Add a dedicated codex agents dashboard command (#39114)

## What changed

- Add `codex agents` to open the shared agents overview without creating a new session.
- Start the local background app server automatically on Unix, or connect to a server supplied with `--remote`.
- Reject invocation-specific session overrides that cannot apply to shared sessions.
- When the overview is opened from an embedded session, offer to start the background server without moving or interrupting the current session.

## Testing

- Cover command-line parsing and rejection of incompatible overrides.
- Snapshot the embedded-session background-server prompt.

GitOrigin-RevId: 60845dfebc48d820dc4ff090626d30452127f062

codex-rs/tui/src/app/event_dispatch.rs

@@ -191,7 +191,9 @@ impl App {
                             }
                         }
                     }
-                    SessionSelection::Exit | SessionSelection::StartFresh => {
+                    SessionSelection::Exit
+                    | SessionSelection::StartFresh
+                    | SessionSelection::AgentsOverview => {
                         self.refresh_in_memory_config_from_disk_best_effort(
                             "closing the session picker",
                         )
@@ -2326,6 +2328,9 @@ impl App {
                     .select_agents_overview_thread(tui, app_server, thread_id)
                     .await?
                 {
+                    AppRunControl::Continue if self.primary_thread_id.is_none() => {
+                        self.open_agents_overview(app_server);
+                    }
                     AppRunControl::Continue => {}
                     AppRunControl::Exit(reason) => return Ok(AppRunControl::Exit(reason)),
                 }
@@ -2348,6 +2353,21 @@ impl App {
                 self.stop_agents_overview_thread(app_server, thread_id)
                     .await;
             }
+            #[cfg(unix)]
+            AppEvent::StartAgentsDaemon => {
+                self.start_agents_daemon();
+            }
+            #[cfg(unix)]
+            AppEvent::AgentsDaemonStarted { result } => match result {
+                Ok(()) => self.chat_widget.add_info_message(
+                    "Background server started. Run `codex agents` in another terminal; this session remains unchanged."
+                        .to_string(),
+                    /*hint*/ None,
+                ),
+                Err(error) => self
+                    .chat_widget
+                    .add_error_message(format!("Failed to start the background server: {error}")),
+            },
             AppEvent::OpenAgentPicker => {
                 self.open_agent_picker(app_server).await;
             }