTransition(float outDuration, float inDuration, Color color)
-        : Transition(outDuration, inDuration)
-    {
-        public override void Draw(
-            TransitionRenderer renderer,
-            float coverage,
-            TransitionPhase phase
-        ) => renderer.Fill(0f, 0f, 1f, 1f, color, coverage);
-    }
-
-    private sealed class WipeTransition(float outDuration, float inDuration, Color color)
-        : Transition(outDuration, inDuration)
-    {
-        public override void Draw(
-            TransitionRenderer renderer,
-            float coverage,
-            TransitionPhase phase
-        )
-        {
-            // Out: шторка растёт слева направо; In: уезжает дальше вправо.
-            if (phase == TransitionPhase.Out)
-            {
-                renderer.Fill(0f, 0f, coverage, 1f, color);
-            }
-            else
-            {
-                renderer.Fill(1f - coverage, 0f, coverage, 1f, color);
-            }
-        }
-    }
 }

src/MrGameEng.Graphics/EngineContextGraphicsExtensions.cs

@@ -0,0 +1,19 @@
+using Microsoft.Xna.Framework.Graphics;
+using MrGameEng.Core;
+
+namespace MrGameEng.Graphics;
+
+/// <summary>Graphics-side accessors for the platform-free <see cref="EngineContext"/>.</summary>
+public static class EngineContextGraphicsExtensions
+{
+    /// <summary>
+    /// Returns the <see cref="GraphicsDevice"/> service published by a windowed host.
+    /// Throws in a headless context, where no graphics device exists.
+    /// </summary>
+    public static GraphicsDevice GetGraphicsDevice(this EngineContext context) =>
+        context.Services.GetOrDefault<GraphicsDevice>()
+        ?? throw new InvalidOperationException(
+            "GraphicsDevice is not available: no windowed host has published it "
+                + "(headless context, or graphics are not initialized yet)."
+        );
+}

src/MrGameEng.Graphics/Lighting/Lighting.cs

@@ -0,0 +1,60 @@
+using Microsoft.Xna.Framework;
+using MrGameEng.Core;
+using MrGameEng.Graphics;
+
+namespace MrGameEng.Lighting;
+
+/// <summary>
+/// Scene lighting service: owns the <see cref="Lightmap"/> and exposes a sampleable local light for
+/// the simulation. Built by <see cref="SceneLightmapExtensions.UseLighting"/>, which also registers
+/// the systems that rebuild the lightmap and multiply it over the scene.
+/// </summary>
+public sealed class Lighting
+{
+    /// <summary>The light grid rendered over the world and sampled by the simulation.</summary>
+    public Lightmap Lightmap { get; }
+
+    /// <summary>Creates the service over <paramref name="lightmap"/>.</summary>
+    public Lighting(Lightmap lightmap) => Lightmap = lightmap;
+
+    /// <summary>Local light in <c>[0, 1]</c> at a world point (e.g. for plant growth under canopy).</summary>
+    public float SampleAt(Vector2 world) => Lightmap.SampleAt(world);
+}
+
+/// <summary>Wires the 2D lightmap (day/night × occlusion + point lights) into a <see cref="Scene"/>.</summary>
+public static class SceneLightmapExtensions
+{
+    /// <summary>
+    /// Builds a <see cref="Lighting"/> service for a <paramref name="width"/>×<paramref name="height"/>
+    /// cell world and registers the rebuild and composite systems. Ambient comes from
+    /// <paramref name="dayNight"/>; <paramref name="occluders"/> supplies the current occluder grid
+    /// (row-major, length width×height) each rebuild. Call after <c>UseRenderer2D</c>/<c>UseTilemaps</c>
+    /// and before <c>UseUI</c> so the lightmap composites over the world but under the HUD.
+    /// </summary>
+    public static Lighting UseLighting(
+        this Scene scene,
+        Renderer2D renderer,
+        DayNight dayNight,
+        int width,
+        int height,
+        float cellSize,
+        Vector2 origin,
+        Func<bool[]> occluders
+    )
+    {
+        var device = scene.Context.GetGraphicsDevice();
+        var lightmap = new Lightmap(device, width, height, cellSize, origin);
+        var lighting = new Lighting(lightmap);
+        scene.Context.Services.Add(lighting);
+        RegisterUnloadDispose(scene, lightmap);
+
+        scene.UpdateSystems.Add(
+            new LightmapSystem(scene.Store, lightmap, dayNight, occluders, cellSize, origin)
+        );
+        scene.DrawSystems.Add(new LightmapRenderSystem(device, renderer, lightmap));
+        return lighting;
+    }
+
+    private static void RegisterUnloadDispose(Scene scene, Lightmap lightmap) =>
+        scene.RegisterUnload(lightmap.Dispose);
+}

src/MrGameEng.Graphics/Lighting/Lightmap.cs

@@ -0,0 +1,85 @@
+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+
+namespace MrGameEng.Lighting;
+
+/// <summary>
+/// A per-cell light grid backed by a greyscale <see cref="Texture2D"/>. <see cref="LightmapBuilder"/>
+/// fills <see cref="Light"/>; <see cref="Upload"/> pushes it to the texture (the renderer multiplies
+/// it over the world for soft, cell-resolution shadows); <see cref="SampleAt"/> reads bilinearly for
+/// the simulation (local light at a plant). The grid maps cell (x,y) to world
+/// <c>Origin + (x+0.5, y+0.5)·CellSize</c>.
+/// </summary>
+public sealed class Lightmap : IDisposable
+{
+    /// <summary>Grid width in cells.</summary>
+    public int Width { get; }
+
+    /// <summary>Grid height in cells.</summary>
+    public int Height { get; }
+
+    /// <summary>World size of one cell.</summary>
+    public float CellSize { get; }
+
+    /// <summary>World position of cell (0,0)'s top-left.</summary>
+    public Vector2 Origin { get; }
+
+    /// <summary>Per-cell light in <c>[0, 1]</c>, row-major. Filled by <see cref="LightmapBuilder"/>.</summary>
+    public float[] Light { get; }
+
+    /// <summary>The greyscale light texture (one texel per cell), updated by <see cref="Upload"/>.</summary>
+    public Texture2D Texture { get; }
+
+    private readonly Color[] _pixels;
+
+    /// <summary>Creates a lightmap grid and its backing texture on <paramref name="device"/>.</summary>
+    public Lightmap(GraphicsDevice device, int width, int height, float cellSize, Vector2 origin)
+    {
+        Width = width;
+        Height = height;
+        CellSize = cellSize;
+        Origin = origin;
+        Light = new float[width * height];
+        _pixels = new Color[width * height];
+        Texture = new Texture2D(device, width, height);
+        Array.Fill(Light, 1f);
+        Upload();
+    }
+
+    /// <summary>Writes the current <see cref="Light"/> grid into the texture as greyscale.</summary>
+    public void Upload()
+    {
+        for (var i = 0; i < Light.Length; i++)
+        {
+            var b = (byte)(Math.Clamp(Light[i], 0f, 1f) * 255f);
+            _pixels[i] = new Color(b, b, b, (byte)255);
+        }
+
+        Texture.SetData(_pixels);
+    }
+
+    /// <summary>Bilinearly samples the light at a world point; clamps at the edges.</summary>
+    public float SampleAt(Vector2 world)
+    {
+        var fx = (world.X - Origin.X) / CellSize - 0.5f;
+        var fy = (world.Y - Origin.Y) / CellSize - 0.5f;
+        fx = Math.Clamp(fx, 0f, Width - 1f);
+        fy = Math.Clamp(fy, 0f, Height - 1f);
+
+        var x0 = (int)fx;
+        var y0 = (int)fy;
+        var x1 = Math.Min(x0 + 1, Width - 1);
+        var y1 = Math.Min(y0 + 1, Height - 1);
+        var tx = fx - x0;
+        var ty = fy - y0;
+
+        var top = Lerp(Light[y0 * Width + x0], Light[y0 * Width + x1], tx);
+        var bottom = Lerp(Light[y1 * Width + x0], Light[y1 * Width + x1], tx);
+        return Lerp(top, bottom, ty);
+    }
+
+    private static float Lerp(float a, float b, float t) => a + (b - a) * t;
+
+    /// <inheritdoc />
+    public void Dispose() => Texture.Dispose();
+}

src/MrGameEng.Graphics/Lighting/LightmapBuilder.cs

@@ -0,0 +1,120 @@
+namespace MrGameEng.Lighting;
+
+/// <summary>One point light projected onto the light grid: a cell position, a radius in cells and an intensity.</summary>
+public readonly record struct LightSample(int X, int Y, float Radius, float Intensity);
+
+/// <summary>
+/// Builds a per-cell light grid (CPU, GPU-free, testable): an ambient base dimmed under occluders,
+/// plus point lights that attenuate with distance and are blocked by occluders between the source
+/// and the cell (grid-traced shadows). Pure data — a <see cref="Lightmap"/> turns the grid into a
+/// texture and the simulation samples it for local light.
+/// </summary>
+public static class LightmapBuilder
+{
+    /// <summary>How much of the ambient light reaches a cell that is itself an occluder (canopy/shade).</summary>
+    public const float OccluderShade = 0.35f;
+
+    /// <summary>
+    /// Fills <paramref name="light"/> (length <paramref name="width"/>×<paramref name="height"/>) with
+    /// ambient light, shading occluder cells, then adds each point light with grid-traced occlusion.
+    /// Values end clamped to <c>[0, 1]</c>.
+    /// </summary>
+    public static void Build(
+        float[] light,
+        int width,
+        int height,
+        float ambient,
+        ReadOnlySpan<bool> occluders,
+        IReadOnlyList<LightSample> lights
+    )
+    {
+        for (var i = 0; i < light.Length; i++)
+        {
+            light[i] = occluders[i] ? ambient * OccluderShade : ambient;
+        }
+
+        foreach (var l in lights)
+        {
+            if (l.Radius <= 0f || l.Intensity <= 0f)
+            {
+                continue;
+            }
+
+            var r = (int)MathF.Ceiling(l.Radius);
+            var minX = Math.Max(0, l.X - r);
+            var maxX = Math.Min(width - 1, l.X + r);
+            var minY = Math.Max(0, l.Y - r);
+            var maxY = Math.Min(height - 1, l.Y + r);
+            for (var y = minY; y <= maxY; y++)
+            {
+                for (var x = minX; x <= maxX; x++)
+                {
+                    var dx = x - l.X;
+                    var dy = y - l.Y;
+                    var d = MathF.Sqrt(dx * dx + dy * dy);
+                    if (d > l.Radius)
+                    {
+                        continue;
+                    }
+
+                    if (!Visible(l.X, l.Y, x, y, occluders, width))
+                    {
+                        continue; // в тени за препятствием
+                    }
+
+                    light[y * width + x] += l.Intensity * (1f - d / l.Radius);
+                }
+            }
+        }
+
+        for (var i = 0; i < light.Length; i++)
+        {
+            light[i] = Math.Clamp(light[i], 0f, 1f);
+        }
+    }
+
+    // Есть ли прямая видимость между клетками: проводим линию (Брезенхем) и проверяем
+    // промежуточные клетки на окклюдер (концы исключены).
+    private static bool Visible(
+        int x0,
+        int y0,
+        int x1,
+        int y1,
+        ReadOnlySpan<bool> occluders,
+        int width
+    )
+    {
+        var dx = Math.Abs(x1 - x0);
+        var dy = Math.Abs(y1 - y0);
+        var sx = x0 < x1 ? 1 : -1;
+        var sy = y0 < y1 ? 1 : -1;
+        var err = dx - dy;
+        var x = x0;
+        var y = y0;
+        while (true)
+        {
+            if (x == x1 && y == y1)
+            {
+                return true;
+            }
+
+            if ((x != x0 || y != y0) && occluders[y * width + x])
+            {
+                return false;
+            }
+
+            var e2 = 2 * err;
+            if (e2 > -dy)
+            {
+                err -= dy;
+                x += sx;
+            }
+
+            if (e2 < dx)
+            {
+                err += dx;
+                y += sy;
+            }
+        }
+    }
+}

