The %BuildIndices() supports partial rebuilding - see parameters pStartID, pEndID
In addition, you can activate/deactivate the index: Building Indices on a READ and WRITE Active System

See Data Display Options

Try this:

ClassMethod OnStartRequest() As %Status
{
  #dim %response As %CSP.Response
  
  ;s %response.ContentType="text/html",%response.Expires=-1
  s %response.Status=##class(%CSP.REST).#HTTP403FORBIDDEN
  q $$$OK
}

Or this:

/// 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 ]
{
  s %response.Status="403 Forbidden"
  q 0
}

I can't write you a direct message.

We need to look at your full code, since there is nothing suspicious in the specified piece of code. I made a small example and there is no highlighting of the last line:

Class dс.test Extends %ZEN.Component.page
{

XData Contents [ XMLNamespace = "http://www.intersystems.com/zen" ]
{
<page xmlns="http://www.intersystems.com/zen">
  <tablePane
      width="1200px"
      id="ItemsTable" 
      OnCreateResultSet="GetLog"
      maxRows="20000" 
      pageSize="20" 
      showRowNumbers="false"
      showRowSelector="false"
      showZebra="false"
      valueColumn="ID" 
      nowrap="false"
      showValueInTooltip="true"
      showFilters="true"
      autoExecute="true"
      initialExecute="false"
      useSnapshot="true" 
      onselectrow="">
  <parameter />
  <parameter />
  <parameter />
  <parameter />
  <parameter />
  <parameter />
  <parameter />
      <column colName="Sit" header="Sit name" width="50%" style="text-align:left;" filterType="text" filterOp="[" />
      <column colName="Label"  header="Label" width="10%" filterType="text" filterOp="["/>
      <column colName="userno" header="Packed By" width="10%" filterType="text" filterOp="["/>
      <column colName="LogedDate" header="Packed Date" width="10%" />
      <column colName="LogedTime" header="Packed Time" width="10%" />
      <column colName="TimeSpent" header="Spent Time" width="10%" style="text-align:left;"/>
    
  </tablePane>
  <tableNavigatorBar tablePaneId="ItemsTable"/>
</page>
}

Method GetLog(
  ByRef pSC,
  ByRef tParams)
{
  s sql = 5
  s sql(1)="SELECT 0 ID,'Sit' Sit,'Label' Label,'userno' userno,current_date LogedDate,current_date LogedTime,null TimeSpent"
  s sql(2)="union"
  s sql(3)="SELECT 1,'Sit','Label','userno',current_date,current_date,null"
  s sql(4)="union"
  s sql(5)="SELECT 2,'Sit','Label','userno',current_date,current_date,null"

  s st=##class(%SQL.Statement).%New()
  s st.%SelectMode=2
  q ##class(%SQL.Statement).%ExecDirect(st,.sql)
}

}

I confirm (used the following code):

#include %systemInclude
n
try{

  s sql="select * from (select 0 field union select 1) where 0=1"
  
  #dim rs As %SQL.StatementResult=##class(%SQL.Statement).%ExecDirect(,sql)
  w rs.%SQLCODE
  
  s st = ##class(%SQL.Statement).%New()
  $$$ThrowOnError(st.%Prepare(sql))
  s rs = st.%Execute()
  w !,"---",!,rs.%SQLCODE
  
  &sql(select * from (select 0 field union select 1) where 0=1)
  w !,"---",!,SQLCODE

}catch(ex){
  w "Error ", ex.DisplayString(),!
}

Output:
0
---
0
---
100

Quote from the documentation:

When retrieving results, first check for successful execution by examining %SQLCODE. For many statement types, success/failure is all that is needed. The %SQLCODE property contains the SQL error code value. Successful completion values are 0 (successful completion) and 100 (the operation has either found no data or reached the end of the data).^proof

My choice of a comparison tool was determined by the OS on which Studio is running. But you are free to choose something more platform-independent, such as Java or Qt.

By the way, SQL Data Lens (written in Java) already has the ability to view and upload sources to a file. It would be nice to add integration with a third-party tool for comparing items (by analogy with Studio).

I hope @Andreas Schneider will read this wish.

Can we find out what you need it for?

See Collation

Example:

s sub1=##class(%Collation).SqlString(111),
 sub2=$system.Util.Collation(444,8)
     
k t
s t(sub1,sub2)=""
s t(sub2,sub1)=""
zw t

Output:

t(" 111"," 444")=""
t(" 444"," 111")=""

This Compare only works when working with the studio, correct?

Yes, Studio does the following:

1. uploads the first source code to a temporary directory (for example c:\windows\temp)
2. uploads the second source code to a temporary directory
3. starts WinMerge by passing in the command line links to previously uploaded files: WinMerge Command line

You can do all this yourself from a batch file.
In this case, you can compare items not only in different databases, but also on different servers.

Most of the above is true for WinMerge, with one exception - WinMerge is free.
WinMerge has plugins for comparing images, PDF, Word, Visio, Excel, PowerPoint, etc.

A good question, to which I do not know a beautiful answer.
The option with Extended References, unfortunately did not work.

In general, through uploading to a file.
If the elements have different names in the databases, then you can use the Mapping a Routine/Package.

See Studio Compare

With an external program WinMerge also works fine. You can compare any elements (mac, cls, css, js, css, etc.) located both inside the database and in external files.

See Median in SQL

size = 31

ClassMethod Validate(s As %String) As %Boolean
{
 q $MATCH(s,"[1-3].*[A-CRS]")
}

size = 30

ClassMethod Validate(s As %String) As %Boolean
{
 q "ABCRS"[$e(s,*)*123[$e(s)
}