Using state for heading numbering

[lunar plaza]

I would like to change the way I number headings with the use of a state variable, such that I can simply update that state to change the numbering at any point. I am using this approach for changing the supplement, which can take content however, the numbering argument requires a string and the locate function returns content even though the state has been set with a string value

#let appendix = state("appendix", false)
#let heading-numbering-fmt = state("heading-numbering-fmt", "I.A.1.")
#let heading-supplement = state("heading-supplement", "Section")

#let start-appendix() = {
  appendix.update(true)
  heading-numbering-fmt.update("A:")
  heading-supplement.update("Appendix")
}

#set heading(
  numbering: locate(loc => {heading-numbering-fmt.at(loc)}),
  supplement: locate(loc => {
    heading-supplement.at(loc)
  })
)

= Not in the appendix
<a0>
@a0

#start-appendix()

= In the appendix
<a1>
@a1

[frigid gate]

numbering has to be either a string or a function which takes the numbers and returns content

but honestly, i think you're overcomplicating this

you can just reset the heading counter

place counter(heading).update(0) in the document and the magic is done

the solution to your immediate problem, however, would be to (..numbers) => locate(...) instead of just locate

[lunar plaza]

I suppose you're right, but I would like to have it package neatly as a single function call like this, then later on I can pack other functionality or styling into it.