Networking tests: pin the write-side depth check on ToRawRecord with no binding

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/GameCult.Networking.Tests/BytesAfterPathTests.cs

@@ -21,7 +21,15 @@ namespace GameCult.Networking.Tests
             [Key(1)] public int N = 3;
         }
 
-        private static readonly CultDocumentRegistry Documents = CultDocumentRegistry.ForTypes(new[] { typeof(TailDoc) });
+        [CultDocument("tests.bytes_after_deep", "tests.bytes_after_deep.v1")]
+        [MessagePackObject]
+        public sealed class DeepDoc
+        {
+            [Key(0)] [CultName] public string Id = "a";
+            [Key(1)] public DeepDoc Inner;
+        }
+
+        private static readonly CultDocumentRegistry Documents = CultDocumentRegistry.ForTypes(new[] { typeof(TailDoc), typeof(DeepDoc) });
 
         private static byte[] WithTail() =>
             CultDocumentMessagePackSerialization.SerializeUntyped(new TailDoc(), typeof(TailDoc), Documents).Concat(new byte[] { 0xc0 }).ToArray();
@@ -58,5 +66,28 @@ namespace GameCult.Networking.Tests
             var registry = new CultNetDocumentRegistry(Documents);
             Refuses(() => registry.DeserializeRawDocument(Raw(registry, WithTail())));
         }
+
+        // The write side of the same rule: a record with no binding is serialized by SerializeUntyped, and a payload nested past
+        // the limit is refused there, before it can reach the wire.
+        [Test]
+        public void ToRawRecordWithNoBindingRefusesAPayloadNestedPastTheLimit()
+        {
+            var registry = new CultNetDocumentRegistry(Documents);
+            var descriptor = Documents.GetRequired(typeof(DeepDoc));
+            DeepDoc Chain(int links)
+            {
+                var head = new DeepDoc();
+                var tip = head;
+                for (var i = 0; i < links; i++) tip = tip.Inner = new DeepDoc();
+                return head;
+            }
+
+            // Each link is one array; the root is depth 1, so 255 links is depth 256 (at the limit) and 256 links is 257.
+            Assert.That(registry.ToRawRecord(descriptor, new CultRecordKey("a"), Chain(255), "1970-01-01T00:00:00.000Z").Payload, Is.Not.Empty);
+            var refused = Assert.Throws<MessagePackSerializationException>(
+                () => registry.ToRawRecord(descriptor, new CultRecordKey("a"), Chain(256), "1970-01-01T00:00:00.000Z"))!;
+            Assert.That(refused.Message, Does.Contain("refused on write"));
+            Assert.That(refused.Message, Does.Contain(typeof(DeepDoc).FullName));
+        }
     }
 }