Report selected environment connection transitions (#33251)

## What changed

- Track connected and disconnected states across initial remote exec-server connections and reconnection attempts.
- Emit experimental `thread/environment/connected` and `thread/environment/disconnected` app-server notifications for each thread selecting the environment. Each payload identifies the thread and environment; current state is not replayed when a thread starts.
- Stop forwarding connection events when an environment selection is removed or replaced.

## Testing

- Cover connection, disconnection, reconnection, shared-environment notifications, and replacement of a selected environment.

GitOrigin-RevId: 5dd767372363c4a2a8319fc16164be117d5bd20c

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

@@ -169,6 +169,8 @@ pub(super) fn server_notification_thread_target(
         | ServerNotification::AccountUpdated(_)
         | ServerNotification::AccountRateLimitsUpdated(_)
         | ServerNotification::AppListUpdated(_)
+        | ServerNotification::EnvironmentConnected(_)
+        | ServerNotification::EnvironmentDisconnected(_)
         | ServerNotification::RemoteControlStatusChanged(_)
         | ServerNotification::ExternalAgentConfigImportProgress(_)
         | ServerNotification::ExternalAgentConfigImportCompleted(_)

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

@@ -208,6 +208,8 @@ impl ChatWidget {
             | ServerNotification::McpToolCallProgress(_)
             | ServerNotification::McpServerOauthLoginCompleted(_)
             | ServerNotification::AppListUpdated(_)
+            | ServerNotification::EnvironmentConnected(_)
+            | ServerNotification::EnvironmentDisconnected(_)
             | ServerNotification::RemoteControlStatusChanged(_)
             | ServerNotification::ExternalAgentConfigImportProgress(_)
             | ServerNotification::ExternalAgentConfigImportCompleted(_)