feat(content): bake and read flat collision assets

Append strict collision/topology payloads to the existing prepared package so later physics cutover can drop parsed DAT graphs without adding a second mapping or changing traversal behavior. The full 2,232,170-key catalog is deterministic across worker counts, exact-byte aliased, corruption-isolated, and cancellation-safe.

tests/AcDream.Bake.Tests/BakeOutputTransactionTests.cs

@@ -154,6 +154,33 @@ public sealed class BakeOutputTransactionTests : IDisposable
             () => BakeArtifactValidator.Validate(pak, expected, expectedTocCount: 1));
     }
 
+    [Fact]
+    public void ArtifactValidator_RejectsIncompleteTypedCatalog()
+    {
+        string pak = Path.Combine(_directory, "typed-content.pak");
+        var expected = Header();
+        using (var writer = new PakWriter(pak, expected))
+        {
+            writer.AddBlob(
+                PakKey.Compose(PakAssetType.GfxObjMesh, 1),
+                new ObjectMeshData { ObjectId = 1 });
+            writer.Finish();
+        }
+
+        var expectedTypes = new Dictionary<PakAssetType, int>
+        {
+            [PakAssetType.GfxObjMesh] = 1,
+            [PakAssetType.GfxObjCollision] = 1,
+        };
+        InvalidDataException exception = Assert.Throws<InvalidDataException>(
+            () => BakeArtifactValidator.Validate(
+                pak,
+                expected,
+                expectedTocCount: 1,
+                expectedTypeCounts: expectedTypes));
+        Assert.Contains("GfxObjCollision", exception.Message);
+    }
+
     private PakHeader Header() =>
         new()
         {