Show estimated thread usage in /status (#38281)

## What changed

- Extend `account/usage/read` with an optional `threadId` request and a
  backward-compatible `threadUsage` response containing estimated credits,
  optional USD cost, and model, reasoning, speed, and token breakdowns.
- Fetch thread usage for eligible Business and Enterprise plans when `/status`
  is opened, then update the rendered status card asynchronously.
- Preserve terminal scrollback when replacing a visible status-card tail, and
  append a refreshed card when the original tail can no longer be updated.

## Testing

- Add app-server coverage for authentication, canonical thread IDs,
  unavailable billing routes, and malformed IDs.
- Add TUI coverage for usage formatting, stale responses, retries, history
  updates, terminal reflow, and scrollback preservation.

GitOrigin-RevId: 49300914b3fba917c0f08e8595363e04e5ba6d37

codex-rs/tui/src/app_event.rs

@@ -47,6 +47,7 @@ use crate::app_server_session::AppServerStartedThread;
 use crate::bottom_pane::ApprovalRequest;
 use crate::bottom_pane::StatusLineItem;
 use crate::bottom_pane::TerminalTitleItem;
+use crate::chatwidget::ThreadUsageOutcome;
 use crate::chatwidget::UserMessage;
 use crate::goal_files::GoalDraft;
 use codex_app_server_protocol::AskForApproval;
@@ -452,6 +453,19 @@ pub(crate) enum AppEvent {
         result: Result<GetAccountTokenUsageResponse, String>,
     },
 
+    /// Fetch backend-estimated usage for the currently visible enterprise thread.
+    RefreshThreadUsage {
+        thread_id: ThreadId,
+        request_id: u64,
+    },
+
+    /// Result of fetching backend-estimated usage for a specific thread.
+    ThreadUsageLoaded {
+        thread_id: ThreadId,
+        request_id: u64,
+        result: Result<ThreadUsageOutcome, String>,
+    },
+
     /// Fetch workspace messages for the status-line headline item.
     RefreshStatusLineWorkspaceHeadline {
         request_id: u64,