chore(container-loader): tighten snapshot refresh config flag gating

packages/loader/container-loader/src/snapshotRefresher.ts

@@ -97,8 +97,7 @@ export class SnapshotRefresher implements IDisposable {
 
 		this.#snapshotRefreshEnabled =
 			this.offlineLoadEnabled &&
-			(this.mc.config.getBoolean("Fluid.Container.enableOfflineSnapshotRefresh") ??
-				this.mc.config.getBoolean("Fluid.Container.enableOfflineFull")) === true;
+			(this.mc.config.getBoolean("Fluid.Container.enableOfflineSnapshotRefresh") ?? false);
 
 		this.refreshTimer = this.#snapshotRefreshEnabled
 			? new Timer(this.snapshotRefreshTimeoutMs, () => this.tryRefreshSnapshot())

packages/loader/container-loader/src/test/snapshotRefresher.spec.ts

@@ -60,6 +60,12 @@ function enableOfflineSnapshotRefresh(logger: ITelemetryBaseLogger): ITelemetryB
 	}).logger;
 }
 
+function enableOfflineFullOnly(logger: ITelemetryBaseLogger): ITelemetryBaseLogger {
+	return mixinMonitoringContext(logger, {
+		getRawConfig: (name) => (name === "Fluid.Container.enableOfflineFull" ? true : undefined),
+	}).logger;
+}
+
 class MockStorageAdapter implements ISerializedStateManagerDocumentStorageService {
 	public readonly blobs = new Map<string, ArrayBuffer>();
 	private snapshot: ISnapshotTree;
@@ -329,6 +335,23 @@ describe("SnapshotRefresher", () => {
 
 			refresher.dispose();
 		});
+
+		it("should not trigger refresh when only enableOfflineFull is set", () => {
+			const logger = enableOfflineFullOnly(mockLogger);
+			const timeout = 1000;
+			const refresher = createRefresher(true, () => true, timeout, logger);
+
+			refresher.startTimer();
+			clock.tick(timeout);
+
+			assert.strictEqual(
+				mockStorage.getVersionsCallCount,
+				0,
+				"getVersions should not be called when only enableOfflineFull is set (enableOfflineSnapshotRefresh must be opted in explicitly)",
+			);
+
+			refresher.dispose();
+		});
 	});
 
 	describe("tryRefreshSnapshot", () => {