M3: real 3D translate gizmo — the "полноценный 3D-пайплайн" it was chosen for

TranslateGizmo draws three axis handles at the selected GameObject's
world position by projecting real 3D points through the real camera's
View/Projection (GizmoMath.WorldToScreen) onto ImGui's foreground draw
list. Nothing OpenGL-side draws lines yet, so this isn't 3D geometry
in the GL sense — but it IS driven by the actual camera matrices, which
is what the earlier scoped-2D-vs-full-3D-pipeline choice was actually
about: a handle dragged in screen space has to map onto a real 3D axis,
and that only means something once there's a real camera to project
through. The screenshot below shows exactly that — the axes aren't
screen-perpendicular, because the camera at (0,3,6) looking at the
origin means they shouldn't be.

Dragging a handle re-projects the mouse delta onto the axis's own
screen-space direction (GizmoMath.ProjectDragOntoAxis) and writes the
result back through GizmoMath.WorldToLocalPosition, which inverts the
parent's WorldMatrix rather than writing LocalPosition directly — a
parent with non-identity scale or rotation means "move 1 world unit"
and "add 1 to LocalPosition" are different amounts, and
samples/WindowDemo's ChildQuad (parented under a (2,2,1)-scaled Quad)
is exactly that case.

Split the actual math into GizmoMath (Engine.Editor.Contracts, no GL/
ImGui/mouse dependency) so it's unit-testable without a window or a real
mouse — neither exists in a headless test run, and dragging is exactly
the kind of interaction that's easy to get subtly wrong (screen-space
ratio direction, perspective sign, parent-scale correctness) without
something to check it against beyond eyeballing a screenshot. New
Engine.Editor.Tests project, 8 tests: screen-center projection, a
behind-camera point returning null, drag-ratio math on both an
axis-aligned and a diagonal screen direction, and the parent-scale/
parent-translation inverse-transform cases. All 8 passed on the first
run — including the non-uniform-scale case, the one most likely to be
subtly wrong.

Full suite: 73 tests, all green (65 previous + 8 new).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N1qPfzq8TDCUMFMV3UwV5N

plugins/engine.editor/Engine.Editor/EditorPlugin.cs

@@ -4,6 +4,7 @@ using Engine.Kernel.Diagnostics;
 using Engine.Kernel.Plugins;
 using Engine.Kernel.Scheduling;
 using Engine.Kernel.World;
+using Engine.Render.Contracts;
 using Engine.Windowing.Contracts;
 using ImGuiNET;
 using Silk.NET.OpenGL;
@@ -29,16 +30,21 @@ namespace Engine.Editor;
 public sealed class EditorPlugin : IPlugin
 {
     private readonly EditorState _state = new();
+    private readonly TranslateGizmo _gizmo = new();
     private GL? _gl;
     private ImGuiController? _controller;
     private ITime? _time;
     private PlayModeController? _playMode;
+    private IEngineWindow? _window;
+    private ICameraService? _camera;
 
     public void Configure(IPluginContext ctx)
     {
         var window = ctx.Services.Require<IEngineWindow>();
         var input = ctx.Services.Require<IEngineInput>();
         _time = ctx.Time;
+        _window = window;
+        _camera = ctx.Services.Require<ICameraService>();
 
         window.Native.GLContext!.MakeCurrent();
         _gl = window.Native.CreateOpenGL();
@@ -61,6 +67,8 @@ public sealed class EditorPlugin : IPlugin
         _gl = null;
         _time = null;
         _playMode = null;
+        _window = null;
+        _camera = null;
     }
 
     private void DrawUi(IWorld world)
@@ -101,6 +109,7 @@ public sealed class EditorPlugin : IPlugin
 
         HierarchyPanel.Draw(world, _state);
         InspectorPanel.Draw(_state);
+        _gizmo.Draw(_state, _camera!, _window!);
 
         _controller.Render();
     }