Constant SHELL_INPUT_CH_SIZE 

const SHELL_INPUT_CH_SIZE: usize = 256;

Cap on the out-of-order input reorder buffer (input_seq_buf).

The input channel itself is now unbounded (unbounded_channel): a bounded try_send silently dropped input on burst (large pastes arriving faster than the PTY write loop drains — the original truncation bug), and the proper backpressure remedy (send().await) can’t be applied here because send_input is a synchronous trait method holding a std::Mutex. An unbounded channel guarantees no input is ever dropped; terminal input is human-paced (and the frontend now chunks large pastes at 4 KB / 5 ms), and the PTY drain loop keeps up, so the queue does not grow in practice. This constant only bounds the reorder buffer (pathological out-of-order seqs).