Isolate tmp-dependent tests from ambient git

[starr-openai]

Stack:

• PR #22199 Isolate tmp-dependent tests from ambient git
• PR #22201 Use remote fs for turn diff repo root
• PR #22200 Emit unified exec end on startup failure
• PR #22202 Stabilize remote routing e2e tests

Summary:

• isolate project-root-sensitive test fixtures from ambient /tmp git metadata
• keep the fix scoped to core-skills, secrets, and TUI tests

Testing:

• Ran just fmt; not running tests locally for this Codex PR.