[VenRoot]

What

Clear the repository-local environment exported by Git before the pre-push hook runs preflight.

Why

In linked worktrees, fixture Git commands can inherit the pushed worktree's GIT_DIR/index and read or modify the wrong repository. Save the hook root, unset the variables returned by git rev-parse --local-env-vars, then run the existing gate with unchanged marker/ref behavior.

Test plan

• Complete default preflight passes in isolation — established upstream font-test blockers remain; no full gate pass claimed.
• Fresh compatibility check against upstream 474dc8a: conflict-free merge; both changed files remain unchanged upstream.
• Hook regression 18/18 passed; marker suite 35/35 passed. The original hook failed the new linked-worktree regression.
• Previous lint, Bash syntax and whitespace checks passed. ShellCheck unavailable.

Notes for reviewer

Only tools/scripts/git-hooks/pre-push and tools/scripts/tests/test-pre-push-hook.sh change. The regression invokes a real hook and safely reads a foreign fixture's absolute Git directory. No gate bypass, pointer change, hook configuration change or dependency on another source contribution.

Upstream fd78ba1 separately fixes mutation.sh's temporary-path cleanup trap; that does not fix Git environment contamination and is not included here. Draft while existing full-gate limitations remain.