fix(ffe): replace refreshed remote config

Author: leoromanovsky

tracer/src/Datadog.Trace/FeatureFlags/Rcm/FfeProduct.cs

@@ -51,7 +51,18 @@ public ApplyDetails[] UpdateFromRcm(Dictionary<string, List<RemoteConfiguration>
                     var serverConfigFile = new NamedRawFile(ffeConfig.Path, ffeConfig.Contents).Deserialize<ServerConfiguration>();
                     if (serverConfigFile.TypedFile is not null)
                     {
-                        _serverConfigurations.Add(new KeyValuePair<string, ServerConfiguration>(ffeConfig.Path.Path, serverConfigFile.TypedFile));
+                        var path = ffeConfig.Path.Path;
+                        var updatedConfig = new KeyValuePair<string, ServerConfiguration>(path, serverConfigFile.TypedFile);
+                        var existingIndex = _serverConfigurations.FindIndex(config => config.Key == path);
+                        if (existingIndex >= 0)
+                        {
+                            _serverConfigurations[existingIndex] = updatedConfig;
+                        }
+                        else
+                        {
+                            _serverConfigurations.Add(updatedConfig);
+                        }
+
                         res.Add(ApplyDetails.FromOk(ffeConfig.Path.Path));
                         apply = true;
                     }

tracer/test/Datadog.Trace.Tests/FeatureFlags/FeatureFlagsModuleTests.cs

@@ -75,6 +75,46 @@ public void UpdateRemoteConfig_WithEmptyList_InvokesCallbackAndReturnsProviderNo
         result.Reason.Should().Be(EvaluationReason.Error);
     }
 
+    [Fact]
+    public void UpdateRemoteConfig_WithExistingPath_ReplacesPreviousConfiguration()
+    {
+        var rcmManager = new MockRcmSubscriptionManager();
+        var module = new FeatureFlagsModule(CreateSettings(), rcmManager);
+        var configPath = RemoteConfigurationPath.FromPath($"datadog/2/{RcmProducts.FfeFlags}/test-config/config");
+
+        rcmManager.LastSubscription!.Invoke(
+            new Dictionary<string, List<RemoteConfiguration>>
+            {
+                [RcmProducts.FfeFlags] = [CreateRemoteConfiguration(configPath, "old-flag")]
+            },
+            null);
+
+        module.Evaluate("old-flag", FeatureFlagsValueType.Boolean, false, "user-1", null).Error.Should().BeNull();
+
+        rcmManager.LastSubscription.Invoke(
+            new Dictionary<string, List<RemoteConfiguration>>
+            {
+                [RcmProducts.FfeFlags] = [CreateRemoteConfiguration(configPath, "new-flag")]
+            },
+            null);
+
+        module.Evaluate("old-flag", FeatureFlagsValueType.Boolean, false, "user-1", null).Error.Should().Be("FLAG_NOT_FOUND");
+        module.Evaluate("new-flag", FeatureFlagsValueType.Boolean, false, "user-1", null).Error.Should().BeNull();
+    }
+
+    private static RemoteConfiguration CreateRemoteConfiguration(RemoteConfigurationPath configPath, string flagKey)
+    {
+        var configJson = JsonConvert.SerializeObject(new ServerConfiguration
+        {
+            Flags = new FlagCollection
+            {
+                [flagKey] = new Flag { Key = flagKey, Enabled = true, VariationType = FeatureFlagsValueType.Boolean }
+            }
+        });
+        var configBytes = System.Text.Encoding.UTF8.GetBytes(configJson);
+        return new RemoteConfiguration(configPath, configBytes, configBytes.Length, new Dictionary<string, string> { { "sha256", "dummy" } }, 1);
+    }
+
     private static TracerSettings CreateSettings()
     {
         var collection = new NameValueCollection