How do I fix this?
I tried editing at https://toolsadmin.wikimedia.org/tools/id/abbreviso .
The only relevant field is "Path to tool below main webservice" which I guess is supposed to be the relative path to the tool's main page?
Changing it only changes the link for the title at https://toolsadmin.wikimedia.org/tools/id/abbreviso
it doesn't seem to affect the link for the title at https://admin.toolforge.org/tool/abbreviso
(whether I put empty-string, '/', 'abbreviso/' or an absolute URL).
(The nodejs tool itself is configured to allow paths with or without the /abbreviso/ part).

Ok, thanks for explaining that in detail!

Thanks! Is enwiki is miser mode? I looked at meta=siteinfo for misermode and it is neither true nor false but empty-string (which to me suggests false or default, which is also false).