Constant SCP_IO_CHUNK 

pub const SCP_IO_CHUNK: usize = _; // 32_768usize

Stream chunk size for SCP file I/O (bytes). Never load whole files into RAM.

B4: this value used to be declared twice as a function-local const inside src/ssh/client_real_scp.rs, each carrying a deferral marker admitting it belonged here. It is deliberately equal to SFTP_IO_CHUNK — both transfer paths stream through the same window — but kept as a distinct name so a future protocol-specific tuning of one does not silently retune the other.