Add TCP transport node-level integration tests

Five tests covering the full TCP transport stack at the node level:
two-node handshake, three-node chain convergence with bloom filter
reachability, mixed UDP+TCP transport coexistence, MMP link-dead
detection after connection loss, and reconnection after link death
via connect-on-send.

src/node/tests/mod.rs

@@ -14,6 +14,7 @@ mod handshake;
 mod routing;
 mod session;
 mod spanning_tree;
+mod tcp;
 mod unit;
 
 pub(super) fn make_node() -> Node {

src/node/tests/tcp.rs

@@ -0,0 +1,279 @@
+//! TCP transport integration tests.
+//!
+//! Tests that the TCP transport works end-to-end at the node level:
+//! handshake, spanning tree convergence, mixed-transport routing,
+//! MMP link-dead detection, and reconnection after link death.
+//! All tests use 127.0.0.1:0 (ephemeral ports) and need no privileges.
+
+use super::*;
+use crate::config::TcpConfig;
+use crate::transport::tcp::TcpTransport;
+use crate::transport::{packet_channel, TransportAddr, TransportHandle, TransportId};
+use spanning_tree::{
+    cleanup_nodes, drain_all_packets, initiate_handshake, verify_tree_convergence, TestNode,
+};
+use std::time::Duration;
+
+/// Create a test node with a live TCP transport on loopback.
+///
+/// Parallel to `make_test_node()` in spanning_tree.rs but uses
+/// TcpTransport instead of UDP. Binds to 127.0.0.1:0 for an
+/// ephemeral port.
+async fn make_test_node_tcp() -> TestNode {
+    let mut node = make_node();
+    let transport_id = TransportId::new(1);
+
+    let config = TcpConfig {
+        bind_addr: Some("127.0.0.1:0".to_string()),
+        mtu: Some(1400),
+        ..Default::default()
+    };
+
+    let (packet_tx, packet_rx) = packet_channel(256);
+    let mut transport = TcpTransport::new(transport_id, None, config, packet_tx);
+    transport.start_async().await.unwrap();
+
+    let local_addr = transport
+        .local_addr()
+        .expect("TCP transport should have local addr after start");
+    let addr = TransportAddr::from_string(&local_addr.to_string());
+
+    node.transports
+        .insert(transport_id, TransportHandle::Tcp(transport));
+
+    TestNode {
+        node,
+        transport_id,
+        packet_rx,
+        addr,
+    }
+}
+
+/// Two TCP nodes complete a Noise handshake and establish bidirectional peering.
+#[tokio::test]
+async fn test_tcp_two_node_handshake() {
+    let mut nodes = vec![make_test_node_tcp().await, make_test_node_tcp().await];
+
+    // Initiate handshake from node 0 to node 1
+    initiate_handshake(&mut nodes, 0, 1).await;
+
+    // Drain all packets (handshake msg1/msg2 + TreeAnnounce exchange)
+    let total = drain_all_packets(&mut nodes, false).await;
+    assert!(total > 0, "should have processed packets");
+
+    // Verify bidirectional peering
+    let addr_0 = *nodes[0].node.node_addr();
+    let addr_1 = *nodes[1].node.node_addr();
+    assert!(
+        nodes[0].node.get_peer(&addr_1).is_some(),
+        "node 0 should have node 1 as peer"
+    );
+    assert!(
+        nodes[1].node.get_peer(&addr_0).is_some(),
+        "node 1 should have node 0 as peer"
+    );
+
+    cleanup_nodes(&mut nodes).await;
+}
+
+/// Three TCP nodes in a chain converge to a consistent spanning tree.
+///
+/// Chain: 0 -- 1 -- 2. Verifies tree convergence, peer counts, and
+/// bloom filter reachability across multiple hops.
+#[tokio::test]
+async fn test_tcp_three_node_chain() {
