WAL and archive disks full

Hi,

What would be the best course of action for resolving a situation whereby your
postgres instance had crashed due to the wal disk and archive wal disk becoming 100% full? Say
your backups have been failing and your 'monitoring' had not reported it correctly.

You can't start the instance because it needs to write to the WAL disk (which is full), but if you
manually move WAL files off the WAL disk, the archiver will fail because it can't find WAL files it
needs to archive. The instance may also still be in backup mode, because the backups had not
completed due to the disk full situation.

Being new to postgres, im trying to understand what actions need to be taken to get the instance
back up and running without compromising recoverability...?

Thanks in advance.