Configure Airflow 3 TaskFlow API tasks with explicit typed XCom serialization to avoid implicit pickling of large objects

Steps

1. Decorate task functions with @task and return only JSON-serializable primitives or dataclasses; avoid returning DataFrames or large objects directly
2. Enable custom XCom backends by setting xcom_backend in airflow.cfg to a class implementing BaseXCom.serialize_value and deserialize_value to store large artifacts in external storage (e.g., S3) and only put the URI into the XCom table
3. Pass XCom values between tasks using the TaskFlow return value syntax: downstream_task(upstream_task()) so Airflow generates the XCom dependency automatically
4. Use multiple_outputs=True on a @task decorator when the function returns a dict and you want each key to be an individually addressable XCom key
5. Set [core] max_active_runs_per_dag and enable_xcom_pickling=False in airflow.cfg (the default in Airflow 3) to enforce JSON-only serialization and surface serialization errors early