Allow multiple SystemConnects to be handled from a single node in the shard

backend/common/src/assign_id.rs

@@ -69,4 +69,8 @@ impl <Details> AssignId<Details> where Details: Eq + Hash + Clone {
     pub fn clear(&mut self) {
         *self = AssignId::new()
     }
+
+    pub fn iter(&self) -> impl Iterator<Item = (Id, &Details)> {
+        self.from_id.iter().map(|(id, details)| (*id, details))
+    }
 }

backend/common/src/internal_messages.rs

@@ -26,6 +26,10 @@ pub enum FromShardAggregator {
         local_id: LocalId,
         payload: Payload,
     },
+    /// Inform the core that a node has been removed
+    RemoveNode {
+        local_id: LocalId
+    }
 }
 
 /// Message sent form the backend core to the shard