[codex] fix Windows ConPTY input handling (#29734)

## Why

Windows unified-exec TTY input did not behave like the non-Windows PTY
path. ConPTY sessions could receive the wrong line ending or mishandle
backspace, especially when sending input to a foreground program through
PowerShell or cmd. The local, legacy restricted, and elevated paths also
handled this normalization separately.

## What changed

- share one stateful Windows TTY input normalizer across local, legacy
restricted, and elevated runner paths
- translate LF and split CRLF into one Windows terminal Enter, encode
backspace as DEL, and preserve UTF-8 and control bytes such as Ctrl-C
- add Windows integration coverage for Unicode input, backspace, Enter,
and PowerShell foreground-child Ctrl-C behavior

## Validation

- `just test -p codex-utils-pty` (13 tests passed; the Unicode
integration test retried once)
- the Unicode integration test passed five consecutive runs with retries
disabled
- integration coverage sends `cafeé 漢字` through cmd and PowerShell and
verifies that Ctrl-C interrupts a running PowerShell foreground child

codex-rs/utils/pty/src/windows_tests.rs

@@ -0,0 +1,157 @@
+use super::collect_output_until_exit;
+use super::combine_spawned_output;
+use super::find_python;
+use super::wait_for_output_contains;
+use crate::TerminalSize;
+use crate::spawn_pty_process;
+use std::collections::HashMap;
+use std::path::Path;
+
+const READY_MARKER: &str = "__CODEX_CHILD_READY__";
+const VALUE_MARKER: &str = "__CODEX_CHILD_VALUE__";
+
+struct WindowsShell {
+    name: &'static str,
+    program: String,
+    args: Vec<String>,
+    child_command: String,
+}
+
+fn find_powershell() -> Option<String> {
+    ["pwsh.exe", "powershell.exe"]
+        .into_iter()
+        .find_map(|candidate| {
+            std::process::Command::new(candidate)
+                .args(["-NoLogo", "-NoProfile", "-Command", "exit 0"])
+                .status()
+                .ok()
+                .filter(std::process::ExitStatus::success)
+                .map(|_| candidate.to_string())
+        })
+}
+
+fn utf8_hex(value: &str) -> String {
+    value
+        .as_bytes()
+        .iter()
+        .map(|byte| format!("{byte:02x}"))
+        .collect::<Vec<_>>()
+        .join("")
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn conpty_delivers_input_to_foreground_children() -> anyhow::Result<()> {
+    let Some(python) = find_python() else {
+        eprintln!("python not found; skipping ConPTY input test");
+        return Ok(());
+    };
+    let code = format!(
+        "print('__CODEX_CHILD_'+'READY__', flush=True); value=input(); print('{VALUE_MARKER}'+value.encode('utf-8').hex(), flush=True)"
+    );
+    let expected = "cafeé 漢字";
+    let expected_marker = format!("{VALUE_MARKER}{}", utf8_hex(expected));
+    let mut shells = vec![WindowsShell {
+        name: "cmd",
+        program: std::env::var("COMSPEC").unwrap_or_else(|_| "cmd.exe".to_string()),
+        args: vec!["/D".to_string(), "/Q".to_string()],
+        child_command: format!("\"{}\" -u -c \"{code}\"", python.replace('"', "\"\"")),
+    }];
+    if let Some(program) = find_powershell() {
+        shells.push(WindowsShell {
+            name: "PowerShell",
+            program,
+            args: vec!["-NoLogo".to_string(), "-NoProfile".to_string()],
+            child_command: format!("& '{}' -u -c \"{code}\"", python.replace('\'', "''")),
+        });
+    }
+    let env: HashMap<String, String> = std::env::vars().collect();
+
+    for shell in shells {
+        let spawned = spawn_pty_process(
+            &shell.program,
+            &shell.args,
+            Path::new("."),
+            &env,
+            /*arg0*/ &None,
+            TerminalSize::default(),
+        )
+        .await?;
+        let (session, mut output_rx, exit_rx) = combine_spawned_output(spawned);
+        let writer = session.writer_sender();
+        writer
+            .send(format!("{}\n", shell.child_command).into_bytes())
+            .await?;
+        wait_for_output_contains(&mut output_rx, READY_MARKER, /*timeout_ms*/ 10_000)
+            .await
+            .map_err(|err| anyhow::anyhow!("{} child did not become ready: {err}", shell.name))?;
+
+        writer
+            .send(format!("{expected}X\u{8}\n").into_bytes())
+            .await?;
+        let mut output =
+            wait_for_output_contains(&mut output_rx, &expected_marker, /*timeout_ms*/ 10_000)
+                .await
+                .map_err(|err| {
+                    anyhow::anyhow!("{} child received incorrect input: {err}", shell.name)
+                })?;
+
+        writer.send(b"exit 0\n".to_vec()).await?;
+        let (remaining, exit_code) =
+            collect_output_until_exit(output_rx, exit_rx, /*timeout_ms*/ 10_000).await;
+        output.extend_from_slice(&remaining);
+
+        assert_eq!(
+            exit_code,
+            0,
+            "{} did not exit cleanly: {:?}",
+            shell.name,
+            String::from_utf8_lossy(&output)
+        );
+    }
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn conpty_ctrl_c_interrupts_powershell_foreground_child() -> anyhow::Result<()> {
+    let Some(program) = find_powershell() else {
+        return Ok(());
+    };
+    let args = vec!["-NoLogo".to_string(), "-NoProfile".to_string()];
+    let env: HashMap<String, String> = std::env::vars().collect();
+    let spawned = spawn_pty_process(
+        &program,
+        &args,
+        Path::new("."),
+        &env,
+        /*arg0*/ &None,
+        TerminalSize::default(),
+    )
+    .await?;
+    let (session, mut output_rx, exit_rx) = combine_spawned_output(spawned);
+    let writer = session.writer_sender();
+    writer.send(b"ping.exe -4 -t localhost\n".to_vec()).await?;
+    wait_for_output_contains(&mut output_rx, "127.0.0.1", /*timeout_ms*/ 10_000).await?;
+
+    writer.send(vec![0x03]).await?;
+    tokio::time::sleep(tokio::time::Duration::from_millis(200)).await;
+    writer.send(b"cmd.exe /D /C ver\n".to_vec()).await?;
+    let mut output = wait_for_output_contains(
+        &mut output_rx,
+        "Microsoft Windows",
+        /*timeout_ms*/ 10_000,
+    )
+    .await?;
+
+    writer.send(b"exit 0\n".to_vec()).await?;
+    let (remaining, exit_code) =
+        collect_output_until_exit(output_rx, exit_rx, /*timeout_ms*/ 10_000).await;
+    output.extend_from_slice(&remaining);
+    assert_eq!(
+        exit_code,
+        0,
+        "PowerShell did not resume after Ctrl-C: {:?}",
+        String::from_utf8_lossy(&output)
+    );
+    Ok(())
+}