feat(app-server) Expose personality (#9674)

### Motivation
Exposes a per-thread / per-turn `personality` override in the v2
app-server API so clients can influence model communication style at
thread/turn start. Ensures the override is passed into the session
configuration resolution so it becomes effective for subsequent turns
and headless runners.

### Testing
- [x] Add an integration-style test
`turn_start_accepts_personality_override_v2` in
`codex-rs/app-server/tests/suite/v2/turn_start.rs` that verifies a
`/personality` override results in a developer update message containing
`<personality_spec>` in the outbound model request.

------
[Codex
Task](https://chatgpt.com/codex/tasks/task_i_6971d646b1c08322a689a54d2649f3fe)

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

@@ -11,18 +11,23 @@ use codex_app_server_protocol::ThreadResumeParams;
 use codex_app_server_protocol::ThreadResumeResponse;
 use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
+use codex_app_server_protocol::TurnStartParams;
 use codex_app_server_protocol::TurnStatus;
 use codex_app_server_protocol::UserInput;
+use codex_protocol::config_types::Personality;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::user_input::ByteRange;
 use codex_protocol::user_input::TextElement;
+use core_test_support::responses;
+use core_test_support::skip_if_no_network;
 use pretty_assertions::assert_eq;
 use std::path::PathBuf;
 use tempfile::TempDir;
 use tokio::time::timeout;
 
 const DEFAULT_READ_TIMEOUT: std::time::Duration = std::time::Duration::from_secs(10);
+const DEFAULT_BASE_INSTRUCTIONS: &str = "You are Codex, based on GPT-5. You are running as a coding agent in the Codex CLI on a user's computer.";
 
 #[tokio::test]
 async fn thread_resume_returns_original_thread() -> Result<()> {
@@ -248,6 +253,91 @@ async fn thread_resume_supports_history_and_overrides() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn thread_resume_accepts_personality_override_v2() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let body = responses::sse(vec![
+        responses::ev_response_created("resp-1"),
+        responses::ev_assistant_message("msg-1", "Done"),
+        responses::ev_completed("resp-1"),
+    ]);
+    let response_mock = responses::mount_sse_once(&server, body).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("gpt-5.2-codex".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 resume_id = mcp
+        .send_thread_resume_request(ThreadResumeParams {
+            thread_id: thread.id.clone(),
+            model: Some("gpt-5.2-codex".to_string()),
+            personality: Some(Personality::Friendly),
+            ..Default::default()
+        })
+        .await?;
+    let resume_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(resume_id)),
+    )
+    .await??;
+    let _resume: ThreadResumeResponse = to_response::<ThreadResumeResponse>(resume_resp)?;
+
+    let turn_id = mcp
+        .send_turn_start_request(TurnStartParams {
+            thread_id: thread.id,
+            input: vec![UserInput::Text {
+                text: "Hello".to_string(),
+                text_elements: Vec::new(),
+            }],
+            ..Default::default()
+        })
+        .await?;
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(turn_id)),
+    )
+    .await??;
+
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+
+    let request = response_mock.single_request();
+    let developer_texts = request.message_input_texts("developer");
+    assert!(
+        !developer_texts
+            .iter()
+            .any(|text| text.contains("<personality_spec>")),
+        "did not expect a personality update message in developer input, got {developer_texts:?}"
+    );
+    let instructions_text = request.instructions_text();
+    assert!(
+        instructions_text.contains(DEFAULT_BASE_INSTRUCTIONS),
+        "expected default base instructions from history, got {instructions_text:?}"
+    );
+
+    Ok(())
+}
+
 // Helper to create a config.toml pointing at the mock model server.
 fn create_config_toml(codex_home: &std::path::Path, server_uri: &str) -> std::io::Result<()> {
     let config_toml = codex_home.join("config.toml");
@@ -261,6 +351,9 @@ sandbox_mode = "read-only"
 
 model_provider = "mock_provider"
 
+[features]
+remote_models = false
+
 [model_providers.mock_provider]
 name = "Mock provider for test"
 base_url = "{server_uri}/v1"

