Capture rollout budget units from response usage (#36641)

## What changed

- Parse `codex_rollout_budget_units` from completed Responses API usage into
  `TokenUsage`.
- Keep the provider-only value out of serialized protocol, JSON schema, and
  TypeScript representations.

## Testing

- Cover the value in unit and end-to-end SSE response parsing tests.

GitOrigin-RevId: a53d4202beb9c8985d25894cb10e7c01f20b2a44

codex-rs/codex-api/src/sse/responses.rs

@@ -126,6 +126,8 @@ struct ResponseCompletedUsage {
     output_tokens: i64,
     output_tokens_details: Option<ResponseCompletedOutputTokensDetails>,
     total_tokens: i64,
+    #[serde(default)]
+    codex_rollout_budget_units: Option<serde_json::Number>,
 }
 
 impl From<ResponseCompletedUsage> for TokenUsage {
@@ -141,6 +143,7 @@ impl From<ResponseCompletedUsage> for TokenUsage {
                 .map(|d| d.reasoning_tokens)
                 .unwrap_or(0),
             total_tokens: val.total_tokens,
+            codex_rollout_budget_units: val.codex_rollout_budget_units,
         }
     }
 }
@@ -816,7 +819,8 @@ mod tests {
             },
             "output_tokens": 10,
             "output_tokens_details": { "reasoning_tokens": 5 },
-            "total_tokens": 110
+            "total_tokens": 110,
+            "codex_rollout_budget_units": 2.5
         }))
         .expect("valid response usage");
 
@@ -829,6 +833,7 @@ mod tests {
                 output_tokens: 10,
                 reasoning_output_tokens: 5,
                 total_tokens: 110,
+                codex_rollout_budget_units: serde_json::Number::from_f64(2.5),
             }
         );
     }

codex-rs/codex-api/tests/sse_end_to_end.rs

@@ -111,7 +111,15 @@ async fn responses_stream_parses_items_and_completed_end_to_end() -> Result<()>
 
     let completed = serde_json::json!({
         "type": "response.completed",
-        "response": { "id": "resp1" }
+        "response": {
+            "id": "resp1",
+            "usage": {
+                "input_tokens": 10,
+                "output_tokens": 5,
+                "total_tokens": 15,
+                "codex_rollout_budget_units": 2.5
+            }
+        }
     });
 
     let body = build_responses_body(vec![item1, item2, completed]);
@@ -160,7 +168,17 @@ async fn responses_stream_parses_items_and_completed_end_to_end() -> Result<()>
             end_turn,
         } => {
             assert_eq!(response_id, "resp1");
-            assert!(token_usage.is_none());
+            assert_eq!(
+                token_usage.as_ref().map(|usage| usage.total_tokens),
+                Some(15)
+            );
+            assert_eq!(
+                token_usage
+                    .as_ref()
+                    .and_then(|usage| usage.codex_rollout_budget_units.as_ref())
+                    .and_then(serde_json::Number::as_f64),
+                Some(2.5)
+            );
             assert!(end_turn.is_none());
         }
         other => panic!("unexpected third event: {other:?}"),