The response can include public operational freshness metadata when available.
Event-level provenance remains on each event through scheduleSourceKind,
scheduleSourceUrl, and scheduleNote.
Heuristic events are estimated windows and are not treated as source-native
pre-release alert triggers.
The API clamps access to the caller's signed-in entitlement. Visitors receive
the gradient preview even if they request a higher window; Research and Pro can
request their unlocked calendar windows.