codex/codex-rs/app-server/tests/suite/v2/thread_fork.rs

use anyhow::Result;
use app_test_support::McpProcess;
use app_test_support::create_fake_rollout;
use app_test_support::create_mock_responses_server_repeating_assistant;
use app_test_support::to_response;
use codex_app_server_protocol::JSONRPCError;
use codex_app_server_protocol::JSONRPCMessage;
use codex_app_server_protocol::JSONRPCResponse;
use codex_app_server_protocol::RequestId;
use codex_app_server_protocol::SessionSource;
use codex_app_server_protocol::ThreadForkParams;
use codex_app_server_protocol::ThreadForkResponse;
use codex_app_server_protocol::ThreadItem;
use codex_app_server_protocol::ThreadStartParams;
use codex_app_server_protocol::ThreadStartResponse;
use codex_app_server_protocol::ThreadStartedNotification;
use codex_app_server_protocol::ThreadStatus;
use codex_app_server_protocol::ThreadStatusChangedNotification;
use codex_app_server_protocol::TurnStatus;
use codex_app_server_protocol::UserInput;
use pretty_assertions::assert_eq;
use serde_json::Value;
use std::path::Path;
use tempfile::TempDir;
use tokio::time::timeout;

const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);

#[tokio::test]
async fn thread_fork_creates_new_thread_and_emits_started() -> Result<()> {
    let server = create_mock_responses_server_repeating_assistant("Done").await;
    let codex_home = TempDir::new()?;
    create_config_toml(codex_home.path(), &server.uri())?;

    let preview = "Saved user message";
    let conversation_id = create_fake_rollout(
        codex_home.path(),
        "2025-01-05T12-00-00",
        "2025-01-05T12:00:00Z",
        preview,
        Some("mock_provider"),
        None,
    )?;

    let original_path = codex_home
        .path()
        .join("sessions")
        .join("2025")
        .join("01")
        .join("05")
        .join(format!(
            "rollout-2025-01-05T12-00-00-{conversation_id}.jsonl"
        ));
    assert!(
        original_path.exists(),
        "expected original rollout to exist at {}",
        original_path.display()
    );
    let original_contents = std::fs::read_to_string(&original_path)?;

    let mut mcp = McpProcess::new(codex_home.path()).await?;
    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;

    let fork_id = mcp
        .send_thread_fork_request(ThreadForkParams {
            thread_id: conversation_id.clone(),
            ..Default::default()
        })
        .await?;
    let fork_resp: JSONRPCResponse = timeout(
        DEFAULT_READ_TIMEOUT,
        mcp.read_stream_until_response_message(RequestId::Integer(fork_id)),
    )
    .await??;
    let fork_result = fork_resp.result.clone();
    let ThreadForkResponse { thread, .. } = to_response::<ThreadForkResponse>(fork_resp)?;

    // Wire contract: thread title field is `name`, serialized as null when unset.
    let thread_json = fork_result
        .get("thread")
        .and_then(Value::as_object)
        .expect("thread/fork result.thread must be an object");
    assert_eq!(
        thread_json.get("name"),
        Some(&Value::Null),
        "forked threads do not inherit a name; expected `name: null`"
    );

    let after_contents = std::fs::read_to_string(&original_path)?;
    assert_eq!(
        after_contents, original_contents,
        "fork should not mutate the original rollout file"
    );

    assert_ne!(thread.id, conversation_id);
    assert_eq!(thread.preview, preview);
    assert_eq!(thread.model_provider, "mock_provider");
    assert_eq!(thread.status, ThreadStatus::Idle);
    let thread_path = thread.path.clone().expect("thread path");
    assert!(thread_path.is_absolute());
    assert_ne!(thread_path, original_path);
    assert!(thread.cwd.is_absolute());
    assert_eq!(thread.source, SessionSource::VsCode);
    assert_eq!(thread.name, None);

    assert_eq!(
        thread.turns.len(),
        1,
        "expected forked thread to include one turn"
    );
    let turn = &thread.turns[0];
    assert_eq!(turn.status, TurnStatus::Completed);
    assert_eq!(turn.items.len(), 1, "expected user message item");
    match &turn.items[0] {
        ThreadItem::UserMessage { content, .. } => {
            assert_eq!(
                content,
                &vec![UserInput::Text {
                    text: preview.to_string(),
                    text_elements: Vec::new(),
                }]
            );
        }
        other => panic!("expected user message item, got {other:?}"),
    }

    // A corresponding thread/started notification should arrive.
    let deadline = tokio::time::Instant::now() + DEFAULT_READ_TIMEOUT;
    let notif = loop {
        let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
        let message = timeout(remaining, mcp.read_next_message()).await??;
        let JSONRPCMessage::Notification(notif) = message else {
            continue;
        };
        if notif.method == "thread/status/changed" {
            let status_changed: ThreadStatusChangedNotification =
                serde_json::from_value(notif.params.expect("params must be present"))?;
            if status_changed.thread_id == thread.id {
                anyhow::bail!(
                    "thread/fork should introduce the thread without a preceding thread/status/changed"
                );
            }
            continue;
        }
        if notif.method == "thread/started" {
            break notif;
        }
    };
    let started_params = notif.params.clone().expect("params must be present");
    let started_thread_json = started_params
        .get("thread")
        .and_then(Value::as_object)
        .expect("thread/started params.thread must be an object");
    assert_eq!(
        started_thread_json.get("name"),
        Some(&Value::Null),
        "thread/started must serialize `name: null` when unset"
    );
    let started: ThreadStartedNotification =
        serde_json::from_value(notif.params.expect("params must be present"))?;
    assert_eq!(started.thread, thread);

    Ok(())
}

#[tokio::test]
async fn thread_fork_rejects_unmaterialized_thread() -> Result<()> {
    let server = create_mock_responses_server_repeating_assistant("Done").await;
    let codex_home = TempDir::new()?;
    create_config_toml(codex_home.path(), &server.uri())?;

    let mut mcp = McpProcess::new(codex_home.path()).await?;
    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;

    let start_id = mcp
        .send_thread_start_request(ThreadStartParams {
            model: Some("mock-model".to_string()),
            ..Default::default()
        })
        .await?;
    let start_resp: JSONRPCResponse = timeout(
        DEFAULT_READ_TIMEOUT,
        mcp.read_stream_until_response_message(RequestId::Integer(start_id)),
    )
    .await??;
    let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(start_resp)?;

    let fork_id = mcp
        .send_thread_fork_request(ThreadForkParams {
            thread_id: thread.id,
            ..Default::default()
        })
        .await?;
    let fork_err: JSONRPCError = timeout(
        DEFAULT_READ_TIMEOUT,
        mcp.read_stream_until_error_message(RequestId::Integer(fork_id)),
    )
    .await??;
    assert!(
        fork_err
            .error
            .message
            .contains("no rollout found for thread id"),
        "unexpected fork error: {}",
        fork_err.error.message
    );

    Ok(())
}

// Helper to create a config.toml pointing at the mock model server.
fn create_config_toml(codex_home: &Path, server_uri: &str) -> std::io::Result<()> {
    let config_toml = codex_home.join("config.toml");
    std::fs::write(
        config_toml,
        format!(
            r#"
model = "mock-model"
approval_policy = "never"
sandbox_mode = "read-only"

model_provider = "mock_provider"

[model_providers.mock_provider]
name = "Mock provider for test"
base_url = "{server_uri}/v1"
wire_api = "responses"
request_max_retries = 0
stream_max_retries = 0
"#
        ),
    )
}