G1: bump engine (formula engine + Host split), wire formula demo

Engine pointer -> 10898b0, which brings in two engine changes:
- the gene-system formula engine (Core): a data-driven expression
  evaluator that compiles a def string once and evaluates it
  allocation-free against a variable context;
- a parallel refactor splitting the platform out of Core into a new
  MrGameEng.Host library.

Game migration for the Host split: reference MrGameEng.Host (+ add it
and its test project to the solution), import MrGameEng.Host where
GameHost/GameHostOptions/Input are used, switch Transition.Fade ->
Transitions.Fade, and read the device via context.GetGraphicsDevice()
now that EngineContext is platform-free.

Showcase the formula engine with a dev-console 'formula <expr>' command
that compiles and evaluates an expression. Also adds docs/гены.md, the
gene-system design doc (phases G1-G5).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/LittleSim/LittleSim.csproj

@@ -6,6 +6,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\engine\src\MrGameEng.Core\MrGameEng.Core.csproj" />
+    <ProjectReference Include="..\..\engine\src\MrGameEng.Host\MrGameEng.Host.csproj" />
     <ProjectReference Include="..\..\engine\src\MrGameEng.Graphics\MrGameEng.Graphics.csproj" />
     <ProjectReference Include="..\..\engine\src\MrGameEng.Audio\MrGameEng.Audio.csproj" />
     <ProjectReference Include="..\..\engine\src\MrGameEng.Content\MrGameEng.Content.csproj" />

src/LittleSim/Program.cs

@@ -1,6 +1,7 @@
 using LittleSim.Scenes;
 using Microsoft.Xna.Framework;
 using MrGameEng.Core;
+using MrGameEng.Host;
 
 // Контент Core-мода грузится уже в окне — на загрузочном экране (BootScene), в фоне.
 using var host = new GameHost(

src/LittleSim/Scenes/BootScene.cs

@@ -5,6 +5,7 @@ using LittleSim.UI;
 using Microsoft.Xna.Framework;
 using MrGameEng.Audio;
 using MrGameEng.Core;
+using MrGameEng.Host;
 using MrGameEng.UI;
 using Myra.Graphics2D.UI;
 
@@ -73,6 +74,6 @@ public sealed class BootScene : Scene
         Context.Services.Add(content);
         Context.Services.Add(new ModAtlases(content.AtlasCacheDirectory));
         content.Languages.SetLanguage(_settings.Language);
-        Context.Scenes.Switch(new MainMenuScene(), Transition.Fade(0.6f));
+        Context.Scenes.Switch(new MainMenuScene(), Transitions.Fade(0.6f));
     }
 }

src/LittleSim/Scenes/CreditsScene.cs

@@ -2,6 +2,7 @@ using LittleSim.Content;
 using LittleSim.UI;
 using Microsoft.Xna.Framework.Input;
 using MrGameEng.Core;
+using MrGameEng.Host;
 using MrGameEng.Input;
 using MrGameEng.UI;
 
@@ -40,7 +41,7 @@ public sealed class CreditsScene : Scene
     {
         if (!Context.Scenes.IsTransitioning)
         {
-            Context.Scenes.Switch(new MainMenuScene(), Transition.Fade(0.4f));
+            Context.Scenes.Switch(new MainMenuScene(), Transitions.Fade(0.4f));
         }
     }
 }

src/LittleSim/Scenes/LoadGameScene.cs

@@ -3,6 +3,7 @@ using LittleSim.Content;
 using LittleSim.UI;
 using Microsoft.Xna.Framework.Input;
 using MrGameEng.Core;
+using MrGameEng.Host;
 using MrGameEng.Input;
 using MrGameEng.UI;
 using Myra.Graphics2D.UI;
@@ -73,7 +74,7 @@ public sealed class LoadGameScene : Scene
                         {
                             Context.Scenes.Switch(
                                 new WorldScene(save.ToConfig(), save),
-                                Transition.Fade(0.6f)
+                                Transitions.Fade(0.6f)
                             );
                         }
                     },
@@ -104,7 +105,7 @@ public sealed class LoadGameScene : Scene
     {
         if (!Context.Scenes.IsTransitioning)
         {
-            Context.Scenes.Switch(new MainMenuScene(), Transition.Fade(0.4f));
+            Context.Scenes.Switch(new MainMenuScene(), Transitions.Fade(0.4f));
         }
     }
 }

src/LittleSim/Scenes/MainMenuScene.cs

@@ -2,6 +2,7 @@ using LittleSim.Content;
 using LittleSim.UI;
 using Microsoft.Xna.Framework;
 using MrGameEng.Core;
+using MrGameEng.Host;
 using MrGameEng.UI;
 
