Implement SSH X11 forwarding Phase 2

- Add 'x11' channel type in handle_channel_open()
- Add handle_x11_channel_open() method
- Add 'x11-req' request in handle_channel_request()
- Add handle_x11_request() method
- Parse x11-req parameters (single_connection, auth_protocol, auth_cookie, screen_number)
- Create X11ForwardContext from DISPLAY env

All 182 tests pass.

markbase-core/src/ssh_server/channel.rs

@@ -129,6 +129,16 @@ impl ChannelManager {
                     maximum_packet_size,
                 )
             }
+            
+            "x11" => {
+                // Phase 2: X11 forwarding channel (RFC 4254 §7.2)
+                info!("Received x11 channel open (X11 forwarding)");
+                self.handle_x11_channel_open(
+                    sender_channel,
+                    initial_window_size,
+                    maximum_packet_size,
+                )
+            }
 
             _ => {
                 warn!("Unsupported channel type: {}", channel_type);
@@ -373,6 +383,68 @@ impl ChannelManager {
             maximum_packet_size,
         )
     }
+    
+    /// Phase 2: 处理x11 channel open（RFC 4254 §7.2）
+    fn handle_x11_channel_open(
+        &mut self,
+        sender_channel: u32,
+        initial_window_size: u32,
+        maximum_packet_size: u32,
+    ) -> Result<SshPacket> {
+        info!("Processing x11 channel open");
+        
+        // 创建 X11ForwardContext（从 DISPLAY 环境变量）
+        let display = std::env::var("DISPLAY").unwrap_or_else(|_| ":0".to_string());
+        let x11_ctx = super::x11_forward::X11ForwardContext::new(&display)?;
+        
+        let server_channel = self.next_channel_id;
+        self.next_channel_id += 1;
+        
+        let channel = Channel {
+            server_channel,
+            sender_channel,
+            channel_type: "x11".to_string(),
+            
+            // Phase 15: Window Control
+            remote_window: initial_window_size,
+            remote_maxpacket: maximum_packet_size,
+            local_window: 2097152,
+            local_window_max: 2097152,
+            local_consumed: 0,
+            local_maxpacket: 32768,
+            
+            window_size: initial_window_size,
+            maximum_packet_size,
+            state: ChannelState::Open,
+            output_buffer: None,
+            sftp_handler: None,
+            scp_handler: None,
+            rsync_handler: None,
+            exec_process: None,
+            exit_status: None,
+            sftp_input_buffer: Vec::new(),
+            scp_input_buffer: Vec::new(),
+            scp_state: ScpState::Idle,
+            scp_output_file: None,
+            direct_tcpip: None,
+            forwarded_tcpip: None,
+            auth_agent_socket: None,
+        };
+        
+        self.channels.insert(server_channel, channel);
+        
+        info!(
+            "x11 channel created: server_channel={}, display={}",
+            server_channel, display
+        );
+        
+        self.build_channel_open_confirmation(
+            server_channel,
+            sender_channel,
+            initial_window_size,
+            maximum_packet_size,
+        )
+    }
     /// 处理SSH_MSG_CHANNEL_REQUEST（参考OpenSSH channel.c: channel_request())
     pub fn handle_channel_request(&mut self, packet: &SshPacket) -> Result<Option<SshPacket>> {
         info!("Processing SSH_MSG_CHANNEL_REQUEST");
@@ -414,6 +486,9 @@ impl ChannelManager {
             self.handle_pty_request(&mut cursor, recipient_channel, want_reply) // 移除?操作符
         } else if request_type == "auth-agent-req@openssh.com" {
             self.handle_auth_agent_request(recipient_channel, want_reply)
+        } else if request_type == "x11-req" {
+            // Phase 2: X11 forwarding request (RFC 4254 §7.2)
+            self.handle_x11_request(&mut cursor, recipient_channel, want_reply)
         } else {
             warn!("Unsupported channel request: {}", request_type);
             if want_reply {
@@ -1406,6 +1481,50 @@ impl ChannelManager {
             }
         }
     }
+    
+    /// Phase 2: 处理x11-req请求（RFC 4254 §7.2）
+    fn handle_x11_request(
+        &mut self,
+        cursor: &mut std::io::Cursor<&[u8]>,
+        channel: u32,
+        want_reply: bool,
+    ) -> Result<Option<SshPacket>> {
+        info!("Handling x11-req request for channel {}", channel);
+        
+        // 读取 x11-req 参数（RFC 4254 §7.2）
+        // single_connection: boolean
+        let single_connection = cursor.read_u8()? != 0;
+        
+        // auth_protocol: SSH string (e.g., "MIT-MAGIC-COOKIE-1")
+        let auth_protocol = read_ssh_string(cursor)?;
+        
+        // auth_cookie: SSH string (hex-encoded cookie)
+        let auth_cookie_hex = read_ssh_string(cursor)?;
+        
+        // screen_number: u32
+        let screen_number = cursor.read_u32::<BigEndian>()?;
+        
+        info!(
+            "x11-req: single={}, protocol={}, screen={}",
+            single_connection, auth_protocol, screen_number
+        );
+        
+        // 创建 X11ForwardContext
+        let display = std::env::var("DISPLAY").unwrap_or_else(|_| ":0".to_string());
+        let x11_ctx = super::x11_forward::X11ForwardContext::new(&display)?;
+        
+        // 设置 DISPLAY 环境变量（client 会使用）
+        // Server 需要在 exec/shell 环境中设置 DISPLAY
+        // 这里只是记录，实际设置在 exec/shell handler 中
+        
+        info!("X11 forwarding enabled: display={}", x11_ctx.display_env());
+        
+        if want_reply {
+            Ok(Some(self.build_channel_success(channel)?))
+        } else {
+            Ok(None)
+        }
+    }
 
     /// ⭐⭐⭐⭐⭐ Phase 17: Check if a specific channel has an exec process
     pub fn channel_has_exec_process(&self, channel_id: u32) -> bool {
@@ -1685,9 +1804,9 @@ impl ChannelManager {
                                                     if let Some(hook) = &self.upload_hook {
                                                         if let Err(e) = hook.trigger(&path, &self.user_uuid) {
                                                             warn!("Upload hook failed for {:?}: {}", path, e);
-                                                        }
+}
-                                                    }
+        }
-                                                }
+    }
                                             }
 
                                             // 没有剩余数据，返回child_exited标志