Function compile_trigger_handler 

pub fn compile_trigger_handler(
    handler: &str,
    type_name: &str,
    on_mask: u8,
    schema: &SchemaDescriptor,
) -> Result<String, PyQLError>

Compile a schema Trigger’s handler PyQL statement (e.g. insert Note { note := __new__.name }) to a full SQL statement, for embedding in the generated plpgsql trigger function body — see ir::compile_trigger_handler for the __new__/__old__ row-context binding rules. on_mask is Pylon’s On bitmask (1=Insert, 2=Update, 4=Delete), matching TriggerDescriptor::on. Query parameters ($name) are rejected, same rule as compile_fill_expr — a trigger handler has no caller to supply them.