feat: ChunkStreamer dirty set with cardinal-neighbor remesh on load

VoxelEngine.Tests/Streaming/ChunkStreamerTests.cs

@@ -82,7 +82,7 @@ public class ChunkStreamerTests
     }
 
     [Fact]
-    public void Tick_PlayerMoves_LoadsNewChunksOnly()
+    public void Tick_PlayerMoves_LoadsNewChunks()
     {
         var cfg = new Configuration
         {
@@ -94,10 +94,24 @@ public class ChunkStreamerTests
         var (streamer, world, created) = CreateStreamer(cfg);
 
         streamer.Tick(new Vector3i(0, 0, 0));     // loads 9
-        int firstWave = created.Count;
-        streamer.Tick(new Vector3i(1, 0, 0));     // loads only the 3 new column to +x
 
-        Assert.Equal(firstWave + 3, created.Count);
+        // After the second tick the 3 new x=2 chunks must be ready.
+        // Cardinal-neighbor dirty-marking may also produce remesh renderers, so
+        // we assert on world state rather than an exact renderer count.
+        streamer.Tick(new Vector3i(1, 0, 0));
+
+        for (int z = -1; z <= 1; z++)
+        {
+            var newPos = new Vector3i(2, 0, z);
+            Assert.NotNull(world.GetChunk(newPos));
+            Assert.True(streamer.IsReady(newPos));
+        }
+        // x=-1 column must be unloaded
+        for (int z = -1; z <= 1; z++)
+        {
+            Assert.Null(world.GetChunk(new Vector3i(-1, 0, z)));
+            Assert.False(streamer.IsReady(new Vector3i(-1, 0, z)));
+        }
     }
 
     [Fact]
@@ -240,4 +254,67 @@ public class ChunkStreamerTests
         for (int i = 0; i < 9; i++) streamer.Tick(new Vector3i(0, 0, 0));
         Assert.True(streamer.SpawnReady);
     }
+
+    [Fact]
+    public void MarkDirty_RemeshesChunkOnNextTick()
+    {
+        var cfg = new Configuration
+        {
+            RenderDistanceHorizontal = 0,
+            RenderDistanceVertical = 0,
+            MaxGenerateJobsInFlight = 100,
+            MaxMeshUploadsPerFrame = 100,
+        };
+        var (streamer, _, created) = CreateStreamer(cfg);
+
+        streamer.Tick(new Vector3i(0, 0, 0));
+        Assert.Single(created);
+        var initialRenderer = created[0];
+
+        streamer.MarkDirty(new Vector3i(0, 0, 0));
+        streamer.Tick(new Vector3i(0, 0, 0));   // same chunk, but a remesh is queued
+
+        // Two renderers exist over the lifetime — old disposed, new live.
+        Assert.Equal(2, created.Count);
+        Assert.True(initialRenderer.Disposed);
+        Assert.False(created[1].Disposed);
+    }
+
+    [Fact]
+    public void Tick_LoadingChunk_MarksReadyCardinalNeighborsDirty()
+    {
+        var cfg = new Configuration
+        {
+            RenderDistanceHorizontal = 1,
+            RenderDistanceVertical = 0,
+            MaxGenerateJobsInFlight = 100,
+            MaxMeshUploadsPerFrame = 100,
+        };
+        var (streamer, _, created) = CreateStreamer(cfg);
+
+        streamer.Tick(new Vector3i(0, 0, 0));   // load initial 3×3
+        int firstWave = created.Count;           // 9 chunks
+
+        // Move so we load a new x=2 column. The new chunks become ready and
+        // mark their cardinal neighbors (x=1 column) dirty during Drain.
+        streamer.Tick(new Vector3i(1, 0, 0));    // dispatch + drain new loads → dirty marks set
+        streamer.Tick(new Vector3i(1, 0, 0));    // dispatch the queued remeshes → drain them
+
+        // Should have: 3 new loads + at least 3 remeshes of the x=1 column.
+        Assert.True(created.Count > firstWave + 3,
+            $"Expected remeshes beyond the 3 new loads; got {created.Count - firstWave}");
+    }
+
+    [Fact]
+    public void MarkDirty_OnUntrackedChunk_IsNoOp()
+    {
+        var cfg = new Configuration { RenderDistanceHorizontal = 0, RenderDistanceVertical = 0 };
+        var (streamer, _, created) = CreateStreamer(cfg);
+
+        streamer.MarkDirty(new Vector3i(99, 0, 99));
+        streamer.Tick(new Vector3i(0, 0, 0));
+
+        // Only the chunk in the load box was created; no spurious remesh.
+        Assert.Single(created);
+    }
 }