Wait, spoke too soon.
<p>
Now it runs under undroidwish/vanillawish, but does NOT find it under the native wish 8.6, BLT 2.5.3.  (it did work under native wish 8.5, BLT 2.4z)
<p>
The error message now is 
<pre>
   cant't read "::blt::zoomInfo(...,stack)": no such variable
</pre>

And, of course, taking out ::blt:: restores it to full function.