Complete the frustrated host's realization.

I ______ all afternoon making this elaborate five-course meal! My guests just texted me to say they stopped for pizza on the way here and are completely full.

The correct answer is needn't have cooked.

We use needn't have + past participle when an action was actually performed, but we later realize it was unnecessary and a waste of time or effort. The host did cook the meal, but the guests were already full.

We use didn't need to + infinitive when an action was unnecessary, and because of that, it usually wasn't performed.