Start Phase 14.4: SCP packet accumulation (Part 1)

**Implementation Started**:
- Added scp_input_buffer field to Channel struct (3 locations)
- Field initialization in all Channel creation
- Build successful (181 warnings)

**Testing**:
- SCP 2MB still fails (expected, handler logic not modified)
- Connection closed by remote host
- Need to modify scp_handler.rs next

**Next Steps**:
- Modify scp_handler.rs handle_file_command()
- Use scp_input_buffer for data accumulation
- Similar to SFTP accumulation logic (Phase 14.3)

**Progress**: Phase 14.4 started (50% complete)

**Tool Calls**: Reached 200 limit, session ending

markbase-core/src/ssh_server/channel.rs

@@ -124,6 +124,7 @@ impl ChannelManager {
             rsync_handler: None,
             exec_process: None,  // Phase 14: 交互式exec
             sftp_input_buffer: Vec::new(),  // ⭐⭐⭐⭐⭐ Phase 14.2修复：SFTP packet累积
+            scp_input_buffer: Vec::new(),   // ⭐⭐⭐⭐⭐ Phase 14.4修复：SCP packet累积
             direct_tcpip: None,
             forwarded_tcpip: None,
         };
@@ -180,6 +181,7 @@ impl ChannelManager {
             rsync_handler: None,
             exec_process: None,  // Phase 14: 交互式exec
             sftp_input_buffer: Vec::new(),  // ⭐⭐⭐⭐⭐ Phase 14.2修复
+            scp_input_buffer: Vec::new(),   // ⭐⭐⭐⭐⭐ Phase 14.4修复
             direct_tcpip: Some(direct_tcpip),
             forwarded_tcpip: None,
         };
@@ -224,6 +226,7 @@ impl ChannelManager {
             rsync_handler: None,
             exec_process: None,  // Phase 14: 交互式exec
             sftp_input_buffer: Vec::new(),  // ⭐⭐⭐⭐⭐ Phase 14.2修复
+            scp_input_buffer: Vec::new(),   // ⭐⭐⭐⭐⭐ Phase 14.4修复
             direct_tcpip: None,
             forwarded_tcpip: Some(forwarded_tcpip),
         };
@@ -1321,6 +1324,8 @@ struct Channel {
     exec_process: Option<ExecProcess>,  // Phase 14: 交互式exec进程
     // ⭐⭐⭐⭐⭐ Critical修复：SFTP packet累积buffer
     sftp_input_buffer: Vec<u8>,  // Phase 14.2修复：累积不完整的SFTP packets
+    // ⭐⭐⭐⭐⭐ Phase 14.4：SCP packet累积buffer
+    scp_input_buffer: Vec<u8>,   // Phase 14.4修复：累积不完整的SCP packets
     // Phase 13.3: 端口转发相关字段
     direct_tcpip: Option<DirectTcpipChannel>,  // direct-tcpip channel（Remote forwarding）
     forwarded_tcpip: Option<ForwardedTcpipChannel>,  // forwarded-tcpip channel（Local forwarding）