Chain 2 backgrounded bash commands on 1 Heroku Dyno using Procfile

Question

This Heroku Help page suggests I can run multiple commands backgrounded, followed by wait -n, in my Procfile. Their example:

web: puma -C config/puma.rb & sidekiq & wait -n

In my example, the commands I want to run are in different directories, so I wrote:

web: cd api/ && bundle exec puma -C config/puma.rb & cd .. && sh target/bin/worker & wait -n

Problem

My heroku app crashes. heroku logs shows:

2020-04-26T22:50:37.104343+00:00 app[web.1]: sh: 0: Can't open target/bin/worker
2020-04-26T22:50:55.157670+00:00 heroku[web.1]: State changed from starting to crashed

But if I do heroku run bash and then sh target/bin/worker, it runs fine. And all the files are where I expect:

$ heroku run bash
Running bash on [redacted]... up, run.[redacted] (Free)
~ $ ls -al api/config/puma.rb
-rw------- 1 u37764 dyno 1579 Apr 26 22:43 api/config/puma.rb
~ $ ls -al target/bin/worker
-rw------- 1 u37764 dyno 11952 Apr 26 22:45 target/bin/worker

So I think something may be incorrect with the way I'm chaining commands (e.g. mixing && and &). I saw this related bash question but still couldn't figure out the correct syntax.

What is it?

I also tried…

• puma needs to be run from inside the api/ directory, so e.g. web: puma -C api/config/puma.rb & sh target/bin/worker & wait -n doesn't work either.)
• web: sh start.sh where start.sh contains:

  #!/usr/bin/env sh
  cd api/
  bundle exec puma -C config/puma.rb &
  cd ..
  sh target/bin/worker &
  wait -n