Function timestamp_available 

pub const fn timestamp_available() -> bool

Whether [__timestamp_ns] can answer with a real clock.

false means every Record::timestamp_ns is 0 and anything DERIVED from the timestamp — the throttle windows above all of them — has no time base: a throttled site then emits its FIRST record and nothing after it (a clock that never moves is a window that never elapses — issue 1152). Exposed so a wrapper can say so out loud instead of degrading quietly: without this, a throttled C call site looks identical whether it is rate-limiting or permanently shut.