Show token used when context window is unknown (#7497)

- Show context window usage in tokens instead of percentage when the
window length is unknown.

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

@@ -297,6 +297,41 @@ fn token_count_none_resets_context_indicator() {
     assert_eq!(chat.bottom_pane.context_window_percent(), None);
 }
 
+#[test]
+fn context_indicator_shows_used_tokens_when_window_unknown() {
+    let (mut chat, _rx, _ops) = make_chatwidget_manual();
+
+    chat.config.model_context_window = None;
+    let auto_compact_limit = 200_000;
+    chat.config.model_auto_compact_token_limit = Some(auto_compact_limit);
+
+    // No model window, so the indicator should fall back to showing tokens used.
+    let total_tokens = 106_000;
+    let token_usage = TokenUsage {
+        total_tokens,
+        ..TokenUsage::default()
+    };
+    let token_info = TokenUsageInfo {
+        total_token_usage: token_usage.clone(),
+        last_token_usage: token_usage,
+        model_context_window: None,
+    };
+
+    chat.handle_codex_event(Event {
+        id: "token-usage".into(),
+        msg: EventMsg::TokenCount(TokenCountEvent {
+            info: Some(token_info),
+            rate_limits: None,
+        }),
+    });
+
+    assert_eq!(chat.bottom_pane.context_window_percent(), None);
+    assert_eq!(
+        chat.bottom_pane.context_window_used_tokens(),
+        Some(total_tokens)
+    );
+}
+
 #[cfg_attr(
     target_os = "macos",
     ignore = "system configuration APIs are blocked under macOS seatbelt"