Add codex apply to apply a patch created from the Codex remote agent (#1528)

In order to to this, I created a new `chatgpt` crate where we can put
any code that interacts directly with ChatGPT as opposed to the OpenAI
API. I added a disclaimer to the README for it that it should primarily
be modified by OpenAI employees.


https://github.com/user-attachments/assets/bb978e33-d2c9-4d8e-af28-c8c25b1988e8

codex-rs/chatgpt/src/apply_command.rs

@@ -0,0 +1,89 @@
+use clap::Parser;
+use codex_common::CliConfigOverrides;
+use codex_core::config::Config;
+use codex_core::config::ConfigOverrides;
+
+use crate::chatgpt_token::init_chatgpt_token_from_auth;
+use crate::get_task::GetTaskResponse;
+use crate::get_task::OutputItem;
+use crate::get_task::PrOutputItem;
+use crate::get_task::get_task;
+
+/// Applies the latest diff from a Codex agent task.
+#[derive(Debug, Parser)]
+pub struct ApplyCommand {
+    pub task_id: String,
+
+    #[clap(flatten)]
+    pub config_overrides: CliConfigOverrides,
+}
+pub async fn run_apply_command(apply_cli: ApplyCommand) -> anyhow::Result<()> {
+    let config = Config::load_with_cli_overrides(
+        apply_cli
+            .config_overrides
+            .parse_overrides()
+            .map_err(anyhow::Error::msg)?,
+        ConfigOverrides::default(),
+    )?;
+
+    init_chatgpt_token_from_auth(&config.codex_home).await?;
+
+    let task_response = get_task(&config, apply_cli.task_id).await?;
+    apply_diff_from_task(task_response).await
+}
+
+pub async fn apply_diff_from_task(task_response: GetTaskResponse) -> anyhow::Result<()> {
+    let diff_turn = match task_response.current_diff_task_turn {
+        Some(turn) => turn,
+        None => anyhow::bail!("No diff turn found"),
+    };
+    let output_diff = diff_turn.output_items.iter().find_map(|item| match item {
+        OutputItem::Pr(PrOutputItem { output_diff }) => Some(output_diff),
+        _ => None,
+    });
+    match output_diff {
+        Some(output_diff) => apply_diff(&output_diff.diff).await,
+        None => anyhow::bail!("No PR output item found"),
+    }
+}
+
+async fn apply_diff(diff: &str) -> anyhow::Result<()> {
+    let toplevel_output = tokio::process::Command::new("git")
+        .args(vec!["rev-parse", "--show-toplevel"])
+        .output()
+        .await?;
+
+    if !toplevel_output.status.success() {
+        anyhow::bail!("apply must be run from a git repository.");
+    }
+
+    let repo_root = String::from_utf8(toplevel_output.stdout)?
+        .trim()
+        .to_string();
+
+    let mut git_apply_cmd = tokio::process::Command::new("git")
+        .args(vec!["apply", "--3way"])
+        .current_dir(&repo_root)
+        .stdin(std::process::Stdio::piped())
+        .stdout(std::process::Stdio::piped())
+        .stderr(std::process::Stdio::piped())
+        .spawn()?;
+
+    if let Some(mut stdin) = git_apply_cmd.stdin.take() {
+        tokio::io::AsyncWriteExt::write_all(&mut stdin, diff.as_bytes()).await?;
+        drop(stdin);
+    }
+
+    let output = git_apply_cmd.wait_with_output().await?;
+
+    if !output.status.success() {
+        anyhow::bail!(
+            "Git apply failed with status {}: {}",
+            output.status,
+            String::from_utf8_lossy(&output.stderr)
+        );
+    }
+
+    println!("Successfully applied diff");
+    Ok(())
+}