Config saves stop overwriting an existing file, and logout says when it could not save

What

Claude Code keeps your settings, and some sign-in details, in a config file. Two changes make saving that file safer. Both are linked to a new environment variable (a named setting you can set before starting a program), CLAUDE_CODE_ENABLE_CONFIG_MISSING_READ_GUARD, which did not exist before.

• When saving the global config file through its fallback path, Claude Code can now create the file only if it does not exist yet (createOnly). If a file has appeared there in the meantime, the write is refused and the save is retried on top of the existing file, up to a limit. Before, this fallback always overwrote the file, so a moment when the file could not be read could wipe a real config.
• The project config helpers return early when the file is missing and the environment variable is set.
• A change that only touches a cached key no longer counts as significant enough to save.
• Logout now reports a failure when it cannot save the config file. /logout shows an error saying your account or API key may still be in the config file and to run claude auth logout again. claude auth logout prints 'Logout failed: …'. Before, logout always reported success.
• Logout also prunes or deletes additional stores where credentials are kept, and with the environment variable set it also clears primaryApiKey.

Why

A config file that is briefly unreadable should no longer be replaced with an empty one, which could lose your sign-in and settings. And if logout cannot finish, you are told so, instead of believing you are signed out while your key is still on disk.