refactor(world): establish live entity composition seams

tests/AcDream.App.Tests/World/LiveWorldOriginStateTests.cs

@@ -0,0 +1,62 @@
+using AcDream.App.World;
+
+namespace AcDream.App.Tests.World;
+
+public sealed class LiveWorldOriginStateTests
+{
+    [Fact]
+    public void Placeholder_IsNotAuthoritativeUntilFirstInitialization()
+    {
+        var state = new LiveWorldOriginState();
+
+        state.SetPlaceholder(42, 43);
+
+        Assert.Equal(42, state.CenterX);
+        Assert.Equal(43, state.CenterY);
+        Assert.False(state.IsKnown);
+        Assert.True(state.TryInitialize(10, 11));
+        Assert.Equal(10, state.CenterX);
+        Assert.Equal(11, state.CenterY);
+        Assert.True(state.IsKnown);
+        Assert.False(state.TryInitialize(20, 21));
+        Assert.Equal(10, state.CenterX);
+        Assert.Equal(11, state.CenterY);
+    }
+
+    [Fact]
+    public void Recenter_ReplacesKnownOriginAndResetRetainsItAsPlaceholder()
+    {
+        var state = new LiveWorldOriginState();
+        Assert.True(state.TryInitialize(1, 2));
+
+        state.Recenter(3, 4);
+        state.Reset();
+
+        Assert.Equal(3, state.CenterX);
+        Assert.Equal(4, state.CenterY);
+        Assert.False(state.IsKnown);
+        Assert.True(state.TryInitialize(5, 6));
+    }
+
+    [Fact]
+    public void RecenterBeforeInitialization_PreservesUnknownAndResetIsIdempotent()
+    {
+        var state = new LiveWorldOriginState();
+        state.SetPlaceholder(20, 21);
+
+        state.Recenter(30, 31);
+        state.Reset();
+        state.Reset();
+
+        Assert.Equal(30, state.CenterX);
+        Assert.Equal(31, state.CenterY);
+        Assert.False(state.IsKnown);
+
+        Assert.True(state.TryInitialize(40, 41));
+        state.Recenter(50, 51);
+
+        Assert.True(state.IsKnown);
+        Assert.Equal(50, state.CenterX);
+        Assert.Equal(51, state.CenterY);
+    }
+}