Context state whose fields exist only under this crate’s cfg: the commit
lock that tests hold and the local send clock (always present on wasm32).
Another crate builds it with Default, so its own features need not match
this crate’s.
The context core code runs on: storage, the API client, the identity,
events and the client’s plain settings. Features is what the crates above
core add; each of them reads its own part through its own trait.