fix(streaming): commit EnvCell landblocks atomically (#214)

Carry one complete cell payload with each streaming completion and publish visibility, physics, and render state on the render thread. Remove the obsolete post-readiness login reload that triggered a duplicate dungeon build.

Co-Authored-By: Codex <noreply@openai.com>

tests/AcDream.Core.Tests/Streaming/StreamingControllerDungeonGateTests.cs

@@ -163,6 +163,33 @@ public class StreamingControllerDungeonGateTests
         Assert.DoesNotContain(h.Loads, l => l.Kind == LandblockStreamJobKind.LoadFar);
     }
 
+    [Fact]
+    public void InitializeKnownLoginCenter_DungeonPerformsOneCollapseWithoutReloadChurn()
+    {
+        var h = Make();
+
+        h.Ctrl.InitializeKnownLoginCenter(0, 7, isSealedDungeon: true);
+        h.Ctrl.InitializeKnownLoginCenter(0, 7, isSealedDungeon: true);
+
+        Assert.Single(h.Loads);
+        Assert.Equal(Encode(0, 7), h.Loads[0].Id);
+        Assert.Equal(1, h.ClearCalls());
+    }
+
+    [Fact]
+    public void InitializeKnownLoginCenter_OutdoorWaitsForFirstCorrectlyCenteredTick()
+    {
+        var h = Make();
+
+        h.Ctrl.InitializeKnownLoginCenter(140, 4, isSealedDungeon: false);
+
+        Assert.Empty(h.Loads);
+        Assert.Equal(0, h.ClearCalls());
+
+        h.Ctrl.Tick(140, 4, insideDungeon: false);
+        Assert.Contains(h.Loads, load => load.Id == Encode(140, 4));
+    }
+
     [Fact]
     public void PreCollapse_AfterBootstrapTick_CancelsWindow_UnloadsResidentNeighbors_KeepsDungeon()
     {