refactor(client): separate accepted negotiation state from peer evidence

crates/irtt-client/src/async_client.rs

@@ -654,9 +654,11 @@ impl AsyncClient {
         self.machine.probe_timeout()
     }
 
-    /// Negotiated parameters of the currently open session.
-    pub fn negotiated_params(&self) -> Option<&crate::NegotiatedParams> {
-        self.machine.negotiated_params()
+    /// Accepted semantics and exact peer parameters of the currently live session.
+    ///
+    /// Returns `None` before Open, after Close, and after no-test completion.
+    pub fn negotiation(&self) -> Option<&crate::NegotiationResult> {
+        self.machine.negotiation()
     }
 
     /// Whether any sent probes still await a reply or timeout.
@@ -707,17 +709,7 @@ impl AsyncClient {
                 return Err(Box::new(PreparedAsyncOpenFailure { primary, machine }));
             }
         };
-        let negotiated_traffic_class = match u8::try_from(negotiated.params.dscp) {
-            Ok(traffic_class) => traffic_class,
-            Err(_) => {
-                return Err(Box::new(PreparedAsyncOpenFailure {
-                    primary: ClientError::InvalidConfig {
-                        reason: "negotiated dscp must be in range 0..=255".to_owned(),
-                    },
-                    machine,
-                }));
-            }
-        };
+        let negotiated_traffic_class = negotiated.accepted.dscp << 2;
         let additional = recv_buffer_len.saturating_sub(self.recv_buffer.len());
         if let Err(source) = self.recv_buffer.try_reserve(additional) {
             return Err(Box::new(PreparedAsyncOpenFailure {