refactor(net): own complete live session lifecycle

tests/AcDream.Core.Net.Tests/WorldSessionConstructionTests.cs

@@ -0,0 +1,41 @@
+using System.Net;
+
+namespace AcDream.Core.Net.Tests;
+
+public sealed class WorldSessionConstructionTests
+{
+    [Fact]
+    public void InvalidEndpointIsRejectedBeforeTransportAllocation()
+    {
+        int allocationCount = 0;
+        IWorldSessionTransport Allocate(IPEndPoint _)
+        {
+            allocationCount++;
+            return new TestTransport();
+        }
+
+        Assert.Throws<ArgumentNullException>(
+            () => new WorldSession(null!, Allocate));
+        Assert.Throws<ArgumentOutOfRangeException>(
+            () => new WorldSession(
+                new IPEndPoint(IPAddress.Loopback, ushort.MaxValue),
+                Allocate));
+
+        Assert.Equal(0, allocationCount);
+    }
+
+    private sealed class TestTransport : IWorldSessionTransport
+    {
+        public void Send(ReadOnlySpan<byte> datagram) { }
+
+        public void Send(IPEndPoint remote, ReadOnlySpan<byte> datagram) { }
+
+        public byte[]? Receive(TimeSpan timeout, out IPEndPoint? from)
+        {
+            from = null;
+            return null;
+        }
+
+        public void Dispose() { }
+    }
+}