Is the answer "downstream projects" ?

if you please give more practical example, how this could be used ... ?

If you have a github org with 100 projects that compiles with ./configure && make && make install
You have to create 100 directories with same files ?

I want one project to scan them all or one project to apply to a list of names (here repo names).

probably not exactly what we're talking about but this where FTP protocol could be useful.

You can spin up an supplemental application which accepts requests (say through a web hook) and dispatch all of them to the same Sparky build bypassing repo specific parameters.

For example:

.sparky/projects/make/sparky.yml

allow_manual_run: false # this project only built though an supplemental web app, using sparky  FTP proto
sparrowdo:
  docker: debian 
  no_sudo: true  

.sparky/projects/make/sparrowfile

say conf()<repo>;
say conf()<commit>;
# do something with repo and commit, you got the idea

Application's cro http route:

post -> 'queue', :%params {
 
  my $sparky-dir = "{%*ENV<HOME>}./sparky/projects/make";

  my $rnd = ('a' .. 'z').pick(20).join('');

  my $id = "{$rnd}{$*PID}";

  request-body -> (:$repo, :$commit ) {

     # this directory is used as to keep build unique configuration  
     my $build-dir = "/some/local/dir/${$id}"; 
     
    # write up build configuration
    spurt "{$build-dir}/config.pl6", %(
        repo => $repo,
        commit => $commit
     ).perl;

    # write up a trigger data with sparrowdo configuration and build CWD
    spurt "{$sparky-dir}/.triggers/$id", %(
       sparrowdo => %( 
           conf => "{$build-dir}/config.pl6", 
         ),
         description => "build for {$repo and $commit}",
        ).perl
    );
  }
}

You could also see how this is implemented in RakuPlay - https://github.com/melezhik/RakuPlay/blob/main/lib/RakuPlay.rakumod#L40-L61.

Of course this supplemental application should have a write access to Sparky file system, because it's File Triggering Protocol 😄