diff --git a/src/AcDream.App/Streaming/StreamingRegion.cs b/src/AcDream.App/Streaming/StreamingRegion.cs
index 0bef84c..b28b547 100644
--- a/src/AcDream.App/Streaming/StreamingRegion.cs
+++ b/src/AcDream.App/Streaming/StreamingRegion.cs
@@ -21,10 +21,18 @@ public sealed class StreamingRegion
     private readonly HashSet<uint> _resident = new();
 
     /// <summary>
-    /// Landblock IDs (8.8 coordinate form: <c>(lbX &lt;&lt; 24) | (lbY &lt;&lt; 16) | 0xFFFE</c>)
-    /// in the current visible window. This is strictly the (2r+1)×(2r+1) set;
-    /// it does NOT include hysteresis-retained landblocks outside the window.
-    /// Use <see cref="Resident"/> to enumerate everything actually loaded.
+    /// Landblock IDs in the current visible window in the AC 8.8 coordinate
+    /// form: <c>(lbX &lt;&lt; 24) | (lbY &lt;&lt; 16) | 0xFFFF</c>. The trailing
+    /// <c>0xFFFF</c> selects the LandBlock dat (terrain heightmap); the
+    /// matching LandBlockInfo (static-object metadata) is at <c>0xFFFE</c>
+    /// on the same coordinates and is resolved internally by
+    /// <c>LandblockLoader</c>.
+    ///
+    /// <para>
+    /// This set is strictly the (2r+1)×(2r+1) window; it does NOT include
+    /// hysteresis-retained landblocks outside the window. Use
+    /// <see cref="Resident"/> to enumerate everything actually loaded.
+    /// </para>
     /// </summary>
     public IReadOnlyCollection<uint> Visible => _visible;
 
@@ -61,8 +69,17 @@ public sealed class StreamingRegion
         _resident.UnionWith(_visible);
     }
 
+    /// <summary>
+    /// Encode a landblock at (lbX, lbY) into the AC dat id form. Always uses
+    /// the <c>0xFFFF</c> terminator (LandBlock = terrain). The earlier
+    /// version of this method used <c>0xFFFE</c> by mistake — that's the
+    /// LandBlockInfo id, and asking <c>LandblockLoader.Load</c> to read a
+    /// LandBlock at the LandBlockInfo coords corrupts the dat reader's
+    /// buffer position, returning a half-populated <c>LandBlock.Height[]</c>
+    /// array which renders as wildly distorted "ball with spikes" terrain.
+    /// </summary>
     internal static uint EncodeLandblockId(int lbX, int lbY)
-        => ((uint)lbX << 24) | ((uint)lbY << 16) | 0xFFFEu;
+        => ((uint)lbX << 24) | ((uint)lbY << 16) | 0xFFFFu;
 
     /// <summary>
     /// Recompute the visible window around a new center and return the
diff --git a/tests/AcDream.Core.Tests/Streaming/StreamingRegionTests.cs b/tests/AcDream.Core.Tests/Streaming/StreamingRegionTests.cs
index d65b480..741ea2b 100644
--- a/tests/AcDream.Core.Tests/Streaming/StreamingRegionTests.cs
+++ b/tests/AcDream.Core.Tests/Streaming/StreamingRegionTests.cs
@@ -103,11 +103,17 @@ public class StreamingRegionTests
     [Fact]
     public void Constructor_SmallRadius_IDsMatchEncodingRule()
     {
-        // Verify EncodeLandblockId is correct (not swapped shifts).
-        // radius=0 at (0x12, 0x34) → exactly one entry, id = 0x1234FFFE.
+        // Verify EncodeLandblockId emits the LandBlock terminator (0xFFFF),
+        // not the LandBlockInfo terminator (0xFFFE). The earlier version of
+        // this test pinned 0xFFFE and codified the bug that produced "ball
+        // of spikes" terrain in Phase A.1's first live run — LandblockLoader
+        // was being asked to read the LandBlockInfo file as a LandBlock,
+        // which corrupted the dat reader's buffer position and returned a
+        // half-populated heightmap. radius=0 at (0x12, 0x34) → exactly one
+        // entry, id = 0x1234FFFF.
         var region = new StreamingRegion(cx: 0x12, cy: 0x34, radius: 0);
 
         Assert.Single(region.Visible);
-        Assert.Contains(0x1234FFFEu, region.Visible);
+        Assert.Contains(0x1234FFFFu, region.Visible);
     }
 }