what's best way to manager many items priority

There are many observers for a event.

Observers need to process event in specific order.

Observers belong to different modules. they are all plugin/mods.

how can i manager the order in an elegant way.

Way 1:

declare the priority in a config file. maybe:

  observers = {
  
    "modA",
    "modB",
  }

but this is not plugable. i have to declare all before application startup.

Way 2: every observer define a interface:

//file a
function modA:getPriority()
    return 99
end

//file b
function modB:getPriority()
    return 98
end

now priority is decided on running time. And different observer live in different source file .

but i can not figure out who has lower priority than modA easily. i need to search all source directory.

if i have a new mod that need in middle of modA and modB, i have to write 98.5...

so, is there someway better than my ways.