+    let mut nodes = vec![
+        make_test_node_tcp().await,
+        make_test_node_tcp().await,
+        make_test_node_tcp().await,
+    ];
+
+    // Chain: 0 -- 1 -- 2
+    initiate_handshake(&mut nodes, 0, 1).await;
+    initiate_handshake(&mut nodes, 1, 2).await;
+
+    let total = drain_all_packets(&mut nodes, false).await;
+    assert!(total > 0, "should have processed packets");
+
+    // Verify spanning tree convergence
+    verify_tree_convergence(&nodes);
+
+    // Verify correct root (smallest NodeAddr)
+    let expected_root = nodes.iter().map(|tn| *tn.node.node_addr()).min().unwrap();
+    for tn in &nodes {
+        assert_eq!(*tn.node.tree_state().root(), expected_root);
+    }
+
+    // Verify peer counts
+    assert_eq!(nodes[0].node.peer_count(), 1, "endpoint should have 1 peer");
+    assert_eq!(
+        nodes[1].node.peer_count(),
+        2,
+        "middle node should have 2 peers"
+    );
+    assert_eq!(nodes[2].node.peer_count(), 1, "endpoint should have 1 peer");
+
+    // Verify bloom filter reachability: node 0 can reach node 2 via node 1
+    let addr_2 = *nodes[2].node.node_addr();
+    let reaches = nodes[0].node.peers().any(|p| p.may_reach(&addr_2));
+    assert!(
+        reaches,
+        "node 0 should see node 2 as reachable through bloom filters"
+    );
+
+    cleanup_nodes(&mut nodes).await;
+}
+
+/// Mixed transport: UDP and TCP nodes coexist in the same test.
+///
+/// Two UDP nodes and two TCP nodes each form independent components.
+/// Validates that `process_available_packets()` handles heterogeneous
+/// transport types correctly.
+#[tokio::test]
+async fn test_tcp_mixed_transport_coexistence() {
+    use spanning_tree::{make_test_node, verify_tree_convergence_components};
+
+    // Create 2 UDP nodes and 2 TCP nodes
+    let udp_0 = make_test_node().await;
+    let udp_1 = make_test_node().await;
+    let tcp_0 = make_test_node_tcp().await;
+    let tcp_1 = make_test_node_tcp().await;
+
+    let mut nodes = vec![udp_0, udp_1, tcp_0, tcp_1];
+
+    // Handshake within each component
+    initiate_handshake(&mut nodes, 0, 1).await; // UDP pair
+    initiate_handshake(&mut nodes, 2, 3).await; // TCP pair
+
+    let total = drain_all_packets(&mut nodes, false).await;
+    assert!(total > 0);
+
+    // Verify each component converges independently
+    verify_tree_convergence_components(&nodes, &[vec![0, 1], vec![2, 3]]);
+
+    // TCP component has its own root
+    let tcp_root = std::cmp::min(*nodes[2].node.node_addr(), *nodes[3].node.node_addr());
+    assert_eq!(*nodes[2].node.tree_state().root(), tcp_root);
+    assert_eq!(*nodes[3].node.tree_state().root(), tcp_root);
+
+    cleanup_nodes(&mut nodes).await;
+}
+
+/// TCP connection drop is detected by MMP link-dead timeout.
+///
+/// Establishes peering, force-closes the TCP connection, then verifies
+/// that `check_link_heartbeats()` detects the dead peer after the
+/// link-dead timeout fires.
+#[tokio::test]
+async fn test_tcp_connection_loss_detection() {
+    let mut nodes = vec![make_test_node_tcp().await, make_test_node_tcp().await];
+
+    // Short heartbeat/link-dead timeouts for faster test execution
+    for tn in nodes.iter_mut() {
+        tn.node.config.node.heartbeat_interval_secs = 1;
+        tn.node.config.node.link_dead_timeout_secs = 3;
+    }
+
+    // Establish peering
+    initiate_handshake(&mut nodes, 0, 1).await;
+    let total = drain_all_packets(&mut nodes, false).await;
