step 4

tests/PersistenceWriterTests.cpp

@@ -94,12 +94,42 @@ void TestImmediateRequestsAreNotCoalesced()
 			"immediate snapshots preserve order");
 	}
 }
+
+void TestWriteFailureReportsStructuredResult()
+{
+	std::vector<PersistenceWriteResult> results;
+	PersistenceWriter writer(
+		std::chrono::milliseconds(1),
+		[](const PersistenceSnapshot&, std::string& error) {
+			error = "simulated failure";
+			return false;
+		});
+	writer.SetResultCallback([&results](const PersistenceWriteResult& result) {
+		results.push_back(result);
+	});
+
+	PersistenceSnapshot snapshot = MakeRuntimeSnapshot("payload");
+	snapshot.debounceAllowed = false;
+	snapshot.reason = "failure-test";
+
+	std::string error;
+	Expect(writer.EnqueueSnapshot(snapshot, error), "failing snapshot still enqueues");
+	writer.StopAndFlush();
+
+	Expect(results.size() == 1, "writer reports one failure result");
+	Expect(!results.empty() && !results[0].succeeded, "writer result records failure");
+	Expect(!results.empty() && results[0].reason == "failure-test", "writer result preserves reason");
+	Expect(!results.empty() && results[0].errorMessage == "simulated failure", "writer result preserves error message");
+	Expect(!results.empty() && !results[0].newerRequestPending, "writer result reports no newer pending request");
+	Expect(writer.GetMetrics().failedCount == 1, "writer metrics count failed writes");
+}
 }
 
 int main()
 {
 	TestDebouncedRequestsCoalesceToNewestSnapshot();
 	TestImmediateRequestsAreNotCoalesced();
+	TestWriteFailureReportsStructuredResult();
 
 	if (gFailures != 0)
 	{