feat(gossip): GUILD_SYNC bundle for message history on join

Wire RPC.GUILD_SYNC through gossip mesh: gossipGuildSync broadcast,
_onGossip + simulateGossip handlers, and guild-sync event emission.

Existing peers push channel/message/attachment snapshots when new
members connect or MEMBER_JOIN is received. Phase 61 / v0.8.26.

Co-authored-by: Cursor <[email protected]>

index.js

@@ -401,6 +401,9 @@ class PearcordGuild extends EventEmitter {
     if (method === RPC.SOUND_PLAY) {
       this.emit('guild-sound-play', payload)
     }
+    if (method === RPC.GUILD_SYNC) {
+      this.emit('guild-sync', payload)
+    }
   }
 
   /** Deterministic gossip injection for Bare smokes (no live mesh). */
@@ -449,6 +452,10 @@ class PearcordGuild extends EventEmitter {
       this.emit('guild-sound-play', payload)
       return
     }
+    if (method === RPC.GUILD_SYNC) {
+      this.emit('guild-sync', payload)
+      return
+    }
     if (method === RPC.PROFILE_COSMETIC_UPDATE) {
       this.emit('profile-cosmetic', payload)
       return
@@ -496,6 +503,10 @@ class PearcordGuild extends EventEmitter {
     broadcastGossip(this, RPC.MEMBER_JOIN, member)
   }
 
+  gossipGuildSync (payload) {
+    return broadcastGossip(this, RPC.GUILD_SYNC, payload)
+  }
+
   gossipAttachmentMeta (attachment) {
     broadcastGossip(this, RPC.ATTACHMENT_META, attachment)
   }