Patterns from a few.

One example can be a fluke. The agent copies a quirk you did not mean. A small set shows what repeats.

Give two or three short samples. Name the pattern you want repeated. Ask for a new piece that fits the set.

These subject lines are the pattern: short, no pun, a concrete noun.
— Pallet still missing
— Friday class of 18
— New date from Mara
Write three more subject lines in the same pattern for an email about a delayed printer.

Read the three new lines. If one jokes or goes long, the pattern was not held.

A tiny set you can grow. Three good samples are a style guide.