fix: initialize gossip after cluster services (#2361)

Author: rogeralsing

logs/log1755969060.md

@@ -0,0 +1,8 @@
+# Log 1755969060
+
+## Summary
+- Reordered `StartMemberAsync` to call `BeginStartAsync` before `StartGossipActorAsync`, ensuring `MemberList` and `Remote` are initialized before gossip starts.
+- Added a clarifying comment documenting the dependency.
+
+## Motivation
+`StartGossipActorAsync` accessed `MemberList` and the remote block list before they were initialized, leading to intermittent null-reference failures during cluster startup and tests.

src/Proto.Cluster/Cluster.cs

@@ -164,9 +164,9 @@ private void SubscribeToTopologyEvents() =>
     /// </summary>
     public async Task StartMemberAsync()
     {
+        await BeginStartAsync(false).ConfigureAwait(false); // ensure MemberList and Remote are initialized
         await Gossip.StartGossipActorAsync().ConfigureAwait(false);
-        await BeginStartAsync(false).ConfigureAwait(false);
-        //gossiper must be started whenever any topology events starts flowing
+        // gossiper must be started whenever any topology events starts flowing
         await Gossip.StartgossipLoopAsync().ConfigureAwait(false);
         MemberList.InitializeTopologyConsensus();
         await Provider.StartMemberAsync(this).ConfigureAwait(false);