Worktree isolation checks variables set before git commands differently

Worktree isolation keeps Claude working in its own separate copy of a git repository. A guard checks git commands so they cannot reach outside that copy. A command can begin with variable assignments, such as GIT_DIR=... placed before the command name, which change how the command runs.

The guard now finds the last such assignment before the command and checks earlier assignments differently from it, with extra conditions. Before, each assignment was checked the same way.