src/MrGameEng.Graphics/Lighting/LightmapSystems.cs

@@ -0,0 +1,164 @@
+using Friflo.Engine.ECS;
+using Friflo.Engine.ECS.Systems;
+using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+using MrGameEng.Graphics;
+
+namespace MrGameEng.Lighting;
+
+/// <summary>
+/// Rebuilds the lightmap a few times a second: ambient from the day/night cycle, occluder cells from
+/// the game-supplied grid and point lights from the ECS, then uploads it to the texture. Throttled by
+/// frame skipping — the light changes slowly, so 10 Hz looks smooth and keeps cost low.
+/// </summary>
+public sealed class LightmapSystem : BaseSystem
+{
+    private const int RebuildEvery = 6; // ~10 Гц при 60 fps
+    private const float NightFloor = 0.18f; // ночь тусклая, но не чёрная (лунный свет)
+
+    private readonly Lightmap _lightmap;
+    private readonly DayNight _dayNight;
+    private readonly Func<bool[]> _occluders;
+    private readonly float _cellSize;
+    private readonly Vector2 _origin;
+    private readonly ArchetypeQuery<Transform2D, PointLight> _query;
+    private readonly List<LightSample> _lights = [];
+    private int _frame;
+
+    internal LightmapSystem(
+        EntityStore store,
+        Lightmap lightmap,
+        DayNight dayNight,
+        Func<bool[]> occluders,
+        float cellSize,
+        Vector2 origin
+    )
+    {
+        _lightmap = lightmap;
+        _dayNight = dayNight;
+        _occluders = occluders;
+        _cellSize = cellSize;
+        _origin = origin;
+        _query = store.Query<Transform2D, PointLight>();
+    }
+
+    /// <inheritdoc />
+    protected override void OnUpdateGroup()
+    {
+        if (++_frame < RebuildEvery)
+        {
+            return;
+        }
+
+        _frame = 0;
+
+        _lights.Clear();
+        foreach (var (transforms, lights, _) in _query.Chunks)
+        {
+            var t = transforms.Span;
+            var l = lights.Span;
+            for (var i = 0; i < t.Length; i++)
+            {
+                if (l[i].Radius <= 0f || l[i].Intensity <= 0f)
+                {
+                    continue;
+                }
+
+                var cx = (int)((t[i].Position.X - _origin.X) / _cellSize);
+                var cy = (int)((t[i].Position.Y - _origin.Y) / _cellSize);
+                _lights.Add(new LightSample(cx, cy, l[i].Radius / _cellSize, l[i].Intensity));
+            }
+        }
+
+        var ambient = NightFloor + (1f - NightFloor) * _dayNight.Intensity;
+        LightmapBuilder.Build(
+            _lightmap.Light,
+            _lightmap.Width,
+            _lightmap.Height,
+            ambient,
+            _occluders(),
+            _lights
+        );
+        _lightmap.Upload();
+    }
+}
+
+/// <summary>
+/// Draws the lightmap over the world as a single texture quad with multiply blending and linear
+/// filtering — the world darkens by the grid and shadows read soft. Registered after the sprite flush
+/// (so it lands on the drawn scene) and before the screen-space UI (so the HUD stays at full brightness).
+/// </summary>
+public sealed class LightmapRenderSystem : BaseSystem
+{
+    private static readonly BlendState Multiply = new()
+    {
+        ColorSourceBlend = Blend.DestinationColor,
+        ColorDestinationBlend = Blend.Zero,
+        AlphaSourceBlend = Blend.DestinationAlpha,
+        AlphaDestinationBlend = Blend.Zero,
+    };
+
+    private readonly GraphicsDevice _device;
+    private readonly Renderer2D _renderer;
+    private readonly Lightmap _lightmap;
+    private readonly BasicEffect _effect;
+    private readonly VertexPositionTexture[] _quad;
+
+    internal LightmapRenderSystem(GraphicsDevice device, Renderer2D renderer, Lightmap lightmap)
+    {
+        _device = device;
+        _renderer = renderer;
+        _lightmap = lightmap;
+        _effect = new BasicEffect(device)
+        {
+            TextureEnabled = true,
+            VertexColorEnabled = false,
+            World = Matrix.Identity,
+        };
+
+        var x0 = lightmap.Origin.X;
+        var y0 = lightmap.Origin.Y;
+        var x1 = x0 + lightmap.Width * lightmap.CellSize;
+        var y1 = y0 + lightmap.Height * lightmap.CellSize;
+        _quad =
+        [
+            new VertexPositionTexture(new Vector3(x0, y0, 0f), new Vector2(0f, 0f)),
+            new VertexPositionTexture(new Vector3(x1, y0, 0f), new Vector2(1f, 0f)),
+            new VertexPositionTexture(new Vector3(x0, y1, 0f), new Vector2(0f, 1f)),
+            new VertexPositionTexture(new Vector3(x1, y0, 0f), new Vector2(1f, 0f)),
+            new VertexPositionTexture(new Vector3(x1, y1, 0f), new Vector2(1f, 1f)),
+            new VertexPositionTexture(new Vector3(x0, y1, 0f), new Vector2(0f, 1f)),
+        ];
+    }
+
+    /// <inheritdoc />
+    protected override void OnUpdateGroup()
+    {
+        var camera = _renderer.Camera;
+        _effect.View = camera.View;
+        _effect.Projection = camera.Projection;
+        _effect.Texture = _lightmap.Texture;
+
+        var previousViewport = _device.Viewport;
+        var mapping = camera.Mapping;
+        _device.Viewport = new Viewport(
+            (int)MathF.Round(mapping.Offset.X),
+            (int)MathF.Round(mapping.Offset.Y),
+            (int)MathF.Round(camera.VirtualWidth * mapping.Scale),
+            (int)MathF.Round(camera.VirtualHeight * mapping.Scale)
+        );
+        _device.BlendState = Multiply;
+        _device.SamplerStates[0] = SamplerState.LinearClamp;
+        _device.DepthStencilState = DepthStencilState.None;
+        _device.RasterizerState = RasterizerState.CullNone;
+
+        foreach (var pass in _effect.CurrentTechnique.Passes)
+        {
+            pass.Apply();
+            _device.DrawUserPrimitives(PrimitiveType.TriangleList, _quad, 0, 2);
+        }
+
+        _device.Viewport = previousViewport;
+        _device.BlendState = BlendState.AlphaBlend;
+    }
+}

src/MrGameEng.Graphics/Lighting/PointLight.cs

@@ -0,0 +1,21 @@
+using Friflo.Engine.ECS;
+using Microsoft.Xna.Framework;
+
+namespace MrGameEng.Lighting;
+
+/// <summary>
+/// A point light: an entity with this component plus a <see cref="MrGameEng.Graphics.Transform2D"/>
+/// adds light around its world position, attenuating to zero at <see cref="Radius"/> and casting
+/// grid-traced shadows behind occluders. Picked up by the lighting system into the lightmap.
+/// </summary>
+public struct PointLight : IComponent
+{
+    /// <summary>Reach of the light in world units (light fades to zero at this distance).</summary>
+    public float Radius;
+
+    /// <summary>Light tint (reserved for colored lights; intensity currently drives brightness).</summary>
+    public Color Color;
+
+    /// <summary>Peak brightness added at the light's centre (0..1+).</summary>
+    public float Intensity;
+}

src/MrGameEng.Graphics/MrGameEng.Graphics.csproj

@@ -1,13 +1,17 @@
-<Project Sdk="Microsoft.NET.Sdk">
-  <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
-  </PropertyGroup>
-
-  <ItemGroup>
-    <InternalsVisibleTo Include="MrGameEng.Graphics.Tests" />
-  </ItemGroup>
-
-  <ItemGroup>
-    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
-  </ItemGroup>
-</Project>
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MonoGame.Framework.DesktopGL" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="MrGameEng.Graphics.Tests" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
+  </ItemGroup>
+</Project>

src/MrGameEng.Graphics/SceneGraphicsExtensions.cs

@@ -22,7 +22,7 @@ public static class SceneGraphicsExtensions
         var renderer = services.GetOrDefault<Renderer2D>();
         if (renderer is null)
         {
-            renderer = new Renderer2D(scene.Context.GraphicsDevice, options);
+            renderer = new Renderer2D(scene.Context.GetGraphicsDevice(), options);
             services.Add(renderer);
         }
         else if (options is not null)

src/MrGameEng.Host/GameHost.cs

@@ -1,11 +1,16 @@
 using Microsoft.Xna.Framework;
+using Microsoft.Xna.Framework.Graphics;
+using MrGameEng.Core;
 
-namespace MrGameEng.Core;
+namespace MrGameEng.Host;
 
 /// <summary>
-/// The engine's game loop host. Wraps MonoGame's <see cref="Game"/>: owns the
-/// <see cref="EngineContext"/>, advances the <see cref="GameClock"/> and drives the
-/// active scene's update and draw phases.
+/// The engine's windowed game-loop host. Wraps MonoGame's <see cref="Game"/>: owns the
+/// <see cref="EngineContext"/>, advances the <see cref="GameClock"/>, drives the active
+/// scene's update and draw phases and renders scene-transition overlays. The
+/// <see cref="GraphicsDevice"/> is published as a service so graphics modules can reach it
+/// through the context. For a loop without a window or GPU see
+/// <see cref="HeadlessHost"/> in the core.
 /// </summary>
 public class GameHost : Game
 {
@@ -17,6 +22,7 @@ public class GameHost : Game
 
     private readonly GameHostOptions _options;
     private readonly Scene _initialScene;
+    private TransitionRenderer? _transitionRenderer;
 
