https://github.com/apache/airflow/pull/12139 added some new params to the scheduler -- we have "cursory" docs for them in the comments in the config file, but we should have a more details docs in the scheduler.rst page.
airflow/jobs/scheduler_job.py
dag = dagbag.dags[request.dag_id]
        dag_run = dag.get_dagrun(execution_date=request.execution_date, session=session)
        dag.handle_callback(
            dagrun=dag_run, success=not request.is_failure_callback, reason=request.msg, session=session
        )
    def _execute_task_callbacks(self, dagbag: DagBag, request: TaskCallbackRequest):
        simple_ti = request.simple_task_instance
        if simple_ti.dag_id in dagbag.dags:
            dag = dagbag.dags[simple_ti.dag_id]
            if simple_ti.task_id in dag.task_ids:
                task = dag.get_task(simple_ti.task_id)
                ti = TI(task, simple_ti.execution_date)
                
                ti.start_date = simple_ti.start_date
                ti.end_date = simple_ti.end_date
                ti.try_number = simple_ti.try_number
                ti.state = simple_ti.state
                ti.test_mode = self.UNIT_TEST_MODE
                if request.is_failure_callback:
                    ti.handle_failure(request.msg, ti.test_mode, ti.get_template_context())
                    self.log.info('Executed failure callback for %s in state %s', ti, ti.state)
    @provide_session
    def process_file(