Rust's std::io::Stdout uses internal BufWriter that bypasses libc,
making stdbuf -oL useless. stderr is unbuffered by default in Rust,
so tracing output appears immediately in container logs.
Also reverts n_episodes debug cap back to 16384.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>