Expose context usage in statusline state (#61409)

## What changed

Add `thread.usage.context` with optional `context_window_size`, `used_tokens`, and `used_percentage` fields. Use the latest token report for context usage and the built-in footer's window size and percentage calculations. Omit unavailable fields, including the percentage when the context window is unknown.

## Testing

Extend statusline state tests to cover missing usage, unknown context windows, and footer-consistent percentages, with context usage distinct from cumulative token totals.

GitOrigin-RevId: 699b65f6c047e76fcc7d1ba729eebd19a19e4bcd

codex-rs/tui/src/chatwidget/statusline_state/usage.rs

@@ -6,10 +6,21 @@ use serde::Serialize;
 
 #[derive(Serialize)]
 pub(super) struct Usage {
+    context: Context,
     #[serde(skip_serializing_if = "Option::is_none")]
     total: Option<Counts>,
 }
 
+#[derive(Serialize)]
+struct Context {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    context_window_size: Option<i64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    used_tokens: Option<i64>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    used_percentage: Option<i64>,
+}
+
 #[derive(Serialize)]
 struct Counts {
     total_input_tokens: i64,
@@ -52,7 +63,17 @@ impl Counts {
 
 impl From<&ChatWidget> for Usage {
     fn from(chat: &ChatWidget) -> Self {
+        let context_window_size = chat.status_line_context_window_size();
         Self {
+            context: Context {
+                context_window_size,
+                used_tokens: chat
+                    .token_info
+                    .as_ref()
+                    .map(|info| info.last_token_usage.tokens_in_context_window()),
+                used_percentage: context_window_size
+                    .and_then(|_| chat.status_line_context_used_percent()),
+            },
             total: chat
                 .token_info
                 .as_ref()

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

@@ -388,6 +388,7 @@ async fn app_server_model_verification_renders_warning() {
 async fn context_indicator_shows_used_tokens_when_window_unknown() {
     let (mut chat, _rx, _ops) = make_chatwidget_manual(Some("unknown-model")).await;
 
+    chat.thread_id = Some(ThreadId::new());
     chat.config.model_context_window = None;
     let auto_compact_limit = 200_000;
     chat.config.model_auto_compact_token_limit = Some(auto_compact_limit);
@@ -399,18 +400,39 @@ async fn context_indicator_shows_used_tokens_when_window_unknown() {
         ..TokenUsage::default()
     };
     let token_info = TokenUsageInfo {
-        total_token_usage: token_usage.clone(),
-        last_token_usage: token_usage,
+        total_token_usage: token_usage,
+        last_token_usage: TokenUsage {
+            total_tokens: 40_000,
+            ..TokenUsage::default()
+        },
         model_context_window: None,
     };
 
-    handle_token_count(&mut chat, Some(token_info));
+    handle_token_count(&mut chat, Some(token_info.clone()));
 
     assert_eq!(chat.bottom_pane.context_window_percent(), None);
     assert_eq!(
         chat.bottom_pane.context_window_used_tokens(),
         Some(total_tokens)
     );
+    let state = serde_json::to_value(chat.statusline_state()).unwrap();
+    assert_eq!(
+        state["thread"]["usage"]["context"],
+        json!({"used_tokens": 40_000})
+    );
+
+    handle_token_count(
+        &mut chat,
+        Some(TokenUsageInfo {
+            model_context_window: Some(68_000),
+            ..token_info
+        }),
+    );
+    let state = serde_json::to_value(chat.statusline_state()).unwrap();
+    assert_eq!(
+        state["thread"]["usage"]["context"],
+        json!({"context_window_size": 68_000, "used_tokens": 40_000, "used_percentage": 50})
+    );
 }
 
 #[tokio::test]

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

@@ -34,7 +34,7 @@ async fn statusline_state_projects_the_displayed_settings() {
             "config": {"statusline_items": ["run-state"]},
             "thread": {
                 "workspace": {"cwd": expected_cwd},
-                "usage": {},
+                "usage": {"context": {}},
                 "id": id, "name": "Saved carts", "agent": {"state": "ready"},
                 "model": {"id": "gpt-5.5", "display_name": "Test model", "provider": "openai",
                     "reasoning_level": "none", "service_tier": "acme-priority", "service_tier_display_name": "Turbo"},
@@ -92,3 +92,30 @@ async fn statusline_totals_use_the_reported_token_breakdown() {
         assert_eq!(state["thread"]["usage"].get("total").is_some(), has_total);
     }
 }
+
+#[tokio::test]
+async fn statusline_context_uses_the_footer_window_and_percentage() {
+    let (mut chat, _events, _ops) = make_chatwidget_manual(Some("gpt-5.2")).await;
+    chat.handle_thread_session(configured_thread_session(ThreadId::new()));
+    chat.config.model_context_window = Some(80_000);
+    helpers::handle_token_count(&mut chat, /*info*/ None);
+    let state = serde_json::to_value(chat.statusline_state()).unwrap();
+    assert_eq!(
+        state["thread"]["usage"]["context"],
+        json!({"context_window_size": 80_000})
+    );
+
+    // The last response occupies half the usable window after the footer's fixed overhead.
+    let mut info = helpers::make_token_info(
+        /*total_tokens*/ 56_000, /*context_window*/ 100_000,
+    );
+    info.total_token_usage.total_tokens = 220_000;
+    helpers::handle_token_count(&mut chat, Some(info));
+    let state = serde_json::to_value(chat.statusline_state()).unwrap();
+    assert_eq!(
+        state["thread"]["usage"]["context"],
+        json!({
+            "context_window_size": 100_000, "used_tokens": 56_000, "used_percentage": 50
+        })
+    );
+}