Struct EventUpcaster 

pub struct EventUpcaster {
    pub event_type: &'static str,
    pub from_version: u64,
    pub to_version: u64,
    pub transform: fn(event: &EventRecord) -> Result<Vec<u8>, UpcastError>,
}

A stateless, pure transformation that converts an event payload from one version to another.

Upcasters are plain structs with function pointers — no traits, no boxing, no dynamic dispatch. They are returned as static slices (&'static [EventUpcaster]) for zero allocation overhead.

Fields

event_type: &'static str

from_version: u64

to_version: u64

transform: fn(event: &EventRecord) -> Result<Vec<u8>, UpcastError>