Claude Code checks git commands before running them, to protect against git writing where it should not. ARGV0 is an environment variable, a named value passed to a program when it starts, and it changes the name a program is started under.
When a git command sets ARGV0, the check now refuses it with a specific message. The message says that ARGV0 changes the name git is started under, so the git subcommand that would run cannot be verified. Before, such a command only got a general message about environment settings Claude Code could not inspect.
If git could be started under a different name, Claude Code could not be sure which git action was actually going to run. Refusing these commands closes a way around the git write protection, and the new message tells you exactly why the command was stopped.