Function merge_usage_counters

src/sessions/codex.rs:935–945

Add `add`'s numeric counters field-wise into `existing` (both are usage objects). Used when several flushes land on the same assistant message (e.g. an aborted turn with no reply of its own).

(existing: &mut Value, add: &Value)

/// objects). Used when several flushes land on the same assistant message
/// (e.g. an aborted turn with no reply of its own).
pub(crate) fn merge_usage_counters(existing: &mut Value, add: &Value) {
    let (Some(map), Some(add_map)) = (existing.as_object_mut(), add.as_object()) else {
        return;
    };
    for (key, value) in add_map {
        if let Some(count) = value.as_i64() {
            let current = map.get(key).and_then(Value::as_i64).unwrap_or(0);
            map.insert(key.clone(), Value::from(current.saturating_add(count)));
        }
    }
}

/// Attach the finished turn's summed usage to the most recent assistant
/// message of the batch (the reply the turn's `token_count` events report