anchor.diff:          pending = _inFlightRequests[request];
         }
   
  -      // Make cache request (always).
  -      _cache.get(request)
  -        .catchError(active.sendError)
  -        .then((cachedEntity) {
  -          if (cachedEntity != null) {
  -            active.submit(cachedEntity);
  -          }
  -        });
  -
         // RPC replies are handled in one place, but errors for requests are
         // subscribed to individually. This is because only in-flight requests
         // should have error returns, whereas all streams for a request care when
  
positive.code: /// The multiplexer is an intermediary that handles the routing of requests
  /// between caches and the true Apiary interface.
  class Multiplexer extends RequestHandler {
  
    /** Cache instance. */
    final Cache _cache;
  
negative.code:           return _INTERNAL_ERROR;
          })
          .then((entity) {
            if (entity != _INTERNAL_ERROR) {  
              _recordRpcData(entity);
              active.submit(entity);
            }
          })
          .whenComplete(active.close);
      }
    }
  
    Stream handle(Request originalRequest) {
      // Make a copy of the request for use in the multiplexer, since it's not
      // immutable.
      var request = originalRequest.clone();
      
      if (originalRequest.local.containsKey('noRpcAge')) {
        if (!request.isCachable) {
          throw new Exception("Cannot specify noRpcAge parameter on a non-cachable request.");
        }
        return _handleAgeQuery(request, originalRequest.local['noRpcAge']);
      }
      
      var active = _newActiveStream(request);
  
      // Only cachable requests need to be handled by the multiplexer (right now).
      if (request.isCachable) {
  
        // Make cache request (always).
        _cache.get(request)
          .catchError(active.sendError)
          .then((cachedEntity) {
            if (cachedEntity != null) {
              active.submit(cachedEntity);
            }
          });
      }
      
      _sendRpc(request, active);
      
      return active.stream;
    }
  
  