Stale response
A cached answer older than its fresh window, served now while it refreshes.
What it means
Serving a slightly old answer immediately, and refreshing it in the background, keeps latency low. The trade-off is that the caller must be told the data is not brand new.
How Onekey handles it
metadata.stale: true means the copy is past its fresh window. You still get it instantly and free, and Onekey refreshes it in the background. If a refresh fails and a recent-enough copy exists, you get that copy with stale: true instead of an error. Read age_s if freshness matters.