I'd like to have a 6th option in the Embassy.

1. It would be an interdiction for envoys to stay in the territory.
2. It would easier expell the envoys or take 3 tuns to work, giving time for the envoy.
3. It would cancel all embassy treaties or put them on hold.
4. It would create a grievance.
5. Envoys would then be treated as any infiltration unit caught on the territory, except they'll be plain visible.

It's supposed to represent the decision to severe the diplomatic relation between two empire.