feat: isolate agentic worktrees and surface execution evidence

cross_eval/worktree.py

@@ -4,6 +4,7 @@ from __future__ import annotations
 import logging
 import shutil
 import subprocess
+import tempfile
 from datetime import datetime
 from pathlib import Path
 
@@ -20,6 +21,22 @@ def make_branch_name(preset_name: str) -> str:
     return f"cross-eval/{preset_name}_{ts}"
 
 
+def make_worktree_dir(base_cwd: Path, branch_name: str) -> Path:
+    """Choose a worktree directory outside the base repo.
+
+    Keeping agentic worktrees outside the source checkout avoids tools that
+    incorrectly walk up to the outer repo and write into the base worktree.
+    """
+    repo_name = base_cwd.resolve().name or "repo"
+    branch_slug = branch_name.replace("/", "__")
+    return (
+        Path(tempfile.gettempdir())
+        / "cross-eval-worktrees"
+        / repo_name
+        / branch_slug
+    )
+
+
 def create_worktree(base_cwd: Path, work_dir: Path, branch_name: str) -> Path:
     """Create a git worktree on a new branch from HEAD.