The shared in-memory key-value store, a single GenServer backing every endpoint.

It holds two independent keyspaces so both the bucketed and bucketless protocols can share one process:

• a bucketed space — put/3,4, get/2, delete/2 take (bucket, key) (and keys/1 takes just (bucket)) and are used by FakeRiak.Riak;
• a bucketless space — put/2, get/1, delete/1 take just (key) and are used by FakeRiak.Redis, FakeRiak.Etcd and FakeRiak.Memcached.

The bucketed space models Riak's siblings: each key holds a list of values, so get/2 replies {:ok, values} with a non-empty list. put/4 takes a merge mode — :append adds the value as a new sibling (byte-identical values are deduplicated, as real Riak does), while :replace collapses the key to a single value, the way resolving with a vector clock does. put/3 defaults to :replace. The bucketless space stays strictly last-write-wins: its get/1 replies {:ok, value} with a single value.

In both spaces get replies {:error, reason} when absent, and put/delete reply :ok (with delete returning {:error, reason} when the key is absent). The public functions run in the caller's connection process, so when --verbose is set they log each operation, attributed to that connection's protocol.