feat: initial import of Rust implementation of Codex CLI in codex-rs/ (#629)

As stated in `codex-rs/README.md`:

Today, Codex CLI is written in TypeScript and requires Node.js 22+ to
run it. For a number of users, this runtime requirement inhibits
adoption: they would be better served by a standalone executable. As
maintainers, we want Codex to run efficiently in a wide range of
environments with minimal overhead. We also want to take advantage of
operating system-specific APIs to provide better sandboxing, where
possible.

To that end, we are moving forward with a Rust implementation of Codex
CLI contained in this folder, which has the following benefits:

- The CLI compiles to small, standalone, platform-specific binaries.
- Can make direct, native calls to
[seccomp](https://man7.org/linux/man-pages/man2/seccomp.2.html) and
[landlock](https://man7.org/linux/man-pages/man7/landlock.7.html) in
order to support sandboxing on Linux.
- No runtime garbage collection, resulting in lower memory consumption
and better, more predictable performance.

Currently, the Rust implementation is materially behind the TypeScript
implementation in functionality, so continue to use the TypeScript
implmentation for the time being. We will publish native executables via
GitHub Releases as soon as we feel the Rust version is usable.

codex-rs/repl/src/cli.rs

@@ -0,0 +1,60 @@
+use clap::ArgAction;
+use clap::Parser;
+use codex_core::ApprovalModeCliArg;
+use codex_core::SandboxModeCliArg;
+use std::path::PathBuf;
+
+/// Command‑line arguments.
+#[derive(Debug, Parser)]
+#[command(
+    author,
+    version,
+    about = "Interactive Codex CLI that streams all agent actions."
+)]
+pub struct Cli {
+    /// User prompt to start the session.
+    pub prompt: Option<String>,
+
+    /// Override the default model from ~/.codex/config.toml.
+    #[arg(short, long)]
+    pub model: Option<String>,
+
+    /// Optional images to attach to the prompt.
+    #[arg(long, value_name = "FILE")]
+    pub images: Vec<PathBuf>,
+
+    /// Increase verbosity (-v info, -vv debug, -vvv trace).
+    ///
+    /// The flag may be passed up to three times. Without any -v the CLI only prints warnings and errors.
+    #[arg(short, long, action = ArgAction::Count)]
+    pub verbose: u8,
+
+    /// Don't use colored ansi output for verbose logging
+    #[arg(long)]
+    pub no_ansi: bool,
+
+    /// Configure when the model requires human approval before executing a command.
+    #[arg(long = "ask-for-approval", short = 'a', value_enum, default_value_t = ApprovalModeCliArg::OnFailure)]
+    pub approval_policy: ApprovalModeCliArg,
+
+    /// Configure the process restrictions when a command is executed.
+    ///
+    /// Uses OS-specific sandboxing tools; Seatbelt on OSX, landlock+seccomp on Linux.
+    #[arg(long = "sandbox", short = 's', value_enum, default_value_t = SandboxModeCliArg::NetworkAndFileWriteRestricted)]
+    pub sandbox_policy: SandboxModeCliArg,
+
+    /// Allow running Codex outside a Git repository.  By default the CLI
+    /// aborts early when the current working directory is **not** inside a
+    /// Git repo because most agents rely on `git` for interacting with the
+    /// code‑base.  Pass this flag if you really know what you are doing.
+    #[arg(long, action = ArgAction::SetTrue, default_value_t = false)]
+    pub allow_no_git_exec: bool,
+
+    /// Record submissions into file as JSON
+    #[arg(short = 'S', long)]
+    pub record_submissions: Option<String>,
+
+    /// Record events into file as JSON
+    #[arg(short = 'E', long)]
+    pub record_events: Option<String>,
+}