     /// <summary>Creates a host that starts with <paramref name="initialScene"/>.</summary>
     public GameHost(GameHostOptions options, Scene initialScene)
@@ -48,7 +54,7 @@ public class GameHost : Game
     {
         Window.Title = _options.Title;
         Window.AllowUserResizing = _options.AllowResizing;
-        Context.AttachGraphicsDevice(GraphicsDevice);
+        Context.Services.Add(GraphicsDevice);
         Context.Services.Add(Window);
         Context.Services.Add<Game>(this);
         base.Initialize();
@@ -68,9 +74,25 @@ public class GameHost : Game
     {
         GraphicsDevice.Clear(_options.ClearColor);
         Context.Scenes.Draw(Context.Clock);
+        DrawTransitionOverlay();
         base.Draw(gameTime);
     }
 
+    private void DrawTransitionOverlay()
+    {
+        if (Context.Scenes.ActiveTransition is not OverlayTransition transition)
+        {
+            return;
+        }
+
+        _transitionRenderer ??= new TransitionRenderer(GraphicsDevice);
+        transition.Draw(
+            _transitionRenderer,
+            Context.Scenes.TransitionCoverage,
+            Context.Scenes.TransitionPhase
+        );
+    }
+
     /// <inheritdoc />
     protected override void OnExiting(object sender, ExitingEventArgs args)
     {
@@ -84,7 +106,11 @@ public class GameHost : Game
     {
         if (disposing)
         {
-            Context.DisposeOwnedResources(except: this);
+            _transitionRenderer?.Dispose();
+            _transitionRenderer = null;
+            // GraphicsDevice зарегистрирован как сервис, но им владеет MonoGame:
+            // base.Dispose сам его освобождает, реестру трогать нельзя.
+            Context.DisposeOwnedResources(this, GraphicsDevice);
         }
 
         base.Dispose(disposing);

src/MrGameEng.Host/GameHostOptions.cs

@@ -1,6 +1,6 @@
 using Microsoft.Xna.Framework;
 
-namespace MrGameEng.Core;
+namespace MrGameEng.Host;
 
 /// <summary>Window and loop settings for <see cref="GameHost"/>.</summary>
 public sealed class GameHostOptions

src/MrGameEng.Host/MrGameEng.Host.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="MonoGame.Framework.DesktopGL" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="MrGameEng.Host.Tests" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
+  </ItemGroup>
+</Project>

src/MrGameEng.Host/TransitionRenderer.cs

@@ -1,11 +1,11 @@
 using Microsoft.Xna.Framework;
 using Microsoft.Xna.Framework.Graphics;
 
-namespace MrGameEng.Core;
+namespace MrGameEng.Host;
 
 /// <summary>
-/// Minimal overlay renderer handed to <see cref="Transition.Draw"/>: fills rectangles in
-/// normalized screen coordinates (0..1 on both axes) over the rendered scene.
+/// Minimal overlay renderer handed to <see cref="OverlayTransition.Draw"/>: fills rectangles
+/// in normalized screen coordinates (0..1 on both axes) over the rendered scene.
 /// </summary>
 public sealed class TransitionRenderer : IDisposable
 {
@@ -13,7 +13,7 @@ public sealed class TransitionRenderer : IDisposable
     private readonly BasicEffect _effect;
     private readonly VertexPositionColor[] _vertices = new VertexPositionColor[6];
 
-    /// <summary>Disposes the GPU effect. Called by <see cref="SceneManager"/> on shutdown.</summary>
+    /// <summary>Disposes the GPU effect. Called by <see cref="GameHost"/> on shutdown.</summary>
     public void Dispose() => _effect.Dispose();
 
     internal TransitionRenderer(GraphicsDevice device)

src/MrGameEng.Host/Transitions.cs

@@ -0,0 +1,66 @@
+using Microsoft.Xna.Framework;
+using MrGameEng.Core;
+
+namespace MrGameEng.Host;
+
+/// <summary>
+/// A scene transition that draws a full-screen overlay through a
+/// <see cref="TransitionRenderer"/>. The timing state machine lives in
+/// <see cref="SceneManager"/>; <see cref="GameHost"/> renders the overlay each draw while a
+/// transition is active. Transitions are stateless and reusable.
+/// </summary>
+public abstract class OverlayTransition : Transition
+{
+    /// <summary>Creates a transition with explicit phase durations.</summary>
+    protected OverlayTransition(float outDuration, float inDuration)
+        : base(outDuration, inDuration) { }
+
+    /// <summary>
+    /// Draws the overlay. <paramref name="coverage"/> is 0 (scene fully visible) to
+    /// 1 (scene fully covered); <paramref name="phase"/> tells which side of the switch this is.
+    /// </summary>
+    public abstract void Draw(TransitionRenderer renderer, float coverage, TransitionPhase phase);
+}
+
+/// <summary>Factories for the built-in visual scene transitions.</summary>
+public static class Transitions
+{
+    /// <summary>Fade through a solid color (black by default). Total duration is split between out and in.</summary>
+    public static Transition Fade(float duration = 0.6f, Color? color = null) =>
+        new FadeTransition(duration / 2f, duration / 2f, color ?? Color.Black);
+
+    /// <summary>A curtain wiping across the screen (black by default). Total duration is split between out and in.</summary>
+    public static Transition Wipe(float duration = 0.6f, Color? color = null) =>
+        new WipeTransition(duration / 2f, duration / 2f, color ?? Color.Black);
+
+    private sealed class FadeTransition(float outDuration, float inDuration, Color color)
+        : OverlayTransition(outDuration, inDuration)
+    {
+        public override void Draw(
+            TransitionRenderer renderer,
+            float coverage,
+            TransitionPhase phase
+        ) => renderer.Fill(0f, 0f, 1f, 1f, color, coverage);
+    }
+
+    private sealed class WipeTransition(float outDuration, float inDuration, Color color)
+        : OverlayTransition(outDuration, inDuration)
+    {
+        public override void Draw(
+            TransitionRenderer renderer,
+            float coverage,
+            TransitionPhase phase
+        )
+        {
+            // Out: шторка растёт слева направо; In: уезжает дальше вправо.
+            if (phase == TransitionPhase.Out)
+            {
+                renderer.Fill(0f, 0f, coverage, 1f, color);
+            }
+            else
+            {
+                renderer.Fill(1f - coverage, 0f, coverage, 1f, color);
+            }
+        }
+    }
+}

src/MrGameEng.Net/INetConnection.cs

@@ -0,0 +1,25 @@
+namespace MrGameEng.Net;
+
+/// <summary>
+/// A bidirectional, reliable, ordered binary message channel (a WebSocket under the hood).
+/// Receiving is poll-based to fit the simulation loop: incoming messages queue up on a
+/// background reader and are drained with <see cref="TryReceive"/> from the tick. Sending
+/// never blocks the caller. Implementations are safe to use from one simulation thread.
+/// </summary>
+public interface INetConnection
+{
+    /// <summary>Connection id, unique within its owner (server-assigned; 0 for a client's own connection).</summary>
+    int Id { get; }
+
+    /// <summary>False once the peer disconnected or the connection failed; sends become no-ops.</summary>
+    bool IsOpen { get; }
+
+    /// <summary>Queues one binary message for delivery. No-op when the connection is closed.</summary>
+    void Send(ReadOnlySpan<byte> message);
+
+    /// <summary>Dequeues the next received binary message, if any.</summary>
+    bool TryReceive(out byte[] message);
+
+    /// <summary>Closes the connection.</summary>
+    void Close();
+}

src/MrGameEng.Net/MrGameEng.Net.csproj

@@ -0,0 +1,18 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Friflo.Engine.ECS" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="MrGameEng.Net.Tests" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
+  </ItemGroup>
+</Project>

src/MrGameEng.Net/Replication/NetId.cs

@@ -0,0 +1,14 @@
+using Friflo.Engine.ECS;
+
+namespace MrGameEng.Net;
+
+/// <summary>
+/// Marks an entity as replicated and identifies it across the network. The server assigns
+/// values (see <see cref="ReplicationServer.NextNetId"/>); the client creates a local
+/// entity with the same <see cref="Value"/> when the first snapshot arrives.
+/// </summary>
+public struct NetId : IComponent
+{
+    /// <summary>Network-wide entity id, unique per server world.</summary>
+    public int Value;
+}

src/MrGameEng.Net/Replication/ReplicationClient.cs

@@ -0,0 +1,92 @@
+using Friflo.Engine.ECS;
+
+namespace MrGameEng.Net;
+
+/// <summary>
+/// Client side of replication: applies snapshot messages from a
+/// <see cref="ReplicationServer"/> to a local <see cref="EntityStore"/>. Unknown net ids
+/// spawn local entities (carrying <see cref="NetId"/>), known ones get their changed
+/// components overwritten, despawns delete. The game decorates replicated entities with
+/// presentation components (sprites etc.) on top — replication never touches types outside
+/// its <see cref="ReplicationSchema"/>.
+/// </summary>
+public sealed class ReplicationClient
+{
+    /// <summary>Number of replicated entities currently alive locally.</summary>
+    public int EntityCount => _entities.Count;
+
+    /// <summary>Raised after an entity is created from a snapshot. Hook presentation setup here.</summary>
+    public event Action<Entity>? EntitySpawned;
+
+    private readonly ReplicationSchema _schema;
+    private readonly EntityStore _store;
+    private readonly Dictionary<int, Entity> _entities = [];
+
+    /// <summary>Creates a replication client writing into <paramref name="store"/>.</summary>
+    public ReplicationClient(ReplicationSchema schema, EntityStore store)
+    {
+        _schema = schema;
+        _store = store;
+    }
+
+    /// <summary>Applies every message queued on <paramref name="connection"/>.</summary>
+    public void Pump(INetConnection connection)
+    {
+        while (connection.TryReceive(out var message))
+        {
+            Apply(message);
+        }
+    }
+
+    /// <summary>Applies one snapshot message to the local store.</summary>
+    public void Apply(byte[] message)
+    {
+        using var reader = new BinaryReader(new MemoryStream(message));
+        if (reader.ReadByte() != ReplicationMessage.Snapshot)
+        {
+            return; // незнакомый тип сообщения — пропускаем, это не снапшот
+        }
+
+        var slots = _schema.Slots;
+        var count = reader.ReadInt32();
+        for (var record = 0; record < count; record++)
+        {
+            var netId = reader.ReadInt32();
+            var op = reader.ReadByte();
+            if (op == ReplicationMessage.OpDespawn)
+            {
+                if (_entities.Remove(netId, out var dead))
+                {
+                    dead.DeleteEntity();
+                }
+
+                continue;
+            }
+
+            var mask = reader.ReadUInt32();
+            var spawned = false;
+            if (!_entities.TryGetValue(netId, out var entity))
+            {
+                entity = _store.CreateEntity(new NetId { Value = netId });
+                _entities[netId] = entity;
+                spawned = true;
+            }
+
+            foreach (var slot in slots)
+            {
+                if ((mask & (1u << slot.Bit)) == 0)
+                {
+                    continue;
+                }
+
+                var data = reader.ReadBytes(slot.Size);
+                slot.Apply(entity, data, 0);
+            }
+
+            if (spawned)
+            {
+                EntitySpawned?.Invoke(entity);
+            }
+        }
+    }
+}

