Function fire_before_triggers 

pub fn fire_before_triggers(
    registry: &TriggerRegistry,
    diff: TriggerDiff,
    reader: &dyn GraphReader,
    writer: &dyn GraphWriter,
    procedures: &ProcedureRegistry,
) -> Result<()>

Fire every registered before-phase trigger against the pre-commit diff. Returns Ok if every trigger ran cleanly, Err with the offending message if one failed — propagated to abort the originator’s commit. Trigger writes are buffered into the supplied writer so the caller can merge them into the prepared command batch.

Unlike after-firing, before-firing stops at the first error: the user’s commit hasn’t happened yet, so a failing before- trigger cleanly aborts everything.