Allow naming sessions with /new and /clear (#34605)

## What changed

- Accept an optional session name after `/new` or `/clear`.
- Set the requested name through the app server when starting the new thread and update the attached session with that name.
- Report naming failures in the chat while still attaching the newly created thread.

## Testing

- Cover named `/new` and `/clear` dispatch, app-server name persistence, and the existing unnamed `/clear` behavior.

GitOrigin-RevId: 570886abb4af522123f0693ce05d2415e1c0d902

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

@@ -171,7 +171,7 @@ impl ChatWidget {
                 self.request_redraw();
             }
             SlashCommand::New => {
-                self.app_event_tx.send(AppEvent::NewSession);
+                self.app_event_tx.send(AppEvent::NewSession { name: None });
             }
             SlashCommand::Archive => {
                 self.bottom_pane.show_selection_view(SelectionViewParams {
@@ -231,7 +231,7 @@ impl ChatWidget {
                 self.request_redraw();
             }
             SlashCommand::Clear => {
-                self.app_event_tx.send(AppEvent::ClearUi);
+                self.app_event_tx.send(AppEvent::ClearUi { name: None });
             }
             SlashCommand::Resume => {
                 self.app_event_tx.send(AppEvent::OpenResumePicker);
@@ -725,6 +725,16 @@ impl ChatWidget {
                 };
                 self.app_event_tx.set_thread_name(name);
             }
+            SlashCommand::New if !trimmed.is_empty() => {
+                self.app_event_tx.send(AppEvent::NewSession {
+                    name: Some(trimmed.to_string()),
+                });
+            }
+            SlashCommand::Clear if !trimmed.is_empty() => {
+                self.app_event_tx.send(AppEvent::ClearUi {
+                    name: Some(trimmed.to_string()),
+                });
+            }
             SlashCommand::Plan if !trimmed.is_empty() => {
                 if !self.apply_plan_slash_command() {
                     return;