src/MrGameEng.Net/Replication/ReplicationSchema.cs

@@ -0,0 +1,64 @@
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using Friflo.Engine.ECS;
+
+namespace MrGameEng.Net;
+
+/// <summary>
+/// The set of component types a game replicates, registered in the same order on the
+/// server and every client (the order defines the wire ids). Components must be
+/// unmanaged structs — they are blitted to the wire as raw bytes, so server and client
+/// must run on the same engine version. Up to 32 types.
+/// </summary>
+public sealed class ReplicationSchema
+{
+    internal sealed class ComponentSlot
+    {
+        public required int Bit;
+        public required int Size;
+        public required Func<Entity, byte[], bool> TryWrite;
+        public required Action<Entity, byte[], int> Apply;
+    }
+
+    internal readonly List<ComponentSlot> Slots = [];
+
+    /// <summary>
+    /// Registers component type <typeparamref name="T"/> for replication. Returns this
+    /// schema for fluent chaining.
+    /// </summary>
+    public ReplicationSchema Register<T>()
+        where T : unmanaged, IComponent
+    {
+        if (Slots.Count == 32)
+        {
+            throw new InvalidOperationException(
+                "ReplicationSchema supports at most 32 component types."
+            );
+        }
+
+        var size = Unsafe.SizeOf<T>();
+        Slots.Add(
+            new ComponentSlot
+            {
+                Bit = Slots.Count,
+                Size = size,
+                TryWrite = (entity, buffer) =>
+                {
+                    if (!entity.HasComponent<T>())
+                    {
+                        return false;
+                    }
+
+                    MemoryMarshal.Write(buffer, in entity.GetComponent<T>());
+                    return true;
+                },
+                Apply = (entity, data, offset) =>
+                {
+                    var value = MemoryMarshal.Read<T>(data.AsSpan(offset, size));
+                    entity.AddComponent(value);
+                },
+            }
+        );
+        return this;
+    }
+}

src/MrGameEng.Net/Replication/ReplicationServer.cs

@@ -0,0 +1,174 @@
+using Friflo.Engine.ECS;
+
+namespace MrGameEng.Net;
+
+/// <summary>
+/// Server-authoritative component replication. Each call to <see cref="Send"/> snapshots
+/// every entity carrying <see cref="NetId"/> and sends each connection only what changed
+/// since that connection's previous snapshot (per-component deltas; a new connection gets
+/// the full state the same way). Deltas need no acknowledgements because the transport is
+/// reliable and ordered. Call at the desired send rate (e.g. every Nth simulation tick),
+/// from the simulation thread.
+/// </summary>
+public sealed class ReplicationServer
+{
+    private sealed class ConnectionState
+    {
+        // По netId: последний отправленный блоб каждого зарегистрированного компонента.
+        public readonly Dictionary<int, byte[]?[]> LastSent = [];
+    }
+
+    private readonly ReplicationSchema _schema;
+    private readonly ArchetypeQuery<NetId> _query;
+    private readonly Dictionary<INetConnection, ConnectionState> _states = [];
+
+    // Снапшот текущего тика, переиспользуется между соединениями.
+    private readonly List<(int NetId, byte[]?[] Components)> _current = [];
+    private readonly HashSet<int> _currentIds = [];
+    private int _nextNetId;
+
+    /// <summary>Creates a replication server over <paramref name="store"/>.</summary>
+    public ReplicationServer(ReplicationSchema schema, EntityStore store)
+    {
+        _schema = schema;
+        _query = store.Query<NetId>();
+    }
+
+    /// <summary>Allocates the next free network id for a newly spawned replicated entity.</summary>
+    public int NextNetId() => ++_nextNetId;
+
+    /// <summary>
+    /// Snapshots the world once and sends per-connection deltas. Closed connections are
+    /// forgotten; brand-new ones receive the full state.
+    /// </summary>
+    public void Send(IReadOnlyList<INetConnection> connections)
+    {
+        CaptureCurrentState();
+
+        foreach (var connection in connections)
+        {
+            if (!connection.IsOpen)
+            {
+                continue;
+            }
+
+            if (!_states.TryGetValue(connection, out var state))
+            {
+                state = new ConnectionState();
+                _states[connection] = state;
+            }
+
+            var message = BuildDelta(state);
+            if (message is not null)
+            {
+                connection.Send(message);
+            }
+        }
+
+        // Забываем состояние умерших соединений, чтобы не копить мусор.
+        foreach (var dead in _states.Keys.Where(c => !c.IsOpen).ToList())
+        {
+            _states.Remove(dead);
+        }
+    }
+
+    private void CaptureCurrentState()
+    {
+        _current.Clear();
+        _currentIds.Clear();
+        var slots = _schema.Slots;
+        _query.ForEachEntity(
+            (ref NetId netId, Entity entity) =>
+            {
+                var components = new byte[]?[slots.Count];
+                foreach (var slot in slots)
+                {
+                    var buffer = new byte[slot.Size];
+                    components[slot.Bit] = slot.TryWrite(entity, buffer) ? buffer : null;
+                }
+
+                _current.Add((netId.Value, components));
+                _currentIds.Add(netId.Value);
+            }
+        );
+    }
+
+    private byte[]? BuildDelta(ConnectionState state)
+    {
+        using var stream = new MemoryStream();
+        using var writer = new BinaryWriter(stream);
+        writer.Write(ReplicationMessage.Snapshot);
+        var countPosition = stream.Position;
+        writer.Write(0); // количество записей, допишем в конце
+        var records = 0;
+
+        foreach (var (netId, components) in _current)
+        {
+            if (!state.LastSent.TryGetValue(netId, out var lastSent))
+            {
+                lastSent = new byte[]?[components.Length];
+                state.LastSent[netId] = lastSent;
+            }
+
+            uint mask = 0;
+            for (var bit = 0; bit < components.Length; bit++)
+            {
+                var current = components[bit];
+                if (current is null)
+                {
+                    continue;
+                }
+
+                if (lastSent[bit] is null || !current.AsSpan().SequenceEqual(lastSent[bit]))
+                {
+                    mask |= 1u << bit;
+                    lastSent[bit] = current;
+                }
+            }
+
+            if (mask == 0)
+            {
+                continue;
+            }
+
+            writer.Write(netId);
+            writer.Write(ReplicationMessage.OpUpsert);
+            writer.Write(mask);
+            for (var bit = 0; bit < components.Length; bit++)
+            {
+                if ((mask & (1u << bit)) != 0)
+                {
+                    writer.Write(components[bit]!);
+                }
+            }
+
+            records++;
+        }
+
+        // Сущности, которые соединение знает, а в мире их больше нет.
+        foreach (var known in state.LastSent.Keys.Where(id => !_currentIds.Contains(id)).ToList())
+        {
+            state.LastSent.Remove(known);
+            writer.Write(known);
+            writer.Write(ReplicationMessage.OpDespawn);
+            records++;
+        }
+
+        if (records == 0)
+        {
+            return null;
+        }
+
+        stream.Position = countPosition;
+        writer.Write(records);
+        return stream.ToArray();
+    }
+}
+
+/// <summary>Wire constants shared by <see cref="ReplicationServer"/> and <see cref="ReplicationClient"/>.</summary>
+internal static class ReplicationMessage
+{
+    internal const byte Snapshot = 1;
+    internal const byte OpUpsert = 0;
+    internal const byte OpDespawn = 1;
+}

src/MrGameEng.Net/WebSocketClient.cs

@@ -0,0 +1,141 @@
+using System.Collections.Concurrent;
+using System.Net.WebSockets;
+
+namespace MrGameEng.Net;
+
+/// <summary>
+/// Client side of <see cref="INetConnection"/>: a thin wrapper over the BCL
+/// <see cref="ClientWebSocket"/>, which works on desktop and inside Blazor WebAssembly
+/// (where it maps to the browser's WebSocket). Receiving runs on a background task into a
+/// queue; sends are chained fire-and-forget so the caller — and the browser's single
+/// thread — never blocks.
+/// </summary>
+public sealed class WebSocketClient : INetConnection, IDisposable
+{
+    /// <inheritdoc />
+    public int Id => 0;
+
+    /// <inheritdoc />
+    public bool IsOpen => !_closed && _socket.State == WebSocketState.Open;
+
+    private readonly ClientWebSocket _socket;
+    private readonly ConcurrentQueue<byte[]> _inbox = new();
+    private readonly CancellationTokenSource _shutdown = new();
+    private Task _sendTail = Task.CompletedTask;
+    private volatile bool _closed;
+
+    private WebSocketClient(ClientWebSocket socket) => _socket = socket;
+
+    /// <summary>
+    /// Connects to <paramref name="uri"/> (ws:// or wss://) and starts the receive loop.
+    /// </summary>
+    public static async Task<WebSocketClient> ConnectAsync(
+        Uri uri,
+        CancellationToken cancellationToken = default
+    )
+    {
+        var socket = new ClientWebSocket();
+        await socket.ConnectAsync(uri, cancellationToken).ConfigureAwait(false);
+        var client = new WebSocketClient(socket);
+        _ = Task.Run(client.ReceiveLoop);
+        return client;
+    }
+
+    /// <inheritdoc />
+    public void Send(ReadOnlySpan<byte> message)
+    {
+        if (!IsOpen)
+        {
+            return;
+        }
+
+        var copy = message.ToArray();
+        // Отправки сцеплены в хвост: ClientWebSocket не терпит параллельных SendAsync,
+        // а блокировать поток нельзя (в wasm это смерть).
+        lock (_shutdown)
+        {
+            _sendTail = _sendTail.ContinueWith(
+                _ => SendCore(copy),
+                CancellationToken.None,
+                TaskContinuationOptions.None,
+                TaskScheduler.Default
+            );
+        }
+    }
+
+    private async Task SendCore(byte[] message)
+    {
+        try
+        {
+            await _socket
+                .SendAsync(
+                    message,
+                    WebSocketMessageType.Binary,
+                    endOfMessage: true,
+                    _shutdown.Token
+                )
+                .ConfigureAwait(false);
+        }
+        catch (Exception)
+        {
+            Close();
+        }
+    }
+
+    /// <inheritdoc />
+    public bool TryReceive(out byte[] message) => _inbox.TryDequeue(out message!);
+
+    /// <inheritdoc />
+    public void Close()
+    {
+        if (_closed)
+        {
+            return;
+        }
+
+        _closed = true;
+        _shutdown.Cancel();
+        _socket.Dispose();
+    }
+
+    /// <summary>Closes the connection.</summary>
+    public void Dispose() => Close();
+
+    private async Task ReceiveLoop()
+    {
+        var buffer = new byte[64 * 1024];
+        var message = new MemoryStream();
+        try
+        {
+            while (!_closed)
+            {
+                var result = await _socket
+                    .ReceiveAsync(buffer, _shutdown.Token)
+                    .ConfigureAwait(false);
+                if (result.MessageType == WebSocketMessageType.Close)
+                {
+                    break;
+                }
+
+                message.Write(buffer, 0, result.Count);
+                if (result.EndOfMessage)
+                {
+                    if (result.MessageType == WebSocketMessageType.Binary)
+                    {
+                        _inbox.Enqueue(message.ToArray());
+                    }
+
+                    message.SetLength(0);
+                }
+            }
+        }
+        catch (Exception)
+        {
+            // обрыв или закрытие — штатное завершение цикла
+        }
+        finally
+        {
+            Close();
+        }
+    }
+}

