fix(network): remove destructive subscription cycling from ReformMesh (TM-B2)

Log analysis from chaos test TM-A1 revealed that subscription cycling
(unsubscribe/subscribe) in ReformMesh was destroying ALL existing gossipsub
meshes, not just the mesh for the reconnecting peer.

Timeline from logs:
- 23:22:18: Node1 receiving gossip from Node2 AND Node3 normally
- 23:22:19: ReformMesh triggered with subscription cycling
- 23:22:19+: ZERO gossip messages received from ANY peer

Root cause: When you unsubscribe() from a topic, gossipsub sends LEAVE
messages to ALL mesh peers for that topic. When you resubscribe(), the
mesh must be rebuilt via GRAFT - which is not guaranteed to happen.

Fix: Remove subscription cycling entirely. Only use add_explicit_peer()
which marks the peer for mesh inclusion without affecting other meshes.
Gossipsub will GRAFT the explicit peer during its next heartbeat (1s).

This preserves existing working meshes with other peers while still
ensuring the reconnecting peer is added to the mesh.

Author: michaelgpt

app/src/actors_v2/network/network_actor.rs

@@ -2630,24 +2630,27 @@ impl Handler<NetworkMessage> for NetworkActor {
                                     Some(SwarmCommand::ReformMesh { peer_id, topics }) => {
                                         use libp2p::gossipsub::IdentTopic;
 
-                                        // TM-B1 FIX: Subscription cycling IS needed for mesh formation.
-                                        // The feedback loop was caused by GossipPeerSubscribed handler
-                                        // triggering more ReformMesh commands - that handler has been
-                                        // removed. Now subscription cycling only happens once per
-                                        // reconnection (triggered from ConnectionEstablished with
-                                        // deduplication).
+                                        // TM-B2 FIX: DO NOT use subscription cycling!
                                         //
-                                        // How this works:
-                                        // 1. unsubscribe() removes us from topic
-                                        // 2. subscribe() re-joins topic, triggering mesh rebuild
-                                        // 3. Gossipsub sends GRAFT to connected peers for mesh formation
-                                        // 4. Remote peer receives SUBSCRIBE but no longer triggers ReformMesh
-                                        //    (GossipPeerSubscribed handler was removed)
+                                        // Log analysis from chaos test TM-A1 shows that subscription
+                                        // cycling (unsubscribe/subscribe) is DESTRUCTIVE:
+                                        // - It sends LEAVE messages to ALL mesh peers for each topic
+                                        // - This destroys existing working meshes with other peers
+                                        // - The mesh rebuild via GRAFT is not guaranteed
+                                        // - Result: node ends up with NO mesh peers after ReformMesh
+                                        //
+                                        // Instead, we ONLY call add_explicit_peer() which:
+                                        // - Marks the peer for inclusion in the mesh
+                                        // - Does NOT affect meshes with other peers
+                                        // - Gossipsub will GRAFT this peer during heartbeat (1s interval)
+                                        //
+                                        // For faster mesh formation after partition recovery, we also
+                                        // send publish_many_peers to trigger immediate IWANT/IHAVE
+                                        // exchanges which can help establish mesh connections.
 
                                         let gossipsub = &mut swarm.behaviour_mut().gossipsub;
 
-                                        // Check current mesh status
-                                        let mut needs_reform = false;
+                                        // Check current mesh status for logging
                                         let mut missing_topics = Vec::new();
                                         for topic_str in &topics {
                                             let topic = IdentTopic::new(topic_str);
@@ -2656,33 +2659,26 @@ impl Handler<NetworkMessage> for NetworkActor {
                                                 .mesh_peers(&topic_hash)
                                                 .any(|p| *p == peer_id);
                                             if !in_mesh {
-                                                needs_reform = true;
                                                 missing_topics.push(topic_str.clone());
                                             }
                                         }
 
-                                        if needs_reform {
+                                        if !missing_topics.is_empty() {
                                             tracing::info!(
                                                 peer_id = %peer_id,
-                                                topics_count = topics.len(),
                                                 missing_topics = ?missing_topics,
-                                                "ReformMesh: cycling subscriptions to trigger GRAFT"
+                                                "ReformMesh: adding explicit peer (no subscription cycling)"
                                             );
-
-                                            // Cycle subscriptions to trigger mesh rebuild with GRAFT
-                                            for topic_str in &topics {
-                                                let topic = IdentTopic::new(topic_str);
-                                                let _ = gossipsub.unsubscribe(&topic);
-                                                let _ = gossipsub.subscribe(&topic);
-                                            }
                                         } else {
                                             tracing::debug!(
                                                 peer_id = %peer_id,
                                                 "ReformMesh: peer already in mesh for all topics"
                                             );
                                         }
 
-                                        // Also add as explicit peer for reliable message delivery
+                                        // Add as explicit peer - this is the ONLY safe mesh formation method
+                                        // Explicit peers are always included in publish fanout and will
+                                        // receive GRAFT during the next gossipsub heartbeat
                                         gossipsub.add_explicit_peer(&peer_id);
                                     }