Split protocol internals by responsibility

src/protocol/session/status.rs

@@ -0,0 +1,15 @@
+/// Session lifecycle status returned from [`Session::update`](super::Session::update).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum SessionStatus {
+    /// The session is active and should receive future update ticks.
+    Running,
+
+    /// The session is winding down but still needs future update ticks.
+    Closing,
+
+    /// The session has finished application work.
+    ///
+    /// The generated leaf removes the entry after the update tick. Final packets are
+    /// routed immediately by the session before returning this status.
+    Closed,
+}