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

@@ -34,13 +34,17 @@ use codex_app_server_protocol::TurnStartResponse;
 use codex_app_server_protocol::TurnStartedNotification;
 use codex_app_server_protocol::TurnStatus;
 use codex_app_server_protocol::UserInput as V2UserInput;
+use codex_core::features::FEATURES;
+use codex_core::features::Feature;
 use codex_core::protocol_config_types::ReasoningSummary;
 use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::Settings;
 use codex_protocol::openai_models::ReasoningEffort;
 use core_test_support::responses;
 use core_test_support::skip_if_no_network;
 use pretty_assertions::assert_eq;
+use std::collections::BTreeMap;
 use std::path::Path;
 use tempfile::TempDir;
 use tokio::time::timeout;
@@ -54,7 +58,12 @@ async fn turn_start_sends_originator_header() -> Result<()> {
     let server = create_mock_responses_server_sequence_unchecked(responses).await;
 
     let codex_home = TempDir::new()?;
-    create_config_toml(codex_home.path(), &server.uri(), "never")?;
+    create_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.path()).await?;
     timeout(
@@ -124,7 +133,12 @@ async fn turn_start_emits_user_message_item_with_text_elements() -> Result<()> {
     let server = create_mock_responses_server_sequence_unchecked(responses).await;
 
     let codex_home = TempDir::new()?;
-    create_config_toml(codex_home.path(), &server.uri(), "never")?;
+    create_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -211,7 +225,12 @@ async fn turn_start_emits_notifications_and_accepts_model_override() -> Result<(
     let server = create_mock_responses_server_sequence_unchecked(responses).await;
 
     let codex_home = TempDir::new()?;
-    create_config_toml(codex_home.path(), &server.uri(), "never")?;
+    create_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -321,13 +340,19 @@ async fn turn_start_accepts_collaboration_mode_override_v2() -> Result<()> {
     let response_mock = responses::mount_sse_once(&server, body).await;
 
     let codex_home = TempDir::new()?;
-    create_config_toml(codex_home.path(), &server.uri(), "never")?;
+    create_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
 
     let thread_req = mcp
         .send_thread_start_request(ThreadStartParams {
+            model: Some("gpt-5.2-codex".to_string()),
             ..Default::default()
         })
         .await?;
@@ -379,6 +404,81 @@ async fn turn_start_accepts_collaboration_mode_override_v2() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn turn_start_accepts_personality_override_v2() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let body = responses::sse(vec![
+        responses::ev_response_created("resp-1"),
+        responses::ev_assistant_message("msg-1", "Done"),
+        responses::ev_completed("resp-1"),
+    ]);
+    let response_mock = responses::mount_sse_once(&server, body).await;
+
+    let codex_home = TempDir::new()?;
+    create_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &BTreeMap::default(),
+    )?;
+
+    let mut mcp = McpProcess::new(codex_home.path()).await?;
+    timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
+
+    let thread_req = mcp
+        .send_thread_start_request(ThreadStartParams {
+            model: Some("gpt-5.2-codex".to_string()),
+            ..Default::default()
+        })
+        .await?;
+    let thread_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(thread_req)),
+    )
+    .await??;
+    let ThreadStartResponse { thread, .. } = to_response::<ThreadStartResponse>(thread_resp)?;
+
+    let turn_req = mcp
+        .send_turn_start_request(TurnStartParams {
+            thread_id: thread.id.clone(),
+            input: vec![V2UserInput::Text {
+                text: "Hello".to_string(),
+                text_elements: Vec::new(),
+            }],
+            personality: Some(Personality::Friendly),
+            ..Default::default()
+        })
+        .await?;
+    let turn_resp: JSONRPCResponse = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_response_message(RequestId::Integer(turn_req)),
+    )
+    .await??;
+    let _turn: TurnStartResponse = to_response::<TurnStartResponse>(turn_resp)?;
+
+    timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("turn/completed"),
+    )
+    .await??;
+
+    let request = response_mock.single_request();
+    let developer_texts = request.message_input_texts("developer");
+    if developer_texts.is_empty() {
+        eprintln!("request body: {}", request.body_json());
+    }
+    assert!(
+        developer_texts
+            .iter()
+            .any(|text| text.contains("<personality_spec>")),
+        "expected personality update message in developer input, got {developer_texts:?}"
+    );
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn turn_start_accepts_local_image_input() -> Result<()> {
     // Two Codex turns hit the mock model (session start + turn/start).
@@ -391,7 +491,12 @@ async fn turn_start_accepts_local_image_input() -> Result<()> {
     let server = create_mock_responses_server_sequence_unchecked(responses).await;
 
