A new safety mechanism prevents concurrent config writes from wiping authentication data in ~/.claude.json. Before writing, the system re-reads the file and refuses to proceed if the disk version is missing oauthAccount or hasCompletedOnboarding data that exists in the in-memory cache. This addresses a race condition reported in GitHub issue #3117.
Evidence
Config lock function (search for "saveConfigWithLock", "re-read config is missing auth that cache has")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.