 namespace LittleSim.Scenes;
@@ -37,7 +38,7 @@ public sealed class MainMenuScene : Scene
     {
         if (!Context.Scenes.IsTransitioning)
         {
-            Context.Scenes.Switch(scene, Transition.Fade(0.4f));
+            Context.Scenes.Switch(scene, Transitions.Fade(0.4f));
         }
     }
 }

src/LittleSim/Scenes/NewWorldScene.cs

@@ -6,6 +6,7 @@ using LittleSim.Content;
 using LittleSim.UI;
 using Microsoft.Xna.Framework.Input;
 using MrGameEng.Core;
+using MrGameEng.Host;
 using MrGameEng.Input;
 using MrGameEng.UI;
 using Myra.Graphics2D.UI;
@@ -153,14 +154,14 @@ public sealed class NewWorldScene : Scene
             Seed = seed,
             SmoothPasses = _smoothing,
         };
-        Context.Scenes.Switch(new WorldScene(config), Transition.Fade(0.6f));
+        Context.Scenes.Switch(new WorldScene(config), Transitions.Fade(0.6f));
     }
 
     private void Back()
     {
         if (!Context.Scenes.IsTransitioning)
         {
-            Context.Scenes.Switch(new MainMenuScene(), Transition.Fade(0.4f));
+            Context.Scenes.Switch(new MainMenuScene(), Transitions.Fade(0.4f));
         }
     }
 }

src/LittleSim/Scenes/PauseMenu.cs

@@ -5,6 +5,7 @@ using LittleSim.UI;
 using Microsoft.Xna.Framework;
 using MrGameEng.Audio;
 using MrGameEng.Core;
+using MrGameEng.Host;
 using Myra.Graphics2D.Brushes;
 using Myra.Graphics2D.UI;
 

src/LittleSim/Scenes/SettingsScene.cs

@@ -5,6 +5,7 @@ using Microsoft.Xna.Framework;
 using Microsoft.Xna.Framework.Input;
 using MrGameEng.Audio;
 using MrGameEng.Core;
+using MrGameEng.Host;
 using MrGameEng.Input;
 using MrGameEng.UI;
 using Myra.Graphics2D.UI;
@@ -59,7 +60,7 @@ public sealed class SettingsScene : Scene
     {
         if (!Context.Scenes.IsTransitioning)
         {
-            Context.Scenes.Switch(new MainMenuScene(), Transition.Fade(0.4f));
+            Context.Scenes.Switch(new MainMenuScene(), Transitions.Fade(0.4f));
         }
     }
 }

src/LittleSim/Scenes/WorldScene.cs

@@ -10,7 +10,9 @@ using Microsoft.Xna.Framework.Input;
 using MrGameEng.Assets;
 using MrGameEng.Core;
 using MrGameEng.DevConsole;
+using MrGameEng.Formulas;
 using MrGameEng.Graphics;
+using MrGameEng.Host;
 using MrGameEng.Input;
 using MrGameEng.Inspector;
 using MrGameEng.Lighting;
@@ -73,7 +75,7 @@ public sealed class WorldScene : Scene
         var assets = Context.Services.GetOrDefault<AssetManager>() ?? Context.UseAssets();
         var content = Context.Services.Get<GameContent>();
         var atlases = Context.Services.Get<ModAtlases>();
-        var device = Context.GraphicsDevice;
+        var device = Context.GetGraphicsDevice();
         var input = this.UseInput();
         _speed = Context.Services.Get<GameSpeed>();
         _speed.SetStep(0); // новый мир/загрузка стартуют на x1
@@ -435,7 +437,7 @@ public sealed class WorldScene : Scene
         if (!Context.Scenes.IsTransitioning)
         {
             _speed.Resume();
-            Context.Scenes.Switch(scene, Transition.Fade(0.5f));
+            Context.Scenes.Switch(scene, Transitions.Fade(0.5f));
         }
     }
 
@@ -456,10 +458,34 @@ public sealed class WorldScene : Scene
                 c.WriteLine($"regenerating world, seed {seed}");
                 Context.Scenes.Switch(
                     new WorldScene(_config with { Seed = seed }),
-                    Transition.Fade(0.6f)
+                    Transitions.Fade(0.6f)
                 );
             }
         );
+        console.Register(
+            "formula",
+            "formula <expr> — compile and evaluate an expression (gene-formula engine demo)",
+            (c, args) =>
+            {
+                if (args.Length == 0)
+                {
+                    c.WriteLine(
+                        "usage: formula <expr>  e.g. formula clamp(lerp(0, 10, 0.5), 0, 8)"
+                    );
+                    return;
+                }
+
+                var expression = string.Join(' ', args);
+                try
+                {
+                    c.WriteLine($"{expression} = {Formula.Compile(expression).Evaluate()}");
+                }
+                catch (FormulaException e)
+                {
+                    c.WriteLine($"error: {e.Message}");
+                }
+            }
+        );
         console.Register(
             "menu",
             "menu — return to the main menu",