     let codex_home = TempDir::new()?;
-    create_config_toml(codex_home.path(), &server.uri(), "never")?;
+    create_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -466,7 +571,12 @@ async fn turn_start_exec_approval_toggle_v2() -> Result<()> {
     ];
     let server = create_mock_responses_server_sequence(responses).await;
     // Default approval is untrusted to force elicitation on first turn.
-    create_config_toml(codex_home.as_path(), &server.uri(), "untrusted")?;
+    create_config_toml(
+        codex_home.as_path(),
+        &server.uri(),
+        "untrusted",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.as_path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -591,7 +701,12 @@ async fn turn_start_exec_approval_decline_v2() -> Result<()> {
         create_final_assistant_message_sse_response("done")?,
     ];
     let server = create_mock_responses_server_sequence(responses).await;
-    create_config_toml(codex_home.as_path(), &server.uri(), "untrusted")?;
+    create_config_toml(
+        codex_home.as_path(),
+        &server.uri(),
+        "untrusted",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.as_path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -738,7 +853,12 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
         create_final_assistant_message_sse_response("done second")?,
     ];
     let server = create_mock_responses_server_sequence(responses).await;
-    create_config_toml(&codex_home, &server.uri(), "untrusted")?;
+    create_config_toml(
+        &codex_home,
+        &server.uri(),
+        "untrusted",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(&codex_home).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -776,6 +896,7 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
             model: Some("mock-model".to_string()),
             effort: Some(ReasoningEffort::Medium),
             summary: Some(ReasoningSummary::Auto),
+            personality: None,
             output_schema: None,
             collaboration_mode: None,
         })
@@ -806,6 +927,7 @@ async fn turn_start_updates_sandbox_and_cwd_between_turns_v2() -> Result<()> {
             model: Some("mock-model".to_string()),
             effort: Some(ReasoningEffort::Medium),
             summary: Some(ReasoningSummary::Auto),
+            personality: None,
             output_schema: None,
             collaboration_mode: None,
         })
@@ -876,7 +998,12 @@ async fn turn_start_file_change_approval_v2() -> Result<()> {
         create_final_assistant_message_sse_response("patch applied")?,
     ];
     let server = create_mock_responses_server_sequence(responses).await;
-    create_config_toml(&codex_home, &server.uri(), "untrusted")?;
+    create_config_toml(
+        &codex_home,
+        &server.uri(),
+        "untrusted",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(&codex_home).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -1053,7 +1180,12 @@ async fn turn_start_file_change_approval_accept_for_session_persists_v2() -> Res
         create_final_assistant_message_sse_response("patch 2 applied")?,
     ];
     let server = create_mock_responses_server_sequence(responses).await;
-    create_config_toml(&codex_home, &server.uri(), "untrusted")?;
+    create_config_toml(
+        &codex_home,
+        &server.uri(),
+        "untrusted",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(&codex_home).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -1229,7 +1361,12 @@ async fn turn_start_file_change_approval_decline_v2() -> Result<()> {
         create_final_assistant_message_sse_response("patch declined")?,
     ];
     let server = create_mock_responses_server_sequence(responses).await;
-    create_config_toml(&codex_home, &server.uri(), "untrusted")?;
+    create_config_toml(
+        &codex_home,
+        &server.uri(),
+        "untrusted",
+        &BTreeMap::default(),
+    )?;
 
     let mut mcp = McpProcess::new(&codex_home).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -1369,16 +1506,12 @@ async fn command_execution_notifications_include_process_id() -> Result<()> {
     ];
     let server = create_mock_responses_server_sequence(responses).await;
     let codex_home = TempDir::new()?;
-    create_config_toml(codex_home.path(), &server.uri(), "never")?;
-    let config_toml = codex_home.path().join("config.toml");
-    let mut config_contents = std::fs::read_to_string(&config_toml)?;
-    config_contents.push_str(
-        r#"
-[features]
-unified_exec = true
-"#,
-    );
-    std::fs::write(&config_toml, config_contents)?;
+    create_config_toml(
+        codex_home.path(),
+        &server.uri(),
+        "never",
+        &BTreeMap::from([(Feature::UnifiedExec, true)]),
+    )?;
 
     let mut mcp = McpProcess::new(codex_home.path()).await?;
     timeout(DEFAULT_READ_TIMEOUT, mcp.initialize()).await??;
@@ -1502,7 +1635,24 @@ fn create_config_toml(
     codex_home: &Path,
     server_uri: &str,
     approval_policy: &str,
+    feature_flags: &BTreeMap<Feature, bool>,
 ) -> std::io::Result<()> {
+    let mut features = BTreeMap::from([(Feature::RemoteModels, false)]);
+    for (feature, enabled) in feature_flags {
+        features.insert(*feature, *enabled);
+    }
+    let feature_entries = features
+        .into_iter()
+        .map(|(feature, enabled)| {
+            let key = FEATURES
+                .iter()
+                .find(|spec| spec.id == feature)
+                .map(|spec| spec.key)
+                .unwrap_or_else(|| panic!("missing feature key for {feature:?}"));
+            format!("{key} = {enabled}")
+        })
+        .collect::<Vec<_>>()
+        .join("\n");
     let config_toml = codex_home.join("config.toml");
     std::fs::write(
         config_toml,
@@ -1514,6 +1664,9 @@ sandbox_mode = "read-only"
 
 model_provider = "mock_provider"
 
+[features]
+{feature_entries}
+
 [model_providers.mock_provider]
 name = "Mock provider for test"
 base_url = "{server_uri}/v1"