How can I check the status of an efm linter?

I have a linter which takes a variable amount of time to run (anywhere between 2 seconds and up to 1 minute), and I would like to have some way of distinguishing between 'linting done, no errors' and 'linting still busy'.

So I made a wrapper which I pass instead of the actual linter, that outputs 'Warning: linter started' first, then runs the actual linter, and then outputs 'Warning: linter finished' and that works once - but since the warnings are persistent and remain visible until a fresh linter execution finishes, the 'linter finished' message from the previous run remains visible, so I still can't tell if the current linter execution is finished after each edit to the file.

Note I originally posted this on vim stackexchange but someone suggested it fits better here and I agree.

Start by reviewing efm-langserver's linter execution and warning publication behavior. Determine whether the server exposes a per-run completion signal or whether the request requires a new status mechanism; done means a client can distinguish the current lint run from a previous run with no errors.