Macro upsert_source_time_unit 

macro_rules! upsert_source_time_unit {
    ($($ty:ty),+ $(,)?) => { ... };
}

Source times whose sources never render the upsert envelope (MySQL and SQL Server CDC). Order = () keeps the generic render path free of any columnar requirement on the source time. The projection panics rather than returning: () would collapse every from_time to equal, silently breaking “latest offset wins” dedup, so if such a source ever reaches the upsert path we want a loud failure, not arbitrary per-key output.