refactor(world): establish live entity composition seams

src/AcDream.App/World/LiveWorldOriginState.cs

@@ -0,0 +1,49 @@
+namespace AcDream.App.World;
+
+/// <summary>
+/// Session-scoped owner of the landblock origin used to translate retail
+/// full-cell coordinates into the current streamed world coordinate system.
+/// A placeholder can exist before the first authoritative player position;
+/// <see cref="IsKnown"/> distinguishes it from a server-confirmed origin.
+/// </summary>
+/// <remarks>
+/// This owner is update/render-thread confined with the rest of live world
+/// mutation. It intentionally exposes no cross-thread snapshot contract.
+/// </remarks>
+internal sealed class LiveWorldOriginState
+{
+    public int CenterX { get; private set; }
+    public int CenterY { get; private set; }
+    public bool IsKnown { get; private set; }
+
+    public void SetPlaceholder(int centerX, int centerY)
+    {
+        CenterX = centerX;
+        CenterY = centerY;
+        IsKnown = false;
+    }
+
+    public bool TryInitialize(int centerX, int centerY)
+    {
+        if (IsKnown)
+            return false;
+
+        CenterX = centerX;
+        CenterY = centerY;
+        IsKnown = true;
+        return true;
+    }
+
+    public void Recenter(int centerX, int centerY)
+    {
+        CenterX = centerX;
+        CenterY = centerY;
+    }
+
+    /// <summary>
+    /// Ends the accepted-origin lifetime while retaining the last coordinates
+    /// as the next placeholder. Consumers must gate them on
+    /// <see cref="IsKnown"/> until the next accepted player position.
+    /// </summary>
+    public void Reset() => IsKnown = false;
+}