[connectors] Support connectors part 1 - App server & MCP (#9667)

In order to make Codex work with connectors, we add a built-in gateway
MCP that acts as a transparent proxy between the client and the
connectors. The gateway MCP collects actions that are accessible to the
user and sends them down to the user, when a connector action is chosen
to be called, the client invokes the action through the gateway MCP as
well.

 - [x] Add the system built-in gateway MCP to list and run connectors.
 - [x] Add the app server methods and protocol

codex-rs/app-server/src/codex_message_processor.rs

@@ -13,6 +13,9 @@ use codex_app_server_protocol::AccountLoginCompletedNotification;
 use codex_app_server_protocol::AccountUpdatedNotification;
 use codex_app_server_protocol::AddConversationListenerParams;
 use codex_app_server_protocol::AddConversationSubscriptionResponse;
+use codex_app_server_protocol::AppInfo as ApiAppInfo;
+use codex_app_server_protocol::AppsListParams;
+use codex_app_server_protocol::AppsListResponse;
 use codex_app_server_protocol::ArchiveConversationParams;
 use codex_app_server_protocol::ArchiveConversationResponse;
 use codex_app_server_protocol::AskForApproval;
@@ -122,6 +125,7 @@ use codex_app_server_protocol::UserInput as V2UserInput;
 use codex_app_server_protocol::UserSavedConfig;
 use codex_app_server_protocol::build_turns_from_event_msgs;
 use codex_backend_client::Client as BackendClient;
+use codex_chatgpt::connectors;
 use codex_core::AuthManager;
 use codex_core::CodexThread;
 use codex_core::Cursor as RolloutCursor;
@@ -411,6 +415,9 @@ impl CodexMessageProcessor {
             ClientRequest::SkillsList { request_id, params } => {
                 self.skills_list(request_id, params).await;
             }
+            ClientRequest::AppsList { request_id, params } => {
+                self.apps_list(request_id, params).await;
+            }
             ClientRequest::SkillsConfigWrite { request_id, params } => {
                 self.skills_config_write(request_id, params).await;
             }
@@ -3406,6 +3413,102 @@ impl CodexMessageProcessor {
             .await;
     }
 
+    async fn apps_list(&self, request_id: RequestId, params: AppsListParams) {
+        let AppsListParams { cursor, limit } = params;
+        let config = match self.load_latest_config().await {
+            Ok(config) => config,
+            Err(error) => {
+                self.outgoing.send_error(request_id, error).await;
+                return;
+            }
+        };
+
+        if !config.features.enabled(Feature::Connectors) {
+            self.outgoing
+                .send_response(
+                    request_id,
+                    AppsListResponse {
+                        data: Vec::new(),
+                        next_cursor: None,
+                    },
+                )
+                .await;
+            return;
+        }
+
+        let connectors = match connectors::list_connectors(&config).await {
+            Ok(connectors) => connectors,
+            Err(err) => {
+                self.send_internal_error(request_id, format!("failed to list apps: {err}"))
+                    .await;
+                return;
+            }
+        };
+
+        let total = connectors.len();
+        if total == 0 {
+            self.outgoing
+                .send_response(
+                    request_id,
+                    AppsListResponse {
+                        data: Vec::new(),
+                        next_cursor: None,
+                    },
+                )
+                .await;
+            return;
+        }
+
+        let effective_limit = limit.unwrap_or(total as u32).max(1) as usize;
+        let effective_limit = effective_limit.min(total);
+        let start = match cursor {
+            Some(cursor) => match cursor.parse::<usize>() {
+                Ok(idx) => idx,
+                Err(_) => {
+                    self.send_invalid_request_error(
+                        request_id,
+                        format!("invalid cursor: {cursor}"),
+                    )
+                    .await;
+                    return;
+                }
+            },
+            None => 0,
+        };
+
+        if start > total {
+            self.send_invalid_request_error(
+                request_id,
+                format!("cursor {start} exceeds total apps {total}"),
+            )
+            .await;
+            return;
+        }
+
+        let end = start.saturating_add(effective_limit).min(total);
+        let data = connectors[start..end]
+            .iter()
+            .cloned()
+            .map(|connector| ApiAppInfo {
+                id: connector.connector_id,
+                name: connector.connector_name,
+                description: connector.connector_description,
+                logo_url: connector.logo_url,
+                install_url: connector.install_url,
+                is_accessible: connector.is_accessible,
+            })
+            .collect();
+
+        let next_cursor = if end < total {
+            Some(end.to_string())
+        } else {
+            None
+        };
+        self.outgoing
+            .send_response(request_id, AppsListResponse { data, next_cursor })
+            .await;
+    }
+
     async fn skills_list(&self, request_id: RequestId, params: SkillsListParams) {
         let SkillsListParams { cwds, force_reload } = params;
         let cwds = if cwds.is_empty() {