client interface:
@GET
@Path("basic")
ClientResponse<byte[]> getBasicBytes();

stacktrace:
org.jboss.resteasy.client.ClientResponseFailure: Unable to find a
MessageBodyReader of content-type text/plain for response of public
abstract org.jboss.resteasy.client.ClientResponse
org.jboss.resteasy.test.finegrain.client.ClientResponseTest$Client.getBasicBytes()
at org.jboss.resteasy.client.core.ClientInvoker.extractClientResponse(ClientInvoker.java:334)
at org.jboss.resteasy.client.core.ClientInvoker.invoke(ClientInvoker.java:229)
at org.jboss.resteasy.client.core.ClientProxy.invoke(ClientProxy.java:22)
at $Proxy19.getBasicBytes(Unknown Source)
at org.jboss.resteasy.test.finegrain.client.ClientResponseTest.testClientResponse(ClientResponseTest.java:103)

i tracked it down to this comment in Types.java
// can't figure out how to get a typed array here