previousMappingsFile

File where the previous run's mappings JSON lives, used for the boot-time pre-deploy step. Returns the file even if it doesn't exist yet — callers check exists() themselves.

Boot-time pre-deploy is needed because Geyser's GeyserDefineCustomItemsEvent is a once-per-boot lifecycle event, so the custom-item set comes from whatever's in custom_mappings/ at Geyser's startup. RPM's conversion finishes AFTER that point, so the just-generated mappings can only take effect next boot — which we accomplish by writing them to output/ on this boot and copying them to Geyser on the next boot.