+    assert!(total > 0);
+
+    let addr_0 = *nodes[0].node.node_addr();
+    let addr_1 = *nodes[1].node.node_addr();
+    assert!(nodes[0].node.get_peer(&addr_1).is_some());
+    assert!(nodes[1].node.get_peer(&addr_0).is_some());
+
+    // Force-close the TCP connection on node 0's side toward node 1
+    let node1_listen_addr = nodes[1].addr.clone();
+    let transport = nodes[0]
+        .node
+        .transports
+        .get(&nodes[0].transport_id)
+        .unwrap();
+    transport.close_connection(&node1_listen_addr).await;
+
+    // Wait for link-dead timeout to fire (3 seconds + margin)
+    tokio::time::sleep(Duration::from_secs(4)).await;
+
+    // Trigger heartbeat check (normally done by the tick handler)
+    nodes[0].node.check_link_heartbeats().await;
+
+    // Node 0 should have detected node 1 as dead and removed it
+    assert!(
+        nodes[0].node.get_peer(&addr_1).is_none(),
+        "node 0 should have removed dead peer node 1"
+    );
+
+    cleanup_nodes(&mut nodes).await;
+}
+
+/// TCP reconnection after link death: connect-on-send re-establishes the link.
+///
+/// After both peers detect a dead link and remove each other, a fresh
+/// handshake triggers TCP connect-on-send to open a new connection.
+/// Verifies that bidirectional peering is restored.
+#[tokio::test]
+async fn test_tcp_reconnection_after_link_death() {
+    let mut nodes = vec![make_test_node_tcp().await, make_test_node_tcp().await];
+
+    // Short timeouts
+    for tn in nodes.iter_mut() {
+        tn.node.config.node.heartbeat_interval_secs = 1;
+        tn.node.config.node.link_dead_timeout_secs = 3;
+    }
+
+    // Establish initial peering
+    initiate_handshake(&mut nodes, 0, 1).await;
+    let total = drain_all_packets(&mut nodes, false).await;
+    assert!(total > 0);
+
+    let addr_0 = *nodes[0].node.node_addr();
+    let addr_1 = *nodes[1].node.node_addr();
+    assert!(nodes[0].node.get_peer(&addr_1).is_some());
+
+    // Force-close the TCP connection on node 0's side
+    let node1_listen_addr = nodes[1].addr.clone();
+    let transport = nodes[0]
+        .node
+        .transports
+        .get(&nodes[0].transport_id)
+        .unwrap();
+    transport.close_connection(&node1_listen_addr).await;
+
+    // Wait for link-dead timeout
+    tokio::time::sleep(Duration::from_secs(4)).await;
+
+    // Trigger dead peer removal on both sides
+    nodes[0].node.check_link_heartbeats().await;
+    nodes[1].node.check_link_heartbeats().await;
+
+    // Both should have removed the peer
+    assert!(
+        nodes[0].node.get_peer(&addr_1).is_none(),
+        "node 0 should have removed node 1"
+    );
+    assert!(
+        nodes[1].node.get_peer(&addr_0).is_none(),
+        "node 1 should have removed node 0"
+    );
+
+    // Re-initiate handshake — triggers TCP connect-on-send
+    initiate_handshake(&mut nodes, 0, 1).await;
+
+    // Drain to complete handshake + tree announce
+    let total2 = drain_all_packets(&mut nodes, false).await;
+    assert!(total2 > 0, "should have processed reconnection packets");
+
+    // Verify re-established peering
+    assert!(
+        nodes[0].node.get_peer(&addr_1).is_some(),
+        "node 0 should have re-established peer node 1"
+    );
+    assert!(
+        nodes[1].node.get_peer(&addr_0).is_some(),
+        "node 1 should have re-established peer node 0"
+    );
+
+    cleanup_nodes(&mut nodes).await;
+}