src/MrGameEng.Net/WebSocketProtocol.cs

@@ -0,0 +1,248 @@
+using System.Buffers.Binary;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace MrGameEng.Net;
+
+/// <summary>WebSocket frame opcodes used by the server.</summary>
+internal enum WebSocketOpcode : byte
+{
+    Continuation = 0x0,
+    Text = 0x1,
+    Binary = 0x2,
+    Close = 0x8,
+    Ping = 0x9,
+    Pong = 0xA,
+}
+
+/// <summary>
+/// Minimal RFC 6455 building blocks for the server side: the upgrade handshake and frame
+/// encode/decode over a <see cref="Stream"/>. Kept free of sockets so the protocol logic is
+/// unit-testable; <see cref="WebSocketServer"/> wires it to TCP.
+/// </summary>
+internal static class WebSocketProtocol
+{
+    private const string HandshakeGuid = "258EAFA5-E914-47DA-95CA-C5AB0DC85B11";
+
+    /// <summary>Computes the Sec-WebSocket-Accept value for a client's Sec-WebSocket-Key.</summary>
+    internal static string AcceptKey(string secWebSocketKey)
+    {
+        var bytes = Encoding.ASCII.GetBytes(secWebSocketKey + HandshakeGuid);
+        return Convert.ToBase64String(SHA1.HashData(bytes));
+    }
+
+    /// <summary>
+    /// Reads the HTTP upgrade request from <paramref name="stream"/> (up to the blank line)
+    /// and extracts the Sec-WebSocket-Key header. Returns false on a malformed request.
+    /// </summary>
+    internal static bool TryReadHandshakeKey(Stream stream, out string key)
+    {
+        key = "";
+        var buffer = new byte[8 * 1024];
+        var length = 0;
+        // Читаем до конца заголовков (\r\n\r\n); запрос маленький, побайтовое чтение не больно.
+        while (length < buffer.Length)
+        {
+            var read = stream.Read(buffer, length, 1);
+            if (read == 0)
+            {
+                return false;
+            }
+
+            length++;
+            if (
+                length >= 4
+                && buffer[length - 4] == (byte)'\r'
+                && buffer[length - 3] == (byte)'\n'
+                && buffer[length - 2] == (byte)'\r'
+                && buffer[length - 1] == (byte)'\n'
+            )
+            {
+                break;
+            }
+        }
+
+        var request = Encoding.ASCII.GetString(buffer, 0, length);
+        foreach (var line in request.Split("\r\n"))
+        {
+            var separator = line.IndexOf(':');
+            if (separator < 0)
+            {
+                continue;
+            }
+
+            if (
+                line[..separator]
+                    .Trim()
+                    .Equals("Sec-WebSocket-Key", StringComparison.OrdinalIgnoreCase)
+            )
+            {
+                key = line[(separator + 1)..].Trim();
+                return key.Length > 0;
+            }
+        }
+
+        return false;
+    }
+
+    /// <summary>Writes the 101 Switching Protocols response completing the handshake.</summary>
+    internal static void WriteHandshakeResponse(Stream stream, string secWebSocketKey)
+    {
+        var response =
+            "HTTP/1.1 101 Switching Protocols\r\n"
+            + "Upgrade: websocket\r\n"
+            + "Connection: Upgrade\r\n"
+            + $"Sec-WebSocket-Accept: {AcceptKey(secWebSocketKey)}\r\n"
+            + "\r\n";
+        var bytes = Encoding.ASCII.GetBytes(response);
+        stream.Write(bytes, 0, bytes.Length);
+    }
+
+    /// <summary>
+    /// Encodes one complete (FIN) frame. Server frames are unmasked per RFC 6455;
+    /// <paramref name="maskKey"/> is for tests that emulate a client.
+    /// </summary>
+    internal static byte[] EncodeFrame(
+        ReadOnlySpan<byte> payload,
+        WebSocketOpcode opcode,
+        byte[]? maskKey = null
+    )
+    {
+        var masked = maskKey is not null;
+        var headerLength =
+            2
+            + payload.Length switch
+            {
+                <= 125 => 0,
+                <= ushort.MaxValue => 2,
+                _ => 8,
+            };
+        var frame = new byte[headerLength + (masked ? 4 : 0) + payload.Length];
+        frame[0] = (byte)(0x80 | (byte)opcode);
+        switch (payload.Length)
+        {
+            case <= 125:
+                frame[1] = (byte)payload.Length;
+                break;
+            case <= ushort.MaxValue:
+                frame[1] = 126;
+                BinaryPrimitives.WriteUInt16BigEndian(frame.AsSpan(2), (ushort)payload.Length);
+                break;
+            default:
+                frame[1] = 127;
+                BinaryPrimitives.WriteUInt64BigEndian(frame.AsSpan(2), (ulong)payload.Length);
+                break;
+        }
+
+        var offset = headerLength;
+        if (masked)
+        {
+            frame[1] |= 0x80;
+            maskKey!.CopyTo(frame, offset);
+            offset += 4;
+            for (var i = 0; i < payload.Length; i++)
+            {
+                frame[offset + i] = (byte)(payload[i] ^ maskKey[i % 4]);
+            }
+        }
+        else
+        {
+            payload.CopyTo(frame.AsSpan(offset));
+        }
+
+        return frame;
+    }
+
+    /// <summary>
+    /// Reads one frame. Returns false on a clean end of stream. Masked payloads are unmasked.
+    /// </summary>
+    internal static bool TryReadFrame(
+        Stream stream,
+        out WebSocketOpcode opcode,
+        out bool fin,
+        out byte[] payload
+    )
+    {
+        opcode = WebSocketOpcode.Close;
+        fin = true;
+        payload = [];
+
+        var header = new byte[2];
+        if (!TryReadExactly(stream, header))
+        {
+            return false;
+        }
+
+        fin = (header[0] & 0x80) != 0;
+        opcode = (WebSocketOpcode)(header[0] & 0x0F);
+        var masked = (header[1] & 0x80) != 0;
+        long length = header[1] & 0x7F;
+        if (length == 126)
+        {
+            var extended = new byte[2];
+            if (!TryReadExactly(stream, extended))
+            {
+                return false;
+            }
+
+            length = BinaryPrimitives.ReadUInt16BigEndian(extended);
+        }
+        else if (length == 127)
+        {
+            var extended = new byte[8];
+            if (!TryReadExactly(stream, extended))
+            {
+                return false;
+            }
+
+            length = (long)BinaryPrimitives.ReadUInt64BigEndian(extended);
+        }
+
+        if (length > MaxPayloadBytes)
+        {
+            return false; // защита от злонамеренной длины — соединение закроется
+        }
+
+        var maskKey = new byte[4];
+        if (masked && !TryReadExactly(stream, maskKey))
+        {
+            return false;
+        }
+
+        payload = new byte[length];
+        if (!TryReadExactly(stream, payload))
+        {
+            return false;
+        }
+
+        if (masked)
+        {
+            for (var i = 0; i < payload.Length; i++)
+            {
+                payload[i] ^= maskKey[i % 4];
+            }
+        }
+
+        return true;
+    }
+
+    /// <summary>Upper bound for a single frame payload accepted by the server.</summary>
+    internal const int MaxPayloadBytes = 16 * 1024 * 1024;
+
+    private static bool TryReadExactly(Stream stream, byte[] buffer)
+    {
+        var offset = 0;
+        while (offset < buffer.Length)
+        {
+            var read = stream.Read(buffer, offset, buffer.Length - offset);
+            if (read == 0)
+            {
+                return false;
+            }
+
+            offset += read;
+        }
+
+        return true;
+    }
+}

