The PR #2438 added support for systemd services of type notify.

# lib/puma/systemd.rb
module Puma
  class Systemd
    ...
    
    def hook_events
      @events.on_booted { SdNotify.ready }
      @events.on_stopped { SdNotify.stopping }
      @events.on_restart { SdNotify.reloading }
    end
    
    ...
  end
end

The Problem:
The systemd status gets updated as expected when performing a hot restart.
But the status stays active when performing a phased restart.
In the current implementation, SdNotify.reloading is never called during a phased restart.

A Common Scenario:
If we perform a phased restart, Puma terminates an old worker and starts a new one.
And if Puma is not able to boot up a new worker for some reason, it keeps trying.

In this case, the systemd status shouldn't stay active.
During a phased restart the status should be reloading.

Additional Context:
We monitor the status of all our systemd processes.
If the status of a process is not active any more (for a certain period of time), we get notified.

It would be awesome to keep this monitoring approach for Puma as well.