fix(csharp): disable feature flag cache by default

csharp/src/DatabricksParameters.cs

@@ -360,7 +360,7 @@ public class DatabricksParameters : SparkParameters
         /// <summary>
         /// Whether to enable the feature flag cache for fetching remote configuration from the server.
         /// When enabled, the driver fetches feature flags from the Databricks server and merges them with local properties.
-        /// Default value is true if not specified.
+        /// Default value is false if not specified.
         /// </summary>
         public const string FeatureFlagCacheEnabled = "adbc.databricks.feature_flag_cache_enabled";
 

csharp/src/FeatureFlagCache.cs

@@ -307,9 +307,9 @@ public async Task<IReadOnlyDictionary<string, string>> MergePropertiesWithFeatur
 
             try
             {
-                // Check if feature flag cache is enabled (default: true)
-                if (localProperties.TryGetValue(DatabricksParameters.FeatureFlagCacheEnabled, out string? enabledStr) &&
-                    bool.TryParse(enabledStr, out bool enabled) &&
+                // Check if feature flag cache is enabled (default: false)
+                if (!localProperties.TryGetValue(DatabricksParameters.FeatureFlagCacheEnabled, out string? enabledStr) ||
+                    !bool.TryParse(enabledStr, out bool enabled) ||
                     !enabled)
                 {
                     activity?.AddEvent(new ActivityEvent("feature_flags.skipped",

csharp/test/Unit/FeatureFlagCacheTests.cs

@@ -567,6 +567,64 @@ public async Task FeatureFlagContext_BackgroundRefreshError_ContinuesRefreshLoop
 
         #endregion
 
+        #region MergePropertiesWithFeatureFlagsAsync Default Behavior Tests
+
+        [Fact]
+        public async Task MergePropertiesWithFeatureFlagsAsync_PropertyNotSet_ReturnsLocalProperties()
+        {
+            // Arrange - No FeatureFlagCacheEnabled property set (default: false)
+            var localProperties = new Dictionary<string, string>
+            {
+                ["host"] = TestHost,
+                ["some_property"] = "some_value"
+            };
+            var cache = FeatureFlagCache.GetInstance();
+
+            // Act
+            var result = await cache.MergePropertiesWithFeatureFlagsAsync(localProperties, DriverVersion);
+
+            // Assert - Should return local properties unchanged (feature flags skipped)
+            Assert.Same(localProperties, result);
+        }
+
+        [Fact]
+        public async Task MergePropertiesWithFeatureFlagsAsync_PropertySetToFalse_ReturnsLocalProperties()
+        {
+            // Arrange - FeatureFlagCacheEnabled explicitly set to false
+            var localProperties = new Dictionary<string, string>
+            {
+                ["host"] = TestHost,
+                [DatabricksParameters.FeatureFlagCacheEnabled] = "false"
+            };
+            var cache = FeatureFlagCache.GetInstance();
+
+            // Act
+            var result = await cache.MergePropertiesWithFeatureFlagsAsync(localProperties, DriverVersion);
+
+            // Assert - Should return local properties unchanged (feature flags skipped)
+            Assert.Same(localProperties, result);
+        }
+
+        [Fact]
+        public async Task MergePropertiesWithFeatureFlagsAsync_PropertySetToInvalidValue_ReturnsLocalProperties()
+        {
+            // Arrange - FeatureFlagCacheEnabled set to a non-boolean value
+            var localProperties = new Dictionary<string, string>
+            {
+                ["host"] = TestHost,
+                [DatabricksParameters.FeatureFlagCacheEnabled] = "notabool"
+            };
+            var cache = FeatureFlagCache.GetInstance();
+
+            // Act
+            var result = await cache.MergePropertiesWithFeatureFlagsAsync(localProperties, DriverVersion);
+
+            // Assert - Should return local properties unchanged (can't parse as bool)
+            Assert.Same(localProperties, result);
+        }
+
+        #endregion
+
         #region Helper Methods
 
         /// <summary>