node: Move state transition code to session

radicle-node/src/service.rs

@@ -603,16 +603,8 @@ where
         }
 
         if let Some(session) = self.sessions.get_mut(&remote) {
-            if let session::State::Connected { protocol, .. } = &mut session.state {
+            // Transition session back to gossip protocol.
-                if let session::Protocol::Fetch { .. } = protocol {
+            session.to_gossip();
-                    *protocol = session::Protocol::default();
-                } else {
-                    panic!(
-                        "Unexpected session state for {}: expected 'fetch' protocol, got 'gossip'",
-                        session.id
-                    );
-                }
-            }
             // Drain any messages in the session's outbox, which might have accumulated during the
             // fetch, and send them to the peer.
             self.reactor.drain(session);

radicle-node/src/service/session.rs

@@ -250,6 +250,19 @@ impl Session {
         *protocol = Protocol::Fetch { rid };
     }
 
+    pub fn to_gossip(&mut self) {
+        if let State::Connected { protocol, .. } = &mut self.state {
+            if let Protocol::Fetch { .. } = protocol {
+                *protocol = Protocol::default();
+            } else {
+                panic!(
+                    "Unexpected session state for {}: expected 'fetch' protocol, got 'gossip'",
+                    self.id
+                );
+            }
+        }
+    }
+
     pub fn to_connecting(&mut self) {
         assert!(
             self.is_disconnected(),