Land fixes: ported conditional-commit pins state C2a's identity, not main's (storedAt, message text)

A staged write mints a later storedAt, so the 'rewrite kept storedAt' premise is gone; the pin is that a record rewritten under another schema fails Expect. The variant refusal names the renamed base through ChangedKeys, as C2a's typed exception carries it.

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

tests/GameCult.Caching.Tests/ConditionalCommitTests.cs

@@ -83,21 +83,18 @@ namespace GameCult.Caching.Tests
         }
 
         [Test]
-        public void RecordRewrittenUnderAnotherSchemaWithItsStoredAtFailsExpect()
+        public void RecordRewrittenUnderAnotherSchemaFailsExpect()
         {
             SeedDrift(directory: false);
             using var cache = Drift(false, NarrowDrift).Open();
             var observed = cache.Get(DriftKey)!;
-            var storedAt = cache.GetStored(DriftKey)!.StoredAt;
             using (var other = Drift(false, ReusedDrift).Open())
             {
                 other.BackingStores[0].Push(other.GetStored(DriftKey)!);
                 other.BackingStores[0].PushAll();
             }
-            using (var reader = Drift(false, ReusedDrift).Open())
-                Assert.That(reader.GetStored(DriftKey)!.StoredAt, Is.EqualTo(storedAt), "the rewrite kept storedAt");
 
-            Assert.That(DriftCommit(cache, observed, 2), Is.False, "a record rewritten under another schema passed Expect on storedAt alone");
+            Assert.That(DriftCommit(cache, observed, 2), Is.False, "a record rewritten under another schema passed Expect");
         }
 
         // The directory store rewrites only what is pushed to it, so the other writer pushes the record it read unchanged.

tests/GameCult.Caching.Tests/VariantTests.cs

@@ -1265,7 +1265,8 @@ namespace GameCult.Caching.Tests
                         a.Override<VariantGear>(nameof(VariantGear.Code), "big")
                     });
                 }))!;
-                Assert.That(refused.Message, Does.Contain(BigKey.Value).And.Contain(BaseKey.Value).And.Contain("x"));
+                Assert.That(refused.Message, Does.Contain(BigKey.Value));
+                Assert.That(refused.ChangedKeys, Is.EqualTo(new[] { BaseKey.Value }), "the refusal names the base another writer renamed");
             }
 
             using var reopened = Open(path, readOnly: true);