chore: Ensure transition to falling back state based on synchronizer failure.

Author: kinyoklion

pkgs/sdk/server/src/Internal/FDv2DataSources/FDv2DataSource.InitializationTracker.cs

@@ -255,6 +255,13 @@ public void UpdateStatus(DataSourceState newState, DataSourceStatus.ErrorInfo? n
                     case DataSourceCategory.Synchronizers when newState == DataSourceState.Off:
                     {
                         DetermineState(Action.SynchronizersExhausted);
+                        // Currently, FDv1 fallback happens in the synchronizers group. If something from that group
+                        // reports Off, with a reason indicating that it should fallback to v1, then we can
+                        // transition to that state.
+                        if (newError.HasValue && newError.Value.FDv1Fallback)
+                        {
+                            DetermineState(Action.FallingBack);
+                        }
                         break;
                     }
                     case DataSourceCategory.FallbackSynchronizers when newState == DataSourceState.Off:
@@ -264,6 +271,8 @@ public void UpdateStatus(DataSourceState newState, DataSourceStatus.ErrorInfo? n
                     }
                     case DataSourceCategory.FallbackSynchronizers when newState == DataSourceState.Initializing:
                     {
+                        // In the normal flow this will have be already handled via the `Off` state of the
+                        // synchronizers. This is purely redundant in the current implementation.
                         DetermineState(Action.FallingBack);
                         break;
                     }