[app-server & core] introduce new codex error code and v2 app-server error events (#6938)

This PR does two things:
1. populate a new `codex_error_code` protocol in error events sent from
core to client;
2. old v1 core events `codex/event/stream_error` and `codex/event/error`
will now both become `error`. We also show codex error code for
turncompleted -> error status.

new events in app server test:
```
< {
<   "method": "codex/event/stream_error",
<   "params": {
<     "conversationId": "019aa34c-0c14-70e0-9706-98520a760d67",
<     "id": "0",
<     "msg": {
<       "codex_error_code": {
<         "response_stream_disconnected": {
<           "http_status_code": 401
<         }
<       },
<       "message": "Reconnecting... 2/5",
<       "type": "stream_error"
<     }
<   }
< }

 {
<   "method": "error",
<   "params": {
<     "error": {
<       "codexErrorCode": {
<         "responseStreamDisconnected": {
<           "httpStatusCode": 401
<         }
<       },
<       "message": "Reconnecting... 2/5"
<     }
<   }
< }

< {
<   "method": "turn/completed",
<   "params": {
<     "turn": {
<       "error": {
<         "codexErrorCode": {
<           "responseTooManyFailedAttempts": {
<             "httpStatusCode": 401
<           }
<         },
<         "message": "exceeded retry limit, last status: 401 Unauthorized, request id: 9a1b495a1a97ed3e-SJC"
<       },
<       "id": "0",
<       "items": [],
<       "status": "failed"
<     }
<   }
< }
```

codex-rs/tui/src/chatwidget.rs

@@ -1664,7 +1664,7 @@ impl ChatWidget {
                 self.on_rate_limit_snapshot(ev.rate_limits);
             }
             EventMsg::Warning(WarningEvent { message }) => self.on_warning(message),
-            EventMsg::Error(ErrorEvent { message }) => self.on_error(message),
+            EventMsg::Error(ErrorEvent { message, .. }) => self.on_error(message),
             EventMsg::McpStartupUpdate(ev) => self.on_mcp_startup_update(ev),
             EventMsg::McpStartupComplete(ev) => self.on_mcp_startup_complete(ev),
             EventMsg::TurnAborted(ev) => match ev.reason {
@@ -1707,7 +1707,9 @@ impl ChatWidget {
             }
             EventMsg::UndoStarted(ev) => self.on_undo_started(ev),
             EventMsg::UndoCompleted(ev) => self.on_undo_completed(ev),
-            EventMsg::StreamError(StreamErrorEvent { message }) => self.on_stream_error(message),
+            EventMsg::StreamError(StreamErrorEvent { message, .. }) => {
+                self.on_stream_error(message)
+            }
             EventMsg::UserMessage(ev) => {
                 if from_replay {
                     self.on_user_message_event(ev);

codex-rs/tui/src/chatwidget/agent.rs

@@ -4,7 +4,6 @@ use codex_core::CodexConversation;
 use codex_core::ConversationManager;
 use codex_core::NewConversation;
 use codex_core::config::Config;
-use codex_core::protocol::ErrorEvent;
 use codex_core::protocol::Event;
 use codex_core::protocol::EventMsg;
 use codex_core::protocol::Op;
@@ -37,7 +36,7 @@ pub(crate) fn spawn_agent(
                 eprintln!("{message}");
                 app_event_tx_clone.send(AppEvent::CodexEvent(Event {
                     id: "".to_string(),
-                    msg: EventMsg::Error(ErrorEvent { message }),
+                    msg: EventMsg::Error(err.to_error_event(None)),
                 }));
                 app_event_tx_clone.send(AppEvent::ExitRequest);
                 tracing::error!("failed to initialize codex: {err}");

codex-rs/tui/src/chatwidget/tests.rs

@@ -50,6 +50,7 @@ use codex_protocol::parse_command::ParsedCommand;
 use codex_protocol::plan_tool::PlanItemArg;
 use codex_protocol::plan_tool::StepStatus;
 use codex_protocol::plan_tool::UpdatePlanArgs;
+use codex_protocol::protocol::CodexErrorInfo;
 use crossterm::event::KeyCode;
 use crossterm::event::KeyEvent;
 use crossterm::event::KeyModifiers;
@@ -2647,6 +2648,7 @@ fn stream_error_updates_status_indicator() {
         id: "sub-1".into(),
         msg: EventMsg::StreamError(StreamErrorEvent {
             message: msg.to_string(),
+            codex_error_code: Some(CodexErrorInfo::Other),
         }),
     });