You wrong because you missed something important in the documentation. The third parameter is not about string, it is about the list of chars, and the last one the same. So, it will remove everything at the beginning if any of defined characters it will be. And order does not matter.

Write $ZSTRIP("ZZZZTESTSLOCKTEST","<","ETSZ")

return the same

If you have to remove fixed string, you can use $piece or $replace

Write $p("ZZZZTESTSLOCKTEST","ZZZZTEST",2,*)
SLOCKTEST

Each Application Server uses own Global Buffer plus Server Buffer, to fetch data, but the speed of the connection between those servers also matter.

If you don't care where to run so rare queries, you can do it on Database Server. ECP connection only gives a way to get access to the data in databases. And does not help to call any code on Database Server directly. And since %Net.RemoteConnection already deprecated, you can use other ways to call the main server or any other, and SOAP can be one of the ways, but I would prefer JSON Rest API, which in result will transfer fewer data.

To set any response header, you should overwrite OnPreHTTP method in your CSP Page class.

 Class User.Page Extends %CSP.Page
{

ClassMethod OnPage() As %Status
{
  &html<<html>
<head>
</head>
<body>>
  ; To do...
  &html<</body>
</html>>
  Quit $$$OK
}

/// Event handler for <b>PreHTTP</b> event: this is invoked before
/// the HTTP headers for a CSP page have been sent. All changes to the
/// <class>%CSP.Response</class> class, such as adding cookies, HTTP headers,
/// setting the content type etc. must be made from within the OnPreHTTP() method.
/// Also changes to the state of the CSP application such as changing
/// %session.EndSession or %session.AppTimeout must be made within the OnPreHTTP() method.
/// It is prefered that changes to %session.Preserve are also made in the OnPreHTTP() method
/// as this is more efficient, although it is supported in any section of the page.
/// Return <b>0</b> to prevent <method>OnPage</method> from being called.
ClassMethod OnPreHTTP() As %Boolean [ ServerOnly = 1 ]
{
  Do %response.SetHeader("X-MyHeader", "some info")
  quit 1
}

}

In the first implementation, I tried to actually build the tree. But missed something, and got some duplications in the lowest branches. Then using the same tree trying to solve second part, I found more than one unbalanced branches and a long time had not noticed how it could be until I noticed duplications. Then I removed this way, and first part becomes much simpler if just search node which does not have parents. In the second part, you actually already have a tree when you know when it started from the first part.

Looks like just some simple implementation for Long Pulling requests.

But how about getting not just a progress but how to get some data before task finished. 

And also, I see beg security Issue, when I can get information from any other process. You use TaskId directly from the request like you trust everybody. And also easy to get SUBSCRIPT error.

BTW: do you suppose to acept someone's answer? Looks like it is mostly just discissing topic.

For current process

USER>f fmt="enuw","rusw","current","" do ##class(%SYS.NLS.Format).%New(fmt) w !,fmt,?10,$zd($h,11),?15,$zd($h,12)
 
enuw      Wed  Wednesday
rusw      Сре  Среда
current   St   středa
          Wed  Wednesday

Or for all new processes, without restart

%SYS>write $zd($h,12)
Wednesday
%SYS>Set ^SYS("NLS","Config","LocaleFormat")=1
 
%SYS>write $zd($h,12)
Wednesday
%SYS>Do Locale^NLSLOAD("rusw")
 
%SYS>write $zd($h,12)
Среда