Suggestions

docs/service_contract.md

@@ -75,6 +75,7 @@ option (dev.restate.ext.service_type) = SINGLETON;
 
 For keyed services, you're required to specify in every input message the field to use as key. To mark a field as key, annotate it with `dev.restate.ext.field`. Make sure that:
 
+* There is only one key field.
 * The field type is either a primitive or a message. Repeated field and maps are not supported.
 * The field type is the same for every method input message of the same service.
 

docs/service_type.md

@@ -16,7 +16,7 @@ To define the service type and key, check the [service contract](./service_contr
 
 ## Keyed service
 
-Keyed services allow to shard state and workload by a user-defined key. Each key will have its own invocations queue and its own subset of the service state. There is at most one invocation per key, but there can be multiple invocations to the same service with different keys executing concurrently.
+Keyed services allow to shard state and workload by a user-defined key. Each key will have its own invocations queue and its own state. There is at most one invocation per key, but there can be multiple invocations to the same service with different keys executing concurrently.
 
 You can think of a keyed service as a class, and of a service instance as an object instance of that class. The key is the field that **uniquely** identifies that instance, and state entries are the other fields of that class.