feat: adding piped process to replace PTY when needed (#8797)

codex-rs/utils/pty/README.md

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+# codex-utils-pty
+
+Lightweight helpers for spawning interactive processes either under a PTY (pseudo terminal) or regular pipes. The public API is minimal and mirrors both backends so callers can switch based on their needs (e.g., enabling or disabling TTY).
+
+## API surface
+
+- `spawn_pty_process(program, args, cwd, env, arg0)` → `SpawnedProcess`
+- `spawn_pipe_process(program, args, cwd, env, arg0)` → `SpawnedProcess`
+- `conpty_supported()` → `bool` (Windows only; always true elsewhere)
+- `ProcessHandle` exposes:
+  - `writer_sender()` → `mpsc::Sender<Vec<u8>>` (stdin)
+  - `output_receiver()` → `broadcast::Receiver<Vec<u8>>` (stdout/stderr merged)
+  - `has_exited()`, `exit_code()`, `terminate()`
+- `SpawnedProcess` bundles `handle`, `output_rx`, and `exit_rx` (oneshot exit code).
+
+## Usage examples
+
+```rust
+use std::collections::HashMap;
+use std::path::Path;
+use codex_utils_pty::spawn_pty_process;
+
+# tokio_test::block_on(async {
+let env_map: HashMap<String, String> = std::env::vars().collect();
+let spawned = spawn_pty_process(
+    "bash",
+    &["-lc".into(), "echo hello".into()],
+    Path::new("."),
+    &env_map,
+    &None,
+).await?;
+
+let writer = spawned.session.writer_sender();
+writer.send(b"exit\n".to_vec()).await?;
+
+// Collect output until the process exits.
+let mut output_rx = spawned.output_rx;
+let mut collected = Vec::new();
+while let Ok(chunk) = output_rx.try_recv() {
+    collected.extend_from_slice(&chunk);
+}
+let exit_code = spawned.exit_rx.await.unwrap_or(-1);
+# let _ = (collected, exit_code);
+# anyhow::Ok(())
+# });
+```
+
+Swap in `spawn_pipe_process` for a non-TTY subprocess; the rest of the API stays the same.
+
+## Tests
+
+Unit tests live in `src/lib.rs` and cover both backends (PTY Python REPL and pipe-based stdin roundtrip). Run with:
+
+```
+cargo test -p codex-utils-pty -- --nocapture
+```