src/MrGameEng.Net/WebSocketServer.cs

@@ -0,0 +1,279 @@
+using System.Collections.Concurrent;
+using System.Net;
+using System.Net.Sockets;
+using MrGameEng.Core;
+
+namespace MrGameEng.Net;
+
+/// <summary>
+/// A dependency-free WebSocket server (RFC 6455 over <see cref="TcpListener"/>) for
+/// dedicated servers. Accepting and reading happen on background tasks; the simulation
+/// drains new connections with <see cref="TryAcceptConnection"/> and reads messages by
+/// polling each connection — nothing here touches the ECS world from another thread.
+/// Binary messages only; pings are answered automatically.
+/// </summary>
+public sealed class WebSocketServer : IDisposable
+{
+    /// <summary>The port the server listens on.</summary>
+    public int Port { get; }
+
+    /// <summary>Snapshot of currently open connections.</summary>
+    public IReadOnlyList<INetConnection> Connections
+    {
+        get
+        {
+            lock (_connections)
+            {
+                return _connections.Where(c => c.IsOpen).Cast<INetConnection>().ToArray();
+            }
+        }
+    }
+
+    private readonly TcpListener _listener;
+    private readonly List<ServerConnection> _connections = [];
+    private readonly ConcurrentQueue<ServerConnection> _accepted = new();
+    private readonly CancellationTokenSource _shutdown = new();
+    private int _nextConnectionId;
+    private bool _started;
+
+    /// <summary>Creates a server for <paramref name="port"/> on all interfaces. Call <see cref="Start"/> to listen.</summary>
+    public WebSocketServer(int port)
+    {
+        Port = port;
+        _listener = new TcpListener(IPAddress.Any, port);
+    }
+
+    /// <summary>Starts listening and accepting connections in the background.</summary>
+    public void Start()
+    {
+        if (_started)
+        {
+            return;
+        }
+
+        _started = true;
+        _listener.Start();
+        Task.Run(AcceptLoop);
+        Log.Info($"WebSocketServer listening on port {Port}");
+    }
+
+    /// <summary>Dequeues a connection that completed its handshake since the last call.</summary>
+    public bool TryAcceptConnection(out INetConnection connection)
+    {
+        if (_accepted.TryDequeue(out var accepted))
+        {
+            connection = accepted;
+            return true;
+        }
+
+        connection = null!;
+        return false;
+    }
+
+    /// <summary>Stops listening and closes every connection.</summary>
+    public void Dispose()
+    {
+        _shutdown.Cancel();
+        _listener.Stop();
+        lock (_connections)
+        {
+            foreach (var connection in _connections)
+            {
+                connection.Close();
+            }
+
+            _connections.Clear();
+        }
+    }
+
+    private async Task AcceptLoop()
+    {
+        while (!_shutdown.IsCancellationRequested)
+        {
+            TcpClient client;
+            try
+            {
+                client = await _listener.AcceptTcpClientAsync(_shutdown.Token);
+            }
+            catch (Exception) when (_shutdown.IsCancellationRequested)
+            {
+                return;
+            }
+            catch (Exception exception)
+            {
+                Log.Warning($"WebSocketServer accept failed: {exception.Message}");
+                continue;
+            }
+
+            _ = Task.Run(() => Handshake(client));
+        }
+    }
+
+    private void Handshake(TcpClient client)
+    {
+        try
+        {
+            client.NoDelay = true;
+            var stream = client.GetStream();
+            if (!WebSocketProtocol.TryReadHandshakeKey(stream, out var key))
+            {
+                client.Dispose();
+                return;
+            }
+
+            WebSocketProtocol.WriteHandshakeResponse(stream, key);
+            var connection = new ServerConnection(
+                Interlocked.Increment(ref _nextConnectionId),
+                client
+            );
+            lock (_connections)
+            {
+                _connections.RemoveAll(c => !c.IsOpen);
+                _connections.Add(connection);
+            }
+
+            _accepted.Enqueue(connection);
+            connection.StartReceiveLoop();
+            Log.Info($"WebSocketServer: connection #{connection.Id} accepted");
+        }
+        catch (Exception exception)
+        {
+            Log.Warning($"WebSocketServer handshake failed: {exception.Message}");
+            client.Dispose();
+        }
+    }
+
+    private sealed class ServerConnection : INetConnection
+    {
+        public int Id { get; }
+        public bool IsOpen => !_closed;
+
+        private readonly TcpClient _client;
+        private readonly NetworkStream _stream;
+        private readonly ConcurrentQueue<byte[]> _inbox = new();
+        private readonly object _sendLock = new();
+        private volatile bool _closed;
+
+        internal ServerConnection(int id, TcpClient client)
+        {
+            Id = id;
+            _client = client;
+            _stream = client.GetStream();
+        }
+
+        internal void StartReceiveLoop() => Task.Run(ReceiveLoop);
+
+        public void Send(ReadOnlySpan<byte> message)
+        {
+            if (_closed)
+            {
+                return;
+            }
+
+            var frame = WebSocketProtocol.EncodeFrame(message, WebSocketOpcode.Binary);
+            try
+            {
+                lock (_sendLock)
+                {
+                    _stream.Write(frame, 0, frame.Length);
+                }
+            }
+            catch (Exception)
+            {
+                Close();
+            }
+        }
+
+        public bool TryReceive(out byte[] message) => _inbox.TryDequeue(out message!);
+
+        public void Close()
+        {
+            if (_closed)
+            {
+                return;
+            }
+
+            _closed = true;
+            try
+            {
+                _client.Dispose();
+            }
+            catch (Exception)
+            {
+                // соединение уже мертво — закрытие не должно бросать
+            }
+        }
+
+        private void ReceiveLoop()
+        {
+            var pending = new List<byte>();
+            var pendingOpcode = WebSocketOpcode.Binary;
+            try
+            {
+                while (!_closed)
+                {
+                    if (
+                        !WebSocketProtocol.TryReadFrame(
+                            _stream,
+                            out var opcode,
+                            out var fin,
+                            out var payload
+                        )
+                    )
+                    {
+                        break;
+                    }
+
+                    switch (opcode)
+                    {
+                        case WebSocketOpcode.Ping:
+                            lock (_sendLock)
+                            {
+                                var pong = WebSocketProtocol.EncodeFrame(
+                                    payload,
+                                    WebSocketOpcode.Pong
+                                );
+                                _stream.Write(pong, 0, pong.Length);
+                            }
+
+                            continue;
+                        case WebSocketOpcode.Pong:
+                            continue;
+                        case WebSocketOpcode.Close:
+                            lock (_sendLock)
+                            {
+                                var close = WebSocketProtocol.EncodeFrame(
+                                    [],
+                                    WebSocketOpcode.Close
+                                );
+                                _stream.Write(close, 0, close.Length);
+                            }
+
+                            return;
+                    }
+
+                    if (opcode != WebSocketOpcode.Continuation)
+                    {
+                        pendingOpcode = opcode;
+                        pending.Clear();
+                    }
+
+                    pending.AddRange(payload);
+                    if (fin && pendingOpcode == WebSocketOpcode.Binary)
+                    {
+                        _inbox.Enqueue(pending.ToArray());
+                        pending.Clear();
+                    }
+                }
+            }
+            catch (Exception)
+            {
+                // обрыв соединения — штатный путь завершения цикла
+            }
+            finally
+            {
+                Close();
+            }
+        }
+    }
+}

tests/MrGameEng.Core.Tests/FormulaTests.cs

@@ -0,0 +1,112 @@
+using MrGameEng.Formulas;
+using Xunit;
+
+namespace MrGameEng.Core.Tests;
+
+public class FormulaTests
+{
+    private static IFormulaContext Vars(Dictionary<string, float> values) =>
+        new DelegateFormulaContext(name =>
+            values.TryGetValue(name, out var v)
+                ? v
+                : throw new FormulaException($"unknown '{name}'")
+        );
+
+    [Theory]
+    [InlineData("1 + 2 * 3", 7f)] // precedence
+    [InlineData("(1 + 2) * 3", 9f)] // parentheses
+    [InlineData("10 - 2 - 3", 5f)] // left associativity
+    [InlineData("-2 + 5", 3f)] // unary minus
+    [InlineData("2 * -3", -6f)] // unary minus after operator
+    [InlineData("7 % 3", 1f)] // modulo
+    [InlineData("2.5 * 4", 10f)] // decimals
+    public void Evaluate_Arithmetic_RespectsPrecedence(string expr, float expected)
+    {
+        Assert.Equal(expected, Formula.Compile(expr).Evaluate(), 4);
+    }
+
+    [Theory]
+    [InlineData("min(3, 5)", 3f)]
+    [InlineData("max(3, 5)", 5f)]
+    [InlineData("clamp(12, 0, 10)", 10f)]
+    [InlineData("clamp(-4, 0, 10)", 0f)]
+    [InlineData("lerp(0, 10, 0.25)", 2.5f)]
+    [InlineData("pow(2, 10)", 1024f)]
+    [InlineData("abs(-7)", 7f)]
+    [InlineData("floor(3.9)", 3f)]
+    [InlineData("ceil(3.1)", 4f)]
+    [InlineData("step(5, 7)", 1f)]
+    [InlineData("step(5, 2)", 0f)]
+    public void Evaluate_Functions_ComputeExpected(string expr, float expected)
+    {
+        Assert.Equal(expected, Formula.Compile(expr).Evaluate(), 4);
+    }
+
+    [Fact]
+    public void Evaluate_Constants_AreBuiltIn()
+    {
+        Assert.Equal(MathF.PI, Formula.Compile("pi").Evaluate(), 5);
+        Assert.Equal(MathF.Tau, Formula.Compile("tau").Evaluate(), 5);
+        Assert.Equal(MathF.E, Formula.Compile("e").Evaluate(), 5);
+    }
+
+    [Theory]
+    [InlineData("2 < 3", 1f)]
+    [InlineData("3 <= 3", 1f)]
+    [InlineData("3 > 5", 0f)]
+    [InlineData("4 == 4", 1f)]
+    [InlineData("4 != 4", 0f)]
+    [InlineData("1 && 0", 0f)]
+    [InlineData("0 || 2", 1f)]
+    [InlineData("!0", 1f)]
+    [InlineData("!5", 0f)]
+    public void Evaluate_LogicAndComparison_YieldBooleansAsOneOrZero(string expr, float expected)
+    {
+        Assert.Equal(expected, Formula.Compile(expr).Evaluate(), 4);
+    }
+
+    [Theory]
+    [InlineData("3 > 2 ? 10 : 20", 10f)]
+    [InlineData("3 < 2 ? 10 : 20", 20f)]
+    [InlineData("1 ? 2 ? 3 : 4 : 5", 3f)] // nested ternary
+    public void Evaluate_Ternary_SelectsBranch(string expr, float expected)
+    {
+        Assert.Equal(expected, Formula.Compile(expr).Evaluate(), 4);
+    }
+
+    [Fact]
+    public void Evaluate_Variables_ResolvedThroughContext()
+    {
+        var ctx = Vars(new() { ["light"] = 0.8f, ["optimal"] = 0.5f });
+        var formula = Formula.Compile("clamp(1 - abs(light - optimal), 0, 1)");
+        Assert.Equal(0.7f, formula.Evaluate(ctx), 4);
+    }
+
+    [Fact]
+    public void Evaluate_SameFormulaTwice_IsDeterministic()
+    {
+        var formula = Formula.Compile("sin(t) * 2 + 1");
+        var ctx = Vars(new() { ["t"] = 1.234f });
+        Assert.Equal(formula.Evaluate(ctx), formula.Evaluate(ctx), 6);
+    }
+
+    [Theory]
+    [InlineData("1 +")] // dangling operator
+    [InlineData("(1 + 2")] // unbalanced paren
+    [InlineData("1 2")] // trailing token
+    [InlineData("min(1)")] // wrong arity
+    [InlineData("nope(1)")] // unknown function
+    [InlineData("@")] // bad character
+    [InlineData("1 = 2")] // single equals
+    public void Compile_InvalidExpression_Throws(string expr)
+    {
+        Assert.Throws<FormulaException>(() => Formula.Compile(expr));
+    }
+
+    [Fact]
+    public void Evaluate_UnknownVariableWithoutContext_Throws()
+    {
+        var formula = Formula.Compile("x + 1");
+        Assert.Throws<FormulaException>(() => formula.Evaluate());
+    }
+}

