transport: extract tcp connection-pool types into pool.rs

Moves the inline TcpConnection/ConnectingEntry structs, the Direction
enum, and the ConnectionPool/ConnectingPool type aliases out of the
1147-line tcp/mod.rs into a dedicated pool.rs, matching the canonical
per-transport layout. Struct fields are pub(crate) so mod.rs can still
construct and read them across the module boundary. Pure relocation; no
logic change.

src/transport/tcp/mod.rs

@@ -22,6 +22,7 @@
 //! No additional framing overhead — packets are written directly to the
 //! TCP stream and the receiver uses phase-dependent size computation.
 
+mod pool;
 pub mod stats;
 
 use super::resolve_socket_addr;
@@ -31,6 +32,7 @@ use super::{
 };
 use crate::config::TcpConfig;
 use crate::transport::framing::read_fmp_packet;
+use pool::{ConnectingEntry, ConnectingPool, ConnectionPool, Direction, TcpConnection};
 use stats::TcpStats;
 
 use futures::FutureExt;
@@ -47,52 +49,6 @@ use tokio::task::JoinHandle;
 use tokio::time::Instant;
 use tracing::{debug, info, trace, warn};
 
-// ============================================================================
-// Connection Pool
-// ============================================================================
-
-/// Direction of a pooled connection, used to drive separate
-/// `pool_inbound` / `pool_outbound` accounting for the
-/// `max_inbound_connections` admission cap.
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-enum Direction {
-    /// Inbound — accepted by the listener.
-    Inbound,
-    /// Outbound — initiated by connect-on-send or background connect.
-    Outbound,
-}
-
-/// State for a single TCP connection to a peer.
-struct TcpConnection {
-    /// Write half of the split stream.
-    writer: Arc<Mutex<OwnedWriteHalf>>,
-    /// Receive task for this connection.
-    recv_task: JoinHandle<()>,
-    /// MSS-derived MTU for this connection (used for dynamic MTU re-reading).
-    #[allow(dead_code)]
-    mtu: u16,
-    /// When the connection was established.
-    #[allow(dead_code)]
-    established_at: Instant,
-    /// Direction of the connection — drives pool-inbound/outbound accounting.
-    direction: Direction,
-}
-
-/// Shared connection pool.
-type ConnectionPool = Arc<Mutex<HashMap<TransportAddr, TcpConnection>>>;
-
-/// A pending background connection attempt.
-///
-/// Holds the JoinHandle for a spawned TCP connect task. The task
-/// produces a configured `TcpStream` and MSS-derived MTU on success.
-struct ConnectingEntry {
-    /// Background task performing TCP connect + socket configuration.
-    task: JoinHandle<Result<(TcpStream, u16), TransportError>>,
-}
-
-/// Map of addresses with background connection attempts in progress.
-type ConnectingPool = Arc<Mutex<HashMap<TransportAddr, ConnectingEntry>>>;
-
 // ============================================================================
 // TCP Transport
 // ============================================================================

src/transport/tcp/pool.rs

@@ -0,0 +1,56 @@
+//! TCP connection pool types.
+//!
+//! Holds the per-connection state and the pooled/connecting maps used by the
+//! TCP transport.
+
+use std::collections::HashMap;
+use std::sync::Arc;
+use tokio::net::TcpStream;
+use tokio::net::tcp::OwnedWriteHalf;
+use tokio::sync::Mutex;
+use tokio::task::JoinHandle;
+use tokio::time::Instant;
+
+use crate::transport::{TransportAddr, TransportError};
+
+/// Direction of a pooled connection, used to drive separate
+/// `pool_inbound` / `pool_outbound` accounting for the
+/// `max_inbound_connections` admission cap.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) enum Direction {
+    /// Inbound — accepted by the listener.
+    Inbound,
+    /// Outbound — initiated by connect-on-send or background connect.
+    Outbound,
+}
+
+/// State for a single TCP connection to a peer.
+pub(crate) struct TcpConnection {
+    /// Write half of the split stream.
+    pub(crate) writer: Arc<Mutex<OwnedWriteHalf>>,
+    /// Receive task for this connection.
+    pub(crate) recv_task: JoinHandle<()>,
+    /// MSS-derived MTU for this connection (used for dynamic MTU re-reading).
+    #[allow(dead_code)]
+    pub(crate) mtu: u16,
+    /// When the connection was established.
+    #[allow(dead_code)]
+    pub(crate) established_at: Instant,
+    /// Direction of the connection — drives pool-inbound/outbound accounting.
+    pub(crate) direction: Direction,
+}
+
+/// Shared connection pool.
+pub(crate) type ConnectionPool = Arc<Mutex<HashMap<TransportAddr, TcpConnection>>>;
+
+/// A pending background connection attempt.
+///
+/// Holds the JoinHandle for a spawned TCP connect task. The task
+/// produces a configured `TcpStream` and MSS-derived MTU on success.
+pub(crate) struct ConnectingEntry {
+    /// Background task performing TCP connect + socket configuration.
+    pub(crate) task: JoinHandle<Result<(TcpStream, u16), TransportError>>,
+}
+
+/// Map of addresses with background connection attempts in progress.
+pub(crate) type ConnectingPool = Arc<Mutex<HashMap<TransportAddr, ConnectingEntry>>>;