diff --git a/src/GameCult.Caching.MessagePack/CultDocumentMessagePackSerialization.cs b/src/GameCult.Caching.MessagePack/CultDocumentMessagePackSerialization.cs
index 823c82f2..90fb7c94 100644
--- a/src/GameCult.Caching.MessagePack/CultDocumentMessagePackSerialization.cs
+++ b/src/GameCult.Caching.MessagePack/CultDocumentMessagePackSerialization.cs
@@ -198,6 +198,9 @@ public static class CultDocumentMessagePackSerialization
 
         if (fieldCount > 0)
         {
+            // A stamp encoded as binary is not one this runtime wrote or reads; it is refused here, not parsed as damage.
+            if (reader.NextMessagePackType == MessagePackType.Binary)
+                throw new NotSupportedException("Store snapshot declares its format version as binary; this runtime reads " + CultPersistedStoreSnapshot.FormatV1 + " and " + CultPersistedStoreSnapshot.FormatV2 + " as strings.");
             snapshot.FormatVersion = reader.ReadString()
                 ?? throw new NotSupportedException("Store snapshot declares no format version; this runtime reads " + CultPersistedStoreSnapshot.FormatV1 + " and " + CultPersistedStoreSnapshot.FormatV2 + ".");
             requireReadable(snapshot.FormatVersion);
diff --git a/tests/GameCult.Caching.Tests/BackingStoreTests.cs b/tests/GameCult.Caching.Tests/BackingStoreTests.cs
index 7e88c283..543261ff 100644
--- a/tests/GameCult.Caching.Tests/BackingStoreTests.cs
+++ b/tests/GameCult.Caching.Tests/BackingStoreTests.cs
@@ -428,7 +428,7 @@ namespace GameCult.Caching.Tests
                     await seed.FlushAsync();
                 }
 
-                var manifest = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(filePath));
+                var manifest = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(filePath), _ => { });
                 Assert.That(manifest.FormatVersion, Is.EqualTo("cultcache.store.v4.directory-content-addressed-pages"));
                 Assert.That(manifest.Records, Has.Length.EqualTo(2));
                 Assert.That(manifest.Records.All(record => record.Payload.Length == 32), Is.True,
@@ -730,7 +730,7 @@ namespace GameCult.Caching.Tests
                 }
 
                 Assert.That(store.IsDirty, Is.False);
-                var compacted = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(filePath));
+                var compacted = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(filePath), _ => { });
                 Assert.That(compacted.SchemaCatalog, Is.Empty);
                 Assert.That(compacted.Records, Is.Empty);
                 var reader = new CultCache();
diff --git a/tests/GameCult.Caching.Tests/DirectoryStoreDurabilityTests.cs b/tests/GameCult.Caching.Tests/DirectoryStoreDurabilityTests.cs
index 840110bc..972648f5 100644
--- a/tests/GameCult.Caching.Tests/DirectoryStoreDurabilityTests.cs
+++ b/tests/GameCult.Caching.Tests/DirectoryStoreDurabilityTests.cs
@@ -223,7 +223,7 @@ namespace GameCult.Caching.Tests
         }
 
         private CultPersistedRecord ManifestRecord(CultRecordKey key) =>
-            CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(_manifest)).Records.Single(record => record.Key == key.Value);
+            CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(_manifest), _ => { }).Records.Single(record => record.Key == key.Value);
 
         private string PagePath(byte[] identity) =>
             Path.Combine(_records, BitConverter.ToString(identity).Replace("-", string.Empty).ToLowerInvariant() + ".msgpack");
diff --git a/tests/GameCult.Caching.Tests/PreCut2StoreFormatTests.cs b/tests/GameCult.Caching.Tests/PreCut2StoreFormatTests.cs
index 7e339945..7f40f913 100644
--- a/tests/GameCult.Caching.Tests/PreCut2StoreFormatTests.cs
+++ b/tests/GameCult.Caching.Tests/PreCut2StoreFormatTests.cs
@@ -47,7 +47,7 @@ namespace GameCult.Caching.Tests
             try
             {
                 var manifest = Path.Combine(root, "store.cc");
-                Assert.That(CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(manifest)).FormatVersion,
+                Assert.That(CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(manifest), _ => { }).FormatVersion,
                     Is.EqualTo("cultcache.store.v4.directory-content-addressed-pages"));
 
                 using var cache = new CultCache();
@@ -342,16 +342,6 @@ namespace GameCult.Caching.Tests
                 CultDocumentMessagePackSerialization.DeserializeUntyped(documentType, payload, Registry);
         }
 
-        private sealed class FlakyReadStore : SingleFileMessagePackBackingStore
-        {
-            public Exception? FailReadWith;
-
-            public FlakyReadStore(string path) : base(path) { }
-
-            protected override CultPersistedStoreSnapshot DeserializeSnapshot(byte[] data) =>
-                FailReadWith != null ? throw FailReadWith : base.DeserializeSnapshot(data);
-        }
-
         private static void StampHeader(string file, string header)
         {
             var snapshot = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(file));
@@ -431,15 +421,16 @@ namespace GameCult.Caching.Tests
             try
             {
                 var file = Path.Combine(root, "store.msgpack");
-                var store = new FlakyReadStore(file);
                 using var cache = new CultCache();
-                cache.AddBackingStore(store);
+                cache.AddBackingStore(new SingleFileMessagePackBackingStore(file));
                 await cache.PullAllBackingStoresAsync();
                 var before = File.ReadAllBytes(file);
 
                 await cache.AddAsync(new PreCut2FixtureNote { Text = "staged" });
-                store.FailReadWith = new IOException("transient");
-                Assert.Throws<IOException>(() => cache.FlushAllBackingStores());
+                using (new FileStream(file, FileMode.Open, FileAccess.ReadWrite, FileShare.None))
+                {
+                    Assert.Throws<IOException>(() => cache.FlushAllBackingStores());
+                }
                 Assert.That(File.ReadAllBytes(file), Is.EqualTo(before));
             }
             finally
@@ -460,7 +451,7 @@ namespace GameCult.Caching.Tests
                 cache.AddBackingStore(new DirectoryMessagePackBackingStore(manifest));
                 await cache.PullAllBackingStoresAsync();
 
-                var snapshot = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(manifest));
+                var snapshot = CultDocumentMessagePackSerialization.DeserializeSnapshot(File.ReadAllBytes(manifest), _ => { });
                 snapshot.FormatVersion = newer;
                 File.WriteAllBytes(manifest, CultDocumentMessagePackSerialization.SerializeSnapshot(snapshot));
                 Func<System.Collections.Generic.Dictionary<string, byte[]>> files = () => Directory