test_git_learning mutates worktree branches during pre-push runs

[EtanHey]

Summary

tests/test_git_learning.py appears to create real commits in the active repository context when the full pre-push suite runs from a git worktree. Because worktrees share the git object database with the parent repo, those fixture commits can leak into the feature branch under test.

Evidence

• In /private/tmp/brainlayer-phaseb-b2, a pre-push run regrew stray commits after a hard reset:
  • 320fcb63 feat: add app bootstrap
  • 75c7589f fix: handle startup failure
• The same 10-test slice passed cleanly on a fresh clean clone at 464a04f7 and did not mutate HEAD.
• The commit subjects match fixture data embedded in tests/test_git_learning.py.

Why this matters

• Worktree-based publication flows can end up with test-fixture commits silently attached to the branch being pushed.
• This makes pre-push results environment-dependent and breaks the assumption that a green clean clone and a green worktree mean the same thing.

Suspected fix

• Run the git-learning fixture against an isolated temp repo / temp GIT_DIR, not the live checkout.
• Audit the test for any implicit cwd assumptions.

Nice-to-have

• Add a regression test that proves the active repo HEAD does not change after the git-learning test runs.