Players were losing character data (inventory, armor, backpack) after
each launcher update because config.json corruption wiped the UUID
mapping. Same username, new UUID = server treats as new player.
Fix: UUIDs now stored in separate uuid-store.json that saveConfig()
can never touch. Added safety check to refuse destructive writes
when config file exists but loads empty. Includes 28 regression tests.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