tests/MrGameEng.Core.Tests/HeadlessHostTests.cs

@@ -0,0 +1,117 @@
+using MrGameEng.Core;
+using Xunit;
+
+namespace MrGameEng.Core.Tests;
+
+public class HeadlessHostTests
+{
+    private sealed class CountingScene : Scene
+    {
+        public int LoadCount;
+        public int UnloadCount;
+        public int UpdateCount;
+
+        protected override void OnLoad() => LoadCount++;
+
+        protected override void OnUnload() => UnloadCount++;
+
+        public override void Update(GameClock clock)
+        {
+            UpdateCount++;
+            base.Update(clock);
+        }
+    }
+
+    [Fact]
+    public void RunTicks_AdvancesClock_ByExactFixedStep()
+    {
+        var scene = new CountingScene();
+        using var host = new HeadlessHost(new HeadlessHostOptions { TicksPerSecond = 10f }, scene);
+
+        host.RunTicks(30);
+
+        Assert.Equal(0.1f, host.FixedDeltaTime, 3);
+        Assert.Equal(30, host.TickCount);
+        Assert.Equal(3.0, host.Context.Clock.TotalTime, 3);
+        Assert.Equal(30, scene.UpdateCount);
+    }
+
+    [Fact]
+    public void FirstTick_LoadsTheInitialScene()
+    {
+        var scene = new CountingScene();
+        using var host = new HeadlessHost(new HeadlessHostOptions(), scene);
+
+        Assert.Equal(0, scene.LoadCount);
+
+        host.Tick();
+
+        Assert.Equal(1, scene.LoadCount);
+        Assert.Same(scene, host.Context.Scenes.Current);
+    }
+
+    [Fact]
+    public void Dispose_UnloadsTheActiveScene()
+    {
+        var scene = new CountingScene();
+        var host = new HeadlessHost(new HeadlessHostOptions(), scene);
+        host.Tick();
+
+        host.Dispose();
+
+        Assert.Equal(1, scene.UnloadCount);
+        Assert.Null(host.Context.Scenes.Current);
+    }
+
+    [Fact]
+    public void Run_StopsWhenCancelled()
+    {
+        using var cancellation = new CancellationTokenSource();
+        var scene = new CancellingScene(cancellation, afterTicks: 5);
+        using var host = new HeadlessHost(new HeadlessHostOptions { Realtime = false }, scene);
+
+        host.Run(cancellation.Token);
+
+        Assert.Equal(5, scene.UpdateCount);
+    }
+
+    [Fact]
+    public void TimeScale_StillApplies_OnTopOfFixedStep()
+    {
+        var scene = new CountingScene();
+        using var host = new HeadlessHost(new HeadlessHostOptions { TicksPerSecond = 10f }, scene);
+        host.Context.Clock.TimeScale = 3f;
+
+        host.RunTicks(10);
+
+        Assert.Equal(3.0, host.Context.Clock.TotalTime, 3);
+        Assert.Equal(1.0, host.Context.Clock.UnscaledTotalTime, 3);
+    }
+
+    [Fact]
+    public void NonPositiveTickRate_Throws()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            new HeadlessHost(new HeadlessHostOptions { TicksPerSecond = 0f }, new CountingScene())
+        );
+    }
+
+    private sealed class CancellingScene(CancellationTokenSource cancellation, int afterTicks)
+        : Scene
+    {
+        public int UpdateCount;
+
+        protected override void OnLoad() { }
+
+        public override void Update(GameClock clock)
+        {
+            UpdateCount++;
+            if (UpdateCount >= afterTicks)
+            {
+                cancellation.Cancel();
+            }
+
+            base.Update(clock);
+        }
+    }
+}

tests/MrGameEng.Core.Tests/SceneTransitionTests.cs

@@ -15,6 +15,14 @@ public class SceneTransitionTests
         protected override void OnUnload() => UnloadCount++;
     }
 
+    // Тайминг-машина живёт в ядре и не зависит от визуала перехода —
+    // тестируем на голой заглушке с длительностями, как у Fade.
+    private sealed class TimedTransition(float outDuration, float inDuration)
+        : Transition(outDuration, inDuration);
+
+    private static Transition Fade(float duration) =>
+        new TimedTransition(duration / 2f, duration / 2f);
+
     private static void Tick(EngineContext context, float seconds)
     {
         context.Clock.Advance(seconds);
@@ -31,7 +39,7 @@ public class SceneTransitionTests
         Tick(context, 0.016f);
 
         // Fade(1.0) → фаза закрытия 0.5 c, фаза открытия 0.5 c.
-        context.Scenes.Switch(second, Transition.Fade(1f));
+        context.Scenes.Switch(second, Fade(1f));
         Tick(context, 0.2f);
 
         Assert.True(context.Scenes.IsTransitioning);
@@ -61,7 +69,7 @@ public class SceneTransitionTests
         Tick(context, 0.016f);
         context.Clock.TimeScale = 0f; // игра на паузе
 
-        context.Scenes.Switch(second, Transition.Fade(0.2f));
+        context.Scenes.Switch(second, Fade(0.2f));
         Tick(context, 0.15f);
         Tick(context, 0.15f);
 
@@ -79,7 +87,7 @@ public class SceneTransitionTests
         context.Scenes.Switch(first);
         Tick(context, 0.016f);
 
-        context.Scenes.Switch(second, Transition.Fade(1f));
+        context.Scenes.Switch(second, Fade(1f));
         Tick(context, 0.1f);
         context.Scenes.Switch(third); // передумали, пока экран закрывается
 
@@ -99,12 +107,12 @@ public class SceneTransitionTests
         context.Scenes.Switch(first);
         Tick(context, 0.016f);
 
-        context.Scenes.Switch(second, Transition.Fade(1f)); // 0.5 c закрытие + 0.5 c открытие
+        context.Scenes.Switch(second, Fade(1f)); // 0.5 c закрытие + 0.5 c открытие
         Tick(context, 0.6f); // закрыто, своп на second, началось открытие
         Assert.Same(second, context.Scenes.Current);
 
         Tick(context, 0.25f); // открытие наполовину (coverage ~0.5)
-        context.Scenes.Switch(third, Transition.Fade(1f)); // передумали во время открытия
+        context.Scenes.Switch(third, Fade(1f)); // передумали во время открытия
 
         Tick(context, 0.05f); // экран снова закрывается — свопа ещё нет
         Assert.Same(second, context.Scenes.Current);
@@ -124,7 +132,7 @@ public class SceneTransitionTests
         context.Scenes.Switch(first);
         Tick(context, 0.016f);
 
-        context.Scenes.Switch(second, Transition.Fade(0f));
+        context.Scenes.Switch(second, Fade(0f));
         Tick(context, 0.016f);
         Tick(context, 0.016f);
 

tests/MrGameEng.Graphics.Tests/LightmapBuilderTests.cs

@@ -0,0 +1,69 @@
+using MrGameEng.Lighting;
+using Xunit;
+
+namespace MrGameEng.Lighting.Tests;
+
+public class LightmapBuilderTests
+{
+    private static float[] Build(
+        int width,
+        int height,
+        float ambient,
+        bool[] occluders,
+        params LightSample[] lights
+    )
+    {
+        var light = new float[width * height];
+        LightmapBuilder.Build(light, width, height, ambient, occluders, lights);
+        return light;
+    }
+
+    [Fact]
+    public void Ambient_WithoutOccluders_IsUniform()
+    {
+        var light = Build(4, 4, 0.6f, new bool[16]);
+        Assert.All(light, v => Assert.Equal(0.6f, v, 5));
+    }
+
+    [Fact]
+    public void OccluderCell_IsDarkerThanOpenCell()
+    {
+        var occ = new bool[9];
+        occ[4] = true; // centre cell shaded
+        var light = Build(3, 3, 0.8f, occ);
+        Assert.True(light[4] < light[0]);
+        Assert.Equal(0.8f * LightmapBuilder.OccluderShade, light[4], 5);
+    }
+
+    [Fact]
+    public void PointLight_IsBrighterNearSourceAndFadesToRadius()
+    {
+        var light = Build(7, 1, 0f, new bool[7], new LightSample(0, 0, 6f, 1f));
+        Assert.True(light[0] > light[2] && light[2] > light[5]);
+        Assert.InRange(light[6], 0f, 0.01f); // на радиусе свет угасает
+    }
+
+    [Fact]
+    public void Occluder_CastsShadowBehindIt()
+    {
+        var occ = new bool[7];
+        occ[3] = true; // препятствие между источником (0) и дальними клетками
+        var light = Build(7, 1, 0f, occ, new LightSample(0, 0, 10f, 1f));
+
+        Assert.True(light[1] > 0f); // перед препятствием — освещено
+        Assert.Equal(0f, light[5], 5); // за препятствием — тень
+    }
+
+    [Fact]
+    public void Values_StayWithinUnitRange()
+    {
+        var light = Build(
+            5,
+            5,
+            0.5f,
+            new bool[25],
+            new LightSample(2, 2, 4f, 2f) // яркий свет — проверяем клампинг
+        );
+        Assert.All(light, v => Assert.InRange(v, 0f, 1f));
+    }
+}

tests/MrGameEng.Host.Tests/MrGameEng.Host.Tests.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <PackageReference Include="xunit.v3" />
+    <PackageReference Include="xunit.runner.visualstudio" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\MrGameEng.Host\MrGameEng.Host.csproj" />
+  </ItemGroup>
+</Project>

tests/MrGameEng.Net.Tests/MrGameEng.Net.Tests.csproj

@@ -0,0 +1,17 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <OutputType>Exe</OutputType>
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <PackageReference Include="xunit.v3" />
+    <PackageReference Include="xunit.runner.visualstudio" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\MrGameEng.Net\MrGameEng.Net.csproj" />
+  </ItemGroup>
+</Project>

