Add in-game developer console (MrGameEng.DevConsole)

Core gains a static Log (Debug/Info/Warning/Error + event); the engine
logs key events like scene switches. The console captures Log output
into a 2048-line ring buffer and executes registered commands with
input history (up/down), Tab prefix completion and scrolling
(PageUp/PageDown/End/wheel). Built-ins: help, clear, echo, timescale,
close, quit; games register their own (sample: stress/main/beep).

Console core is pure logic covered by headless tests; the Myra overlay
renders a single label rebuilt only when the Revision counter moves -
an idle or closed console costs nothing per frame. Toggled with the
backquote key; sample gameplay hotkeys are suppressed while open.

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

tests/MrGameEng.DevConsole.Tests/DevConsoleTests.cs

@@ -0,0 +1,147 @@
+using System.Text;
+using MrGameEng.Core;
+using Xunit;
+
+namespace MrGameEng.DevConsole.Tests;
+
+public class DevConsoleTests
+{
+    private static string Visible(DevConsole console, int lines = 50)
+    {
+        var sb = new StringBuilder();
+        console.BuildVisibleText(sb, lines);
+        return sb.ToString();
+    }
+
+    [Fact]
+    public void Execute_RunsRegisteredCommand_WithArguments()
+    {
+        using var console = new DevConsole();
+        string[]? received = null;
+        console.Register("test", "test command", (_, args) => received = args);
+
+        console.Execute("test one two");
+
+        Assert.NotNull(received);
+        Assert.Equal(["one", "two"], received!);
+        Assert.Contains("> test one two", Visible(console));
+    }
+
+    [Fact]
+    public void Execute_UnknownCommand_ReportsWithoutThrowing()
+    {
+        using var console = new DevConsole();
+
+        console.Execute("nosuchcommand");
+
+        Assert.Contains("unknown command 'nosuchcommand'", Visible(console));
+    }
+
+    [Fact]
+    public void Execute_HandlerException_IsCaughtAndLogged()
+    {
+        using var console = new DevConsole();
+        console.Register("boom", "throws", (_, _) => throw new InvalidOperationException("kaboom"));
+
+        console.Execute("boom");
+
+        Assert.Contains("[err] kaboom", Visible(console));
+    }
+
+    [Fact]
+    public void RingBuffer_OverflowDropsOldestLines()
+    {
+        using var console = new DevConsole(capacity: 4);
+
+        for (var i = 0; i < 10; i++)
+        {
+            console.WriteLine($"line{i}");
+        }
+
+        var visible = Visible(console);
+        Assert.DoesNotContain("line5", visible);
+        Assert.Contains("line6", visible);
+        Assert.Contains("line9", visible);
+    }
+
+    [Fact]
+    public void BuildVisibleText_RespectsWindowAndScroll()
+    {
+        using var console = new DevConsole();
+        for (var i = 0; i < 10; i++)
+        {
+            console.WriteLine($"line{i}");
+        }
+
+        var sb = new StringBuilder();
+        console.BuildVisibleText(sb, 3);
+        Assert.Equal("line7\nline8\nline9", sb.ToString());
+
+        console.Scroll(+2);
+        console.BuildVisibleText(sb, 3);
+        Assert.StartsWith("line5\nline6\nline7", sb.ToString());
+    }
+
+    [Fact]
+    public void History_NavigatesUpAndDown()
+    {
+        using var console = new DevConsole();
+        console.Register("a", "", (_, _) => { });
+        console.Execute("a 1");
+        console.Execute("a 2");
+
+        Assert.Equal("a 2", console.HistoryPrevious());
+        Assert.Equal("a 1", console.HistoryPrevious());
+        Assert.Equal("a 1", console.HistoryPrevious()); // упёрлись в начало
+        Assert.Equal("a 2", console.HistoryNext());
+        Assert.Equal("", console.HistoryNext());        // за последним — пустая строка
+    }
+
+    [Fact]
+    public void Complete_SingleMatch_CompletesWithTrailingSpace()
+    {
+        using var console = new DevConsole();
+
+        Assert.Equal("echo ", console.Complete("ec"));
+    }
+
+    [Fact]
+    public void Complete_MultipleMatches_ReturnsCommonPrefix_AndListsOptions()
+    {
+        using var console = new DevConsole();
+        console.Register("spawn", "", (_, _) => { });
+        console.Register("spawnall", "", (_, _) => { });
+
+        var completed = console.Complete("sp");
+
+        Assert.Equal("spawn", completed);
+        Assert.Contains("spawn  spawnall", Visible(console));
+    }
+
+    [Fact]
+    public void LogMessages_AreCaptured_WithLevelTags()
+    {
+        using var console = new DevConsole();
+
+        Log.Info("plain info");
+        Log.Warning("careful");
+
+        var visible = Visible(console);
+        Assert.Contains("plain info", visible);
+        Assert.Contains("[warn] careful", visible);
+    }
+
+    [Fact]
+    public void Revision_ChangesOnlyOnVisibleChanges()
+    {
+        using var console = new DevConsole();
+        var before = console.Revision;
+
+        console.WriteLine("x");
+        Assert.NotEqual(before, console.Revision);
+
+        before = console.Revision;
+        _ = Visible(console); // чтение не меняет ревизию
+        Assert.Equal(before, console.Revision);
+    }
+}