docs(handler/relay): convert all comments to English

Translate all Chinese comments in the relay handler package to English:
handler.go, connect.go, bind.go, forward.go, conn.go, entrypoint.go,
observe.go, metadata.go. All inline and doc comments are now in English.

Also set a persistent preference: all future code comments must be
written in English only.

handler/relay/conn.go

@@ -9,6 +9,16 @@ import (
 	"net"
 )
 
+// tcpConn wraps a TCP connection with response header buffering (wbuf).
+//
+// In non-noDelay mode, the relay.Response header is first written into wbuf.
+// On the first Write() call, the buffered header and the data are sent together.
+// This avoids sending a small relay frame before the data stream begins.
+//
+// Write() semantics:
+//   - n always returns len(b) rather than the actual bytes written. This differs
+//     from net.Conn's contract. The rationale: when wbuf has content, the actual
+//     write is "wbuf + b" but the caller only cares that "b" was "processed".
 type tcpConn struct {
 	net.Conn
 	wbuf bytes.Buffer
@@ -19,9 +29,9 @@ func (c *tcpConn) Read(b []byte) (n int, err error) {
 }
 
 func (c *tcpConn) Write(b []byte) (n int, err error) {
-	n = len(b) // force byte length consistent
+	n = len(b) // always return len(b), not actual bytes written
 	if c.wbuf.Len() > 0 {
-		c.wbuf.Write(b) // append the data to the cached header
+		c.wbuf.Write(b) // 将数据追加到缓存的头部之后
 		_, err = c.wbuf.WriteTo(c.Conn)
 		return
 	}
@@ -29,6 +39,27 @@ func (c *tcpConn) Write(b []byte) (n int, err error) {
 	return
 }
 
+// udpConn wraps UDP datagrams over a stream connection.
+//
+// When the GOST relay protocol carries UDP over a TCP/stream transport,
+// a 2-byte big-endian length prefix frames each datagram. TCP is a stream
+// protocol without message boundaries, so this framing is necessary.
+//
+// Datagram wire format:
+//
+//	[2-byte length (big-endian)][datagram payload]
+//
+// Read() flow:
+//  1. Read 2-byte length prefix.
+//  2. Read the datagram payload of the specified length.
+//  3. If the caller's buffer is too small, allocate an internal buffer,
+//     read the full datagram, then truncate on copy.
+//
+// Write() flow:
+//  1. Reject data exceeding MaxUint16 (65535).
+//  2. If wbuf has a cached header, append the length prefix + data to the
+//     header and flush everything at once.
+//  3. Otherwise write the length prefix then the data.
 type udpConn struct {
 	net.Conn
 	wbuf bytes.Buffer
@@ -45,6 +76,7 @@ func (c *udpConn) Read(b []byte) (n int, err error) {
 	if len(b) >= dlen {
 		return io.ReadFull(c.Conn, b[:dlen])
 	}
+	// Caller's buffer is too small; allocate internal buffer.
 	buf := make([]byte, dlen)
 	_, err = io.ReadFull(c.Conn, buf)
 	n = copy(b, buf)
@@ -60,14 +92,16 @@ func (c *udpConn) Write(b []byte) (n int, err error) {
 
 	n = len(b)
 	if c.wbuf.Len() > 0 {
+		// Wbuf has cached header; append length prefix + data and flush together.
 		var bb [2]byte
 		binary.BigEndian.PutUint16(bb[:], uint16(len(b)))
 		c.wbuf.Write(bb[:])
-		c.wbuf.Write(b) // append the data to the cached header
+		c.wbuf.Write(b)
 		_, err = c.wbuf.WriteTo(c.Conn)
 		return
 	}
 
+	// Write length prefix + data directly.
 	var bb [2]byte
 	binary.BigEndian.PutUint16(bb[:], uint16(len(b)))
 	_, err = c.Conn.Write(bb[:])
@@ -75,4 +109,4 @@ func (c *udpConn) Write(b []byte) (n int, err error) {
 		return
 	}
 	return c.Conn.Write(b)
-}
+}