I am trying to create essentially a common cache across multiple branches regardless of lockfile sum. In the documentation it is specified that the 'shared-key' field is:

A cache key that is used instead of the automatic job-based key

however when I specify a 'shared-key' the lock files and other parameters are still used in the cache key which results in many copies of the cache (which is quite large). I am wondering:

a) is it possible to fully specify the cache key
b) what is the preferred method for reusing a single cache across multiple branches with modifications.

I understand that this will probably slow down build times slightly because the incremental build will not be a perfect fit however it is preferable than rebuilding from scratch (and creating a ~2gb cache) each time a new branch is pushed