Function log_time_index_widening_overflow 

fn log_time_index_widening_overflow(
    region_id: RegionId,
    version: &Arc<Version>,
    request: &RegionAlterRequest,
)

Logs a time index unit widening whose rescaled values would overflow the target unit’s i64 range in existing data. Memtables are flushed before an alter, so each SST’s time range bounds its values; overflowing values cast to NULL on read, which is deemed acceptable.