Ensemble Message Suspense/Work Queue?

You'll need to develop the criteria yourself as it's heavily dependent upon your business logic. There's no common solution there. Generally you need to:

1. Pass some unique identifier with your request (as one of request properties or in the filename or as a header, etc.).
2. In your business service parse the response and determine  what is this response to.
3. Send deferred response

I usually have a Deferred token table where I keep track of tokens and objects to which they relate:

#Include Ensemble
/// Stored Deferred token.
/// Assumption: one BH generates only one type of Deferred token.
Class Production.DeferredToken Extends %Persistent
{

/// Token
Property token As %String;

Index IDKEY On token [ IdKey ];

/// Object's class anme
Property objectContext As %Dictionary.CacheClassname;

/// Object's primary key
Property objectId As %String;

Index objectIndex On (objectContext, objectId) [ Unique ];

/// Update ts (UTC)
Property updatedOn As %TimeStamp [ Required, SqlComputeCode = { set {*} = $$$ts}, SqlComputed, SqlComputeOnChange = (%%INSERT, %%UPDATE) ];

/// Ensemble session
Property sessionId As %Integer [ InitialExpression = {$get($$$JobSessionId)} ];

/// Ensemble BH
Property configName As %Integer [ InitialExpression = {$get($$$EnsJobLocal("ConfigName"))} ];

/// Ensemble BH class
Property ensembleContext As %Integer [ InitialExpression = {$get($$$ConfigClassName($get($$$EnsJobLocal("ConfigName")," ")))} ];

/// Tries to store a new token if possible
/// w ##class(Production.DeferredToken).add()
ClassMethod add(token As %String, class As %String = "", id As %Integer = "") As %Status
{
    return:((class'="") && ('##class(%Dictionary.ClassDefinition).%ExistsId(class))) $$$ERROR($$$ClassDoesNotExist, class)
    return:((class'="") && (id'="") && ('$classmethod(class, "%ExistsId", id))) $$$ERROR($$$GeneralError, $$$FormatText("Object '%2' from class '%1' does not exist", class, id))
    return:..IDKEYExists(token) $$$ERROR($$$GeneralError, $$$FormatText("Token '%1' already exist", token))
    
    set obj = ..%New()
    set obj.objectContext = class
    set obj.objectId = id
    set obj.token = token
    set sc = obj.%Save()
    
    return sc
}

Use %ExistsId, %DeleId, objectIndexExists, objectIndexOpen to manipulate stored tokens.