Following up in case someone else runs into this problem. I changed the function the CHECK statement called to raise a warning. Not perfect, but noticeably better. I don't get the column that failed but I do get what bad input gummed things up.
CREATE OR REPLACE FUNCTION po.confirm(p_val anyelement, p_validated boolean) RETURNS boolean LANGUAGE plpgsql STRICT IMMUTABLE PARALLEL SAFE AS $$ BEGIN IF NOT p_validated THEN RAISE WARNING 'Invalid value: %', p_val; END IF; RETURN p_validated; END; $$; COMMENT ON FUNCTION po.confirm(anyelement,boolean) IS 'Raises a warning when a condition is false; useful for outputting CHECK constraint error values.';
CREATE DOMAIN po.email AS varchar
CHECK (po.confirm(VALUE, VALUE IS NULL OR NOT po.email_expanded(VALUE) IS NULL));
The blunt force answer is to not use bulk inserts. Try COPY; it's good at saying which record throws an error.
Sadly, this is a cloud-managed database without direct access to 5432 from outside the VPC and bastian instances are frowned upon by our security folks. Guess I'm stuck with bisecting. Thanks for the confirmation.
