Move TUI on top of app server (parallel code) (#14717)

This PR replicates the `tui` code directory and creates a temporary
parallel `tui_app_server` directory. It also implements a new feature
flag `tui_app_server` to select between the two tui implementations.

Once the new app-server-based TUI is stabilized, we'll delete the old
`tui` directory and feature flag.

codex-rs/tui_app_server/src/app_event_sender.rs

@@ -0,0 +1,123 @@
+use std::path::PathBuf;
+
+use crate::app_command::AppCommand;
+use codex_protocol::ThreadId;
+use codex_protocol::approvals::ElicitationAction;
+use codex_protocol::mcp::RequestId as McpRequestId;
+use codex_protocol::protocol::ConversationAudioParams;
+use codex_protocol::protocol::ReviewDecision;
+use codex_protocol::protocol::ReviewRequest;
+use codex_protocol::request_permissions::RequestPermissionsResponse;
+use codex_protocol::request_user_input::RequestUserInputResponse;
+use tokio::sync::mpsc::UnboundedSender;
+
+use crate::app_event::AppEvent;
+use crate::session_log;
+
+#[derive(Clone, Debug)]
+pub(crate) struct AppEventSender {
+    pub app_event_tx: UnboundedSender<AppEvent>,
+}
+
+impl AppEventSender {
+    pub(crate) fn new(app_event_tx: UnboundedSender<AppEvent>) -> Self {
+        Self { app_event_tx }
+    }
+
+    /// Send an event to the app event channel. If it fails, we swallow the
+    /// error and log it.
+    pub(crate) fn send(&self, event: AppEvent) {
+        // Record inbound events for high-fidelity session replay.
+        // Avoid double-logging Ops; those are logged at the point of submission.
+        if !matches!(event, AppEvent::CodexOp(_)) {
+            session_log::log_inbound_app_event(&event);
+        }
+        if let Err(e) = self.app_event_tx.send(event) {
+            tracing::error!("failed to send event: {e}");
+        }
+    }
+
+    pub(crate) fn interrupt(&self) {
+        self.send(AppEvent::CodexOp(AppCommand::interrupt().into_core()));
+    }
+
+    pub(crate) fn compact(&self) {
+        self.send(AppEvent::CodexOp(AppCommand::compact().into_core()));
+    }
+
+    pub(crate) fn set_thread_name(&self, name: String) {
+        self.send(AppEvent::CodexOp(
+            AppCommand::set_thread_name(name).into_core(),
+        ));
+    }
+
+    pub(crate) fn review(&self, review_request: ReviewRequest) {
+        self.send(AppEvent::CodexOp(
+            AppCommand::review(review_request).into_core(),
+        ));
+    }
+
+    pub(crate) fn list_skills(&self, cwds: Vec<PathBuf>, force_reload: bool) {
+        self.send(AppEvent::CodexOp(
+            AppCommand::list_skills(cwds, force_reload).into_core(),
+        ));
+    }
+
+    #[cfg_attr(
+        any(target_os = "linux", not(feature = "voice-input")),
+        allow(dead_code)
+    )]
+    pub(crate) fn realtime_conversation_audio(&self, params: ConversationAudioParams) {
+        self.send(AppEvent::CodexOp(
+            AppCommand::realtime_conversation_audio(params).into_core(),
+        ));
+    }
+
+    pub(crate) fn user_input_answer(&self, id: String, response: RequestUserInputResponse) {
+        self.send(AppEvent::CodexOp(
+            AppCommand::user_input_answer(id, response).into_core(),
+        ));
+    }
+
+    pub(crate) fn exec_approval(&self, thread_id: ThreadId, id: String, decision: ReviewDecision) {
+        self.send(AppEvent::SubmitThreadOp {
+            thread_id,
+            op: AppCommand::exec_approval(id, None, decision).into_core(),
+        });
+    }
+
+    pub(crate) fn request_permissions_response(
+        &self,
+        thread_id: ThreadId,
+        id: String,
+        response: RequestPermissionsResponse,
+    ) {
+        self.send(AppEvent::SubmitThreadOp {
+            thread_id,
+            op: AppCommand::request_permissions_response(id, response).into_core(),
+        });
+    }
+
+    pub(crate) fn patch_approval(&self, thread_id: ThreadId, id: String, decision: ReviewDecision) {
+        self.send(AppEvent::SubmitThreadOp {
+            thread_id,
+            op: AppCommand::patch_approval(id, decision).into_core(),
+        });
+    }
+
+    pub(crate) fn resolve_elicitation(
+        &self,
+        thread_id: ThreadId,
+        server_name: String,
+        request_id: McpRequestId,
+        decision: ElicitationAction,
+        content: Option<serde_json::Value>,
+        meta: Option<serde_json::Value>,
+    ) {
+        self.send(AppEvent::SubmitThreadOp {
+            thread_id,
+            op: AppCommand::resolve_elicitation(server_name, request_id, decision, content, meta)
+                .into_core(),
+        });
+    }
+}