tests/MrGameEng.Net.Tests/ReplicationTests.cs

@@ -0,0 +1,200 @@
+using System.Collections.Concurrent;
+using Friflo.Engine.ECS;
+using MrGameEng.Net;
+using Xunit;
+
+namespace MrGameEng.Net.Tests;
+
+public class ReplicationTests
+{
+    private struct TestPosition : IComponent
+    {
+        public float X;
+        public float Y;
+    }
+
+    private struct TestHealth : IComponent
+    {
+        public int Value;
+    }
+
+    private sealed class FakeConnection : INetConnection
+    {
+        public int Id { get; init; }
+        public bool IsOpen { get; set; } = true;
+        public readonly ConcurrentQueue<byte[]> Sent = new();
+
+        public void Send(ReadOnlySpan<byte> message) => Sent.Enqueue(message.ToArray());
+
+        public bool TryReceive(out byte[] message) => Sent.TryDequeue(out message!);
+
+        public void Close() => IsOpen = false;
+    }
+
+    private static ReplicationSchema MakeSchema() =>
+        new ReplicationSchema().Register<TestPosition>().Register<TestHealth>();
+
+    [Fact]
+    public void FirstSnapshot_SpawnsEntities_OnTheClient()
+    {
+        var serverStore = new EntityStore();
+        var clientStore = new EntityStore();
+        var server = new ReplicationServer(MakeSchema(), serverStore);
+        var client = new ReplicationClient(MakeSchema(), clientStore);
+        var connection = new FakeConnection();
+
+        serverStore.CreateEntity(
+            new NetId { Value = server.NextNetId() },
+            new TestPosition { X = 10f, Y = 20f },
+            new TestHealth { Value = 7 }
+        );
+        serverStore.CreateEntity(
+            new NetId { Value = server.NextNetId() },
+            new TestPosition { X = -3f, Y = 4f }
+        );
+
+        server.Send([connection]);
+        client.Pump(connection);
+
+        Assert.Equal(2, client.EntityCount);
+        var first = FindByNetId(clientStore, 1);
+        Assert.Equal(10f, first.GetComponent<TestPosition>().X);
+        Assert.Equal(7, first.GetComponent<TestHealth>().Value);
+        var second = FindByNetId(clientStore, 2);
+        Assert.False(second.HasComponent<TestHealth>());
+    }
+
+    [Fact]
+    public void UnchangedWorld_SendsNothing()
+    {
+        var serverStore = new EntityStore();
+        var server = new ReplicationServer(MakeSchema(), serverStore);
+        var connection = new FakeConnection();
+        serverStore.CreateEntity(
+            new NetId { Value = server.NextNetId() },
+            new TestPosition { X = 1f, Y = 1f }
+        );
+
+        server.Send([connection]);
+        Assert.Single(connection.Sent);
+
+        server.Send([connection]);
+        Assert.Single(connection.Sent); // дельта пустая — второго сообщения нет
+    }
+
+    [Fact]
+    public void ChangedComponent_IsTheOnlyThingResent()
+    {
+        var serverStore = new EntityStore();
+        var clientStore = new EntityStore();
+        var server = new ReplicationServer(MakeSchema(), serverStore);
+        var client = new ReplicationClient(MakeSchema(), clientStore);
+        var connection = new FakeConnection();
+
+        var entity = serverStore.CreateEntity(
+            new NetId { Value = server.NextNetId() },
+            new TestPosition { X = 1f, Y = 1f },
+            new TestHealth { Value = 100 }
+        );
+        server.Send([connection]);
+        client.Pump(connection);
+
+        entity.AddComponent(new TestPosition { X = 5f, Y = 6f }); // здоровье не трогаем
+        server.Send([connection]);
+
+        Assert.True(connection.Sent.TryDequeue(out var delta));
+        // Запись: type(1) + count(4) + netId(4) + op(1) + mask(4) + TestPosition(8) — без TestHealth.
+        Assert.Equal(22, delta!.Length);
+
+        client.Apply(delta);
+        var replicated = FindByNetId(clientStore, 1);
+        Assert.Equal(5f, replicated.GetComponent<TestPosition>().X);
+        Assert.Equal(100, replicated.GetComponent<TestHealth>().Value);
+    }
+
+    [Fact]
+    public void DeletedEntity_DespawnsOnTheClient()
+    {
+        var serverStore = new EntityStore();
+        var clientStore = new EntityStore();
+        var server = new ReplicationServer(MakeSchema(), serverStore);
+        var client = new ReplicationClient(MakeSchema(), clientStore);
+        var connection = new FakeConnection();
+
+        var entity = serverStore.CreateEntity(
+            new NetId { Value = server.NextNetId() },
+            new TestPosition { X = 1f, Y = 1f }
+        );
+        server.Send([connection]);
+        client.Pump(connection);
+        Assert.Equal(1, client.EntityCount);
+
+        entity.DeleteEntity();
+        server.Send([connection]);
+        client.Pump(connection);
+
+        Assert.Equal(0, client.EntityCount);
+    }
+
+    [Fact]
+    public void LateJoiner_GetsFullState()
+    {
+        var serverStore = new EntityStore();
+        var server = new ReplicationServer(MakeSchema(), serverStore);
+        var early = new FakeConnection { Id = 1 };
+        var late = new FakeConnection { Id = 2 };
+
+        serverStore.CreateEntity(
+            new NetId { Value = server.NextNetId() },
+            new TestPosition { X = 9f, Y = 9f }
+        );
+        server.Send([early]);
+        server.Send([early, late]); // мир не менялся: early — тишина, late — полный стейт
+
+        Assert.Single(early.Sent);
+        Assert.Single(late.Sent);
+
+        var clientStore = new EntityStore();
+        var client = new ReplicationClient(MakeSchema(), clientStore);
+        client.Pump(late);
+        Assert.Equal(1, client.EntityCount);
+        Assert.Equal(9f, FindByNetId(clientStore, 1).GetComponent<TestPosition>().X);
+    }
+
+    [Fact]
+    public void EntitySpawned_FiresOncePerEntity()
+    {
+        var serverStore = new EntityStore();
+        var clientStore = new EntityStore();
+        var server = new ReplicationServer(MakeSchema(), serverStore);
+        var client = new ReplicationClient(MakeSchema(), clientStore);
+        var connection = new FakeConnection();
+        var spawns = 0;
+        client.EntitySpawned += _ => spawns++;
+
+        var entity = serverStore.CreateEntity(
+            new NetId { Value = server.NextNetId() },
+            new TestPosition { X = 1f, Y = 1f }
+        );
+        server.Send([connection]);
+        client.Pump(connection);
+        entity.AddComponent(new TestPosition { X = 2f, Y = 2f });
+        server.Send([connection]);
+        client.Pump(connection);
+
+        Assert.Equal(1, spawns);
+    }
+
+    private static Entity FindByNetId(EntityStore store, int netId)
+    {
+        foreach (var entity in store.Entities)
+        {
+            if (entity.HasComponent<NetId>() && entity.GetComponent<NetId>().Value == netId)
+            {
+                return entity;
+            }
+        }
+
+        throw new InvalidOperationException($"Entity with NetId {netId} not found.");
+    }
+}

tests/MrGameEng.Net.Tests/WebSocketLoopbackTests.cs

@@ -0,0 +1,93 @@
+using System.Net;
+using System.Net.Sockets;
+using MrGameEng.Net;
+using Xunit;
+
+namespace MrGameEng.Net.Tests;
+
+public class WebSocketLoopbackTests
+{
+    [Fact]
+    public async Task ClientAndServer_ExchangeBinaryMessages_OverLoopback()
+    {
+        var port = FreePort();
+        using var server = new WebSocketServer(port);
+        server.Start();
+
+        using var client = await WebSocketClient.ConnectAsync(
+            new Uri($"ws://localhost:{port}/"),
+            new CancellationTokenSource(TimeSpan.FromSeconds(10)).Token
+        );
+
+        var connection = await WaitFor(
+            () => server.TryAcceptConnection(out var c) ? c : null,
+            "server accept"
+        );
+
+        // Сервер → клиент.
+        connection.Send([1, 2, 3, 250]);
+        var received = await WaitFor(
+            () => client.TryReceive(out var m) ? m : null,
+            "client receive"
+        );
+        Assert.Equal(new byte[] { 1, 2, 3, 250 }, received);
+
+        // Клиент → сервер (ClientWebSocket маскирует кадры — сервер обязан размаскировать).
+        client.Send([9, 8, 7]);
+        var echoed = await WaitFor(
+            () => connection.TryReceive(out var m) ? m : null,
+            "server receive"
+        );
+        Assert.Equal(new byte[] { 9, 8, 7 }, echoed);
+
+        Assert.True(connection.IsOpen);
+        Assert.True(client.IsOpen);
+    }
+
+    [Fact]
+    public async Task ClosingTheClient_ClosesTheServerConnection()
+    {
+        var port = FreePort();
+        using var server = new WebSocketServer(port);
+        server.Start();
+
+        var client = await WebSocketClient.ConnectAsync(
+            new Uri($"ws://localhost:{port}/"),
+            new CancellationTokenSource(TimeSpan.FromSeconds(10)).Token
+        );
+        var connection = await WaitFor(
+            () => server.TryAcceptConnection(out var c) ? c : null,
+            "server accept"
+        );
+
+        client.Close();
+
+        await WaitFor(() => connection.IsOpen ? null : "closed", "server-side close");
+        Assert.False(connection.IsOpen);
+    }
+
+    private static async Task<T> WaitFor<T>(Func<T?> poll, string what)
+        where T : class
+    {
+        for (var i = 0; i < 200; i++)
+        {
+            if (poll() is { } result)
+            {
+                return result;
+            }
+
+            await Task.Delay(25);
+        }
+
+        throw new TimeoutException($"Timed out waiting for {what}.");
+    }
+
+    private static int FreePort()
+    {
+        var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
+        listener.Stop();
+        return port;
+    }
+}

tests/MrGameEng.Net.Tests/WebSocketProtocolTests.cs

@@ -0,0 +1,88 @@
+using MrGameEng.Net;
+using Xunit;
+
+namespace MrGameEng.Net.Tests;
+
+public class WebSocketProtocolTests
+{
+    [Fact]
+    public void AcceptKey_MatchesRfc6455Example()
+    {
+        // Пример рукопожатия прямо из RFC 6455, раздел 1.3.
+        Assert.Equal(
+            "s3pPLMBiTxaQ9kYGzzhZRbK+xOo=",
+            WebSocketProtocol.AcceptKey("dGhlIHNhbXBsZSBub25jZQ==")
+        );
+    }
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(125)]
+    [InlineData(126)]
+    [InlineData(70_000)]
+    public void Frame_Roundtrips_Unmasked(int payloadLength)
+    {
+        var payload = MakePayload(payloadLength);
+        var frame = WebSocketProtocol.EncodeFrame(payload, WebSocketOpcode.Binary);
+
+        using var stream = new MemoryStream(frame);
+        Assert.True(
+            WebSocketProtocol.TryReadFrame(stream, out var opcode, out var fin, out var decoded)
+        );
+        Assert.Equal(WebSocketOpcode.Binary, opcode);
+        Assert.True(fin);
+        Assert.Equal(payload, decoded);
+    }
+
+    [Fact]
+    public void Frame_Roundtrips_Masked()
+    {
+        var payload = MakePayload(1000);
+        var frame = WebSocketProtocol.EncodeFrame(
+            payload,
+            WebSocketOpcode.Binary,
+            maskKey: [0x12, 0x34, 0x56, 0x78]
+        );
+
+        using var stream = new MemoryStream(frame);
+        Assert.True(WebSocketProtocol.TryReadFrame(stream, out _, out _, out var decoded));
+        Assert.Equal(payload, decoded);
+    }
+
+    [Fact]
+    public void TryReadHandshakeKey_ExtractsHeader()
+    {
+        var request =
+            "GET /chat HTTP/1.1\r\n"
+            + "Host: localhost\r\n"
+            + "Upgrade: websocket\r\n"
+            + "Connection: Upgrade\r\n"
+            + "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==\r\n"
+            + "Sec-WebSocket-Version: 13\r\n"
+            + "\r\n";
+        using var stream = new MemoryStream(System.Text.Encoding.ASCII.GetBytes(request));
+
+        Assert.True(WebSocketProtocol.TryReadHandshakeKey(stream, out var key));
+        Assert.Equal("dGhlIHNhbXBsZSBub25jZQ==", key);
+    }
+
+    [Fact]
+    public void TryReadFrame_TruncatedStream_ReturnsFalse()
+    {
+        var frame = WebSocketProtocol.EncodeFrame(MakePayload(100), WebSocketOpcode.Binary);
+        using var stream = new MemoryStream(frame, 0, frame.Length - 10);
+
+        Assert.False(WebSocketProtocol.TryReadFrame(stream, out _, out _, out _));
+    }
+
+    private static byte[] MakePayload(int length)
+    {
+        var payload = new byte[length];
+        for (var i = 0; i < length; i++)
+        {
+            payload[i] = (byte)(i * 31);
+        }
+
+        return payload;
+    }
+}