[DorianZheng]

Summary

• Fix race condition in PTY mode where two readers competed for the same PTY master FD
• In PTY mode, stderr is now merged into stdout (single reader), following kata-containers pattern
• Non-PTY mode unchanged - still has separate stdout/stderr pipes

Problem

In PTY mode, the code incorrectly created two separate readers from the same PTY master:

let stdout_fd = dup(master.as_raw_fd())  // reader #1
let stderr_fd = dup(master.as_raw_fd())  // reader #2 - SAME underlying FD!

Both readers had their own BufReader, causing:

• Race conditions when reading
• Out-of-order output (chunks captured by "wrong" reader)
• Data appearing on stderr when it should be on stdout

Solution

Follow kata-containers pattern:

• Only ONE reader from PTY master → stdout
• Pass None for stderr in PTY mode
• All terminal output flows through single stdout stream

Changes

File	Change
exec_handle.rs	new() accepts Option<OwnedFd> for stderr
executor.rs	PTY: pass None, non-PTY: Some(stderr)
command.rs	Same pattern, fix reconcile_pty_fds

Test Plan

• Run interactivebox_example.py and verify output ordering
• Test commands mixing stdout/stderr: ls /nonexistent 2>&1