Background information here: https://en.wikipedia.org/wiki/United_Kingdom%E2%80%93United_States_free_trade_agreement
Market resolves according to the date the agreement is effective, not the date it is signed. I'm expecting that if the agreement ever gets signed, the above page will look a bit more like this one: https://en.wikipedia.org/wiki/Australia%E2%80%93United_Kingdom_Free_Trade_Agreement, in which case I will take the date next to the "effective" field.
If the UK and the US enter into a multilateral FTA that includes other countries, that triggers resolution. If the UK and US enter into a trade agreement that falls short of an FTA, that does not trigger resolution.
Free trade agreements have a pretty universal definition so I don't anticipate any complications in resolution. I will bet in this market.
Feel free to add later years and/or bet on the "other" option. Only answers of the form of a single year will be accepted.
Close date extends as necessary.