feat(wrapper): add UnwrapConn to remaining TCP conn wrappers

Add UnwrapConn() to the admission, proxyproto, conn limiter, metrics,
and observer/stats TCP connection wrappers, complementing the traffic
limiter's limitConn added in the previous commit.

This makes the unwrapConn() helper in handler/sshd able to peel through
any combination of these wrappers uniformly, keeping the pattern
complete and future-proof for handlers that assert on concrete
connection types.

admission/wrapper/conn.go

@@ -44,6 +44,12 @@ func WrapConn(admission admission.Admission, c net.Conn) net.Conn {
 	}
 }
 
+// UnwrapConn returns the underlying connection, allowing type assertions
+// through wrapper layers.
+func (c *serverConn) UnwrapConn() net.Conn {
+	return c.Conn
+}
+
 // Read checks the remote address against the admission controller
 // before delegating to the underlying connection. If denied, it returns
 // io.EOF to signal end-of-stream.

internal/net/proxyproto/conn.go

@@ -14,6 +14,12 @@ type serverConn struct {
 	ctx context.Context
 }
 
+// UnwrapConn returns the underlying connection, allowing type assertions
+// through wrapper layers.
+func (c *serverConn) UnwrapConn() net.Conn {
+	return c.Conn
+}
+
 func (c *serverConn) Context() context.Context {
 	return c.ctx
 }

limiter/conn/wrapper/conn.go

@@ -36,6 +36,12 @@ func WrapConn(limiter limiter.Limiter, c net.Conn) net.Conn {
 	}
 }
 
+// UnwrapConn returns the underlying connection, allowing type assertions
+// through wrapper layers.
+func (c *serverConn) UnwrapConn() net.Conn {
+	return c.Conn
+}
+
 func (c *serverConn) SyscallConn() (rc syscall.RawConn, err error) {
 	if sc, ok := c.Conn.(syscall.Conn); ok {
 		rc, err = sc.SyscallConn()

metrics/wrapper/conn.go

@@ -42,6 +42,12 @@ func WrapConn(service string, c net.Conn) net.Conn {
 	}
 }
 
+// UnwrapConn returns the underlying connection, allowing type assertions
+// through wrapper layers.
+func (c *serverConn) UnwrapConn() net.Conn {
+	return c.Conn
+}
+
 func (c *serverConn) Read(b []byte) (n int, err error) {
 	n, err = c.Conn.Read(b)
 	if counter := xmetrics.GetCounter(

observer/stats/wrapper/conn.go

@@ -45,6 +45,12 @@ func WrapConn(c net.Conn, pStats stats.Stats) net.Conn {
 	}
 }
 
+// UnwrapConn returns the underlying connection, allowing type assertions
+// through wrapper layers.
+func (c *conn) UnwrapConn() net.Conn {
+	return c.Conn
+}
+
 func (c *conn) Read(b []byte) (n int, err error) {
 	n, err = c.Conn.Read(b)
 	c.stats.Add(stats.KindInputBytes, int64(n))