Function delete_records_trim_decision 

pub const fn delete_records_trim_decision(
    facts: DeleteRecordsTrimFacts,
) -> DeleteRecordsTrimDecision

Admit a trim and cap it at every logical deletion frontier.

-1 means the current high watermark, which is always admitted. An explicit request above the high watermark is refused RejectOutOfRange, matching UnifiedLog.maybeIncrementLogStartOffset on Kafka trunk: an explicit offset never enters the uncommitted tail, even when it is still below the log end offset. A scheduled topic adds its delivery watermark as a second cap on top of the high watermark. Stale and repeated requests return the current start and never move it backwards.