Add temporary app-server originator fallback for codex-tui (#15218)

## Summary
- make app-server treat `clientInfo.name == "codex-tui"` as a legacy
compatibility case
- fall back to `DEFAULT_ORIGINATOR` instead of sending `codex-tui` as
the originator header
- add a TODO noting this is a temporary workaround that should be
removed later

## Testing
- Not run (not requested)

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

@@ -53,6 +53,7 @@ use codex_core::ThreadManager;
 use codex_core::config::Config;
 use codex_core::config_loader::CloudRequirementsLoader;
 use codex_core::config_loader::LoaderOverrides;
+use codex_core::default_client::DEFAULT_ORIGINATOR;
 use codex_core::default_client::SetOriginatorError;
 use codex_core::default_client::USER_AGENT_SUFFIX;
 use codex_core::default_client::get_codex_user_agent;
@@ -78,6 +79,7 @@ use toml::Value as TomlValue;
 use tracing::Instrument;
 
 const EXTERNAL_AUTH_REFRESH_TIMEOUT: Duration = Duration::from_secs(10);
+const TUI_APP_SERVER_CLIENT_NAME: &str = "codex-tui";
 
 #[derive(Clone)]
 struct ExternalAuthRefreshBridge {
@@ -551,7 +553,14 @@ impl MessageProcessor {
                 } = params.client_info;
                 session.app_server_client_name = Some(name.clone());
                 session.client_version = Some(version.clone());
-                if let Err(error) = set_default_originator(name.clone()) {
+                let originator = if name == TUI_APP_SERVER_CLIENT_NAME {
+                    // TODO: Remove this temporary workaround once app-server clients no longer
+                    // need to retain the legacy TUI `codex_cli_rs` originator behavior.
+                    DEFAULT_ORIGINATOR.to_string()
+                } else {
+                    name.clone()
+                };
+                if let Err(error) = set_default_originator(originator) {
                     match error {
                         SetOriginatorError::InvalidHeaderValue => {
                             let error = JSONRPCErrorError {