port_forward_mux: pin permission revocation and whole-tunnel failure in tests

Both already hold; the review asked for them to be stated. `enable-tunnel`
turned off mid-session refuses the next `open` while the live channel
keeps relaying, and a dead tunnel ends every channel on it together,
after which the next accept establishes again on the same `Tunnel`.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EZ49AbZJYfm8NTp5yDPMab

src/port_forward_mux.rs

@@ -1311,14 +1311,27 @@ mod tests {
                 let t = Tunnel::new();
                 t.claim();
                 let h = t.set_muxed(ours, NoUi::default());
-                let (mut app, sock) = local_pair().await;
+                let (mut app_a, sock_a) = local_pair().await;
-                h.open("localhost", 1, sock, vec![]).unwrap();
+                let (mut app_b, sock_b) = local_pair().await;
+                h.open("localhost", 1, sock_a, vec![]).unwrap();
+                h.open("localhost", 1, sock_b, vec![]).unwrap();
                 drop(peer);
+                // One tunnel is one failure domain: every channel on it ends.
                 let mut buf = [0u8; 1];
-                assert_eq!(app.read(&mut buf).await.unwrap(), 0);
+                assert_eq!(app_a.read(&mut buf).await.unwrap(), 0);
+                assert_eq!(app_b.read(&mut buf).await.unwrap(), 0);
                 tokio::time::sleep(std::time::Duration::from_millis(50)).await;
-                assert!(matches!(t.claim(), Claim::Claimed));
                 assert!(h.open("localhost", 1, local_pair().await.1, vec![]).is_err());
+                // The next accept establishes again on the same `Tunnel`.
+                assert!(matches!(t.claim(), Claim::Claimed));
+                let (ours, mut peer) = stream_pair().await;
+                let h = t.set_muxed(ours, NoUi::default());
+                let (_app_c, sock_c) = local_pair().await;
+                h.open("localhost", 1, sock_c, vec![]).unwrap();
+                assert!(matches!(
+                    recv_frame(&mut peer).await.union,
+                    Some(port_forward_channel::Union::Open(_))
+                ));
             });
         }
 

src/server/port_forward_mux.rs

@@ -381,6 +381,24 @@ mod tests {
         });
     }
 
+    #[test]
+    fn a_revoked_permission_refuses_new_channels_and_keeps_live_ones() {
+        rt().block_on(async {
+            let port = echo_target().await;
+            let (tx, mut rx) = mpsc::unbounded_channel();
+            let mut mux = PortForwardMux::new(tx, format!("127.0.0.1:{}", port));
+            mux.handle(open(1, port), || true);
+            assert_eq!(opened(&next_frame(&mut rx).await), (1, true));
+            // `enable-tunnel` is consulted per `open`, so turning it off
+            // mid-session stops new channels; the live one keeps relaying.
+            mux.handle(open(2, port), || false);
+            assert_eq!(opened(&next_frame(&mut rx).await), (2, false));
+            mux.handle(data(1, b"still relayed"), || false);
+            assert_eq!(data_of(&next_frame(&mut rx).await), (1, b"still relayed".to_vec()));
+            assert_eq!(mux.live_channels(), 1);
+        });
+    }
+
     #[test]
     fn close_while_connecting_sends_no_opened() {
         rt().block_on(async {