yes, there is a contract. its Rousseau's social contract: Each of us places his person and authority under the supreme direction of the general will, and the group receives each individual as an indivisible part of the whole
at my startup, we didn't have any coding standards, except one: don't reformat other people's code.
this meant that the original author of the compilation unit (uh, file) had the freedom to do what he wanted, and other people who made modifications had to conform to the original format.
the results:
1. no fights over coding standards, although we did have plenty of banter
2. it taught people to respect the other people's style if they wanted their own style respected, thereby making everyone complicit and fluent in every style
except for programmers