Function check_partial_record_fits 

fn check_partial_record_fits(
    records_read: usize,
    remaining_records: usize,
) -> Result<()>

Checks that a partial record can still be flushed into the caller’s record budget.

Reaching the end of a page with a record delimiter means the decoder stopped because it ran out of levels, not records, so it cannot have used up the whole budget. A page whose repetition levels disagree with its record count breaks that, and flushing the partial record would then take the count past what was asked for.