Detail ADR0003

docs/adr/0003-asynchronous-duplex-api.md

@@ -8,13 +8,25 @@ Accepted
 
 ## Context
 
-The [_reactive_ nature of the Hydra node](0001-record-architecture-decisions) means _Request-response_ paradigm is not a good fit to provide a _Client API_: Clients input a _stream_ of _commands_ to a node which in turns issues a stream of _responses_ representing the observable outcome of previous commands and interaction with peers in the network.
+The [_reactive_ nature of the Hydra node](0002-reactive-core.md) means that
+clients produce a _stream_ of _inputs_ to a node which in turns issues a stream
+of _outputs_ representing the outcome of previous inputs or resulting from
+interaction with peers in the network.
+
+For example, a client may send a _command_ as _input_, upon which the node might
+do something. When that something is finished, a _output_ does indicate that.
+However, there might also be an _output_ emitted to the client when another peer
+interacted with "our" node.
+
+Queries, messages by clients which do only fetch information from the node, are
+not in scope of this ADR.
 
 ## Decision
 
-* The main API is exposed using the [Websocket](https://datatracker.ietf.org/doc/html/rfc6455) protocol with inputs and outputs conforming to some textual representation of `Command`s and `Result`s.
+* We use a single, full-duplex communication channel per client connected to a Hydra node
+* This is implemented using a simple [Websocket](https://datatracker.ietf.org/doc/html/rfc6455) with messages corresponding to `Input`s and `Output`s.
 
 ## Consequences
 
-* Client software should be implemented accordingly and most notably cannot rely on any kind of synchronous response to give feedback to potential users or higher-level clients.
-* Clients can receive "responses" decorrelated from any requests, for example as the consequence of actions carried out by other nodes
+* Clients needing a synchronous API need to implement it on top
+* Clients can receive _outputs_ decorrelated from any _inputs_ and at any time