Move TUI on top of app server (parallel code) (#14717)

This PR replicates the `tui` code directory and creates a temporary
parallel `tui_app_server` directory. It also implements a new feature
flag `tui_app_server` to select between the two tui implementations.

Once the new app-server-based TUI is stabilized, we'll delete the old
`tui` directory and feature flag.

codex-rs/tui_app_server/src/exec_command.rs

@@ -0,0 +1,70 @@
+use std::path::Path;
+use std::path::PathBuf;
+
+use codex_shell_command::parse_command::extract_shell_command;
+use dirs::home_dir;
+use shlex::try_join;
+
+pub(crate) fn escape_command(command: &[String]) -> String {
+    try_join(command.iter().map(String::as_str)).unwrap_or_else(|_| command.join(" "))
+}
+
+pub(crate) fn strip_bash_lc_and_escape(command: &[String]) -> String {
+    if let Some((_, script)) = extract_shell_command(command) {
+        return script.to_string();
+    }
+    escape_command(command)
+}
+
+/// If `path` is absolute and inside $HOME, return the part *after* the home
+/// directory; otherwise, return the path as-is. Note if `path` is the homedir,
+/// this will return and empty path.
+pub(crate) fn relativize_to_home<P>(path: P) -> Option<PathBuf>
+where
+    P: AsRef<Path>,
+{
+    let path = path.as_ref();
+    if !path.is_absolute() {
+        // If the path is not absolute, we can’t do anything with it.
+        return None;
+    }
+
+    let home_dir = home_dir()?;
+    let rel = path.strip_prefix(&home_dir).ok()?;
+    Some(rel.to_path_buf())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_escape_command() {
+        let args = vec!["foo".into(), "bar baz".into(), "weird&stuff".into()];
+        let cmdline = escape_command(&args);
+        assert_eq!(cmdline, "foo 'bar baz' 'weird&stuff'");
+    }
+
+    #[test]
+    fn test_strip_bash_lc_and_escape() {
+        // Test bash
+        let args = vec!["bash".into(), "-lc".into(), "echo hello".into()];
+        let cmdline = strip_bash_lc_and_escape(&args);
+        assert_eq!(cmdline, "echo hello");
+
+        // Test zsh
+        let args = vec!["zsh".into(), "-lc".into(), "echo hello".into()];
+        let cmdline = strip_bash_lc_and_escape(&args);
+        assert_eq!(cmdline, "echo hello");
+
+        // Test absolute path to zsh
+        let args = vec!["/usr/bin/zsh".into(), "-lc".into(), "echo hello".into()];
+        let cmdline = strip_bash_lc_and_escape(&args);
+        assert_eq!(cmdline, "echo hello");
+
+        // Test absolute path to bash
+        let args = vec!["/bin/bash".into(), "-lc".into(), "echo hello".into()];
+        let cmdline = strip_bash_lc_and_escape(&args);
+        assert_eq!(cmdline, "echo hello");
+    }
+}