How do you set expectations in your work?

It always helps to get way ahead of potential misalignment, and then not assume that people will remember what they agreed on. Reinforce what has been discussed in a friendly way as often as possible.

In terms of work to be done: if using the agile concept properly you will have epics and features for the big picture and stories and tasks for the detailed outline of work items. No relevant information should be missing from there, it is fine to link to outside systems like a wiki and it is fine that the exact path to achieve the goals becomes more clear over time and evolves. Also on epic and feature level you will have stakeholders on the management level, so if the scope of an epic or feature would need to change, because a task is not resolvable or unexpectedly adds unplanned features (which mostly should be cool), then of course that needs to be discussed asap.

In terms of contract agreements: always have everything in writing! If that is not possible then have at least one or better more witnesses you can rely on.

Get it down on paper or in an email. Also talk about it during a meeting or a call so everybody is aware of the tasks at hand and they can keep their expectations realistic.