[mkehrt]

IANAL, but this is my understanding.

What's the consideration in the written offer? Promises aren't enforceable in court. For a contract to be enforceable, it has to be an exchange of something, not a one sided offer.

https://www.law.cornell.edu/wex/consideration

[tzs]

There are substitutes for consideration. Search for "detrimental reliance" and "promissory estoppel" if you want to go down that rabbit hole.