Lift drill into evals/ at 013fcb8b7dbefd6d3fa4653493e5d2ec8e7f985b

rsync of obra/drill@013fcb8b7d into superpowers/evals/, excluding
.git/, .venv/, results/, .env/, __pycache__/, *.egg-info/,
.private-journal/.

The drill repo is unaffected by this commit; archival is a separate
manual step after this PR merges.

Source SHA recorded at evals/.drill-source-sha for divergence
detection.

evals/setup_helpers/worktree.py

@@ -0,0 +1,130 @@
+from __future__ import annotations
+import json
+import subprocess
+from pathlib import Path
+
+from setup_helpers.base import _git
+
+
+CALLER_CONSENT_PLAN = """\
+# Custom Greeting Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development
+> or superpowers:executing-plans to implement this plan task-by-task.
+
+**Goal:** Add a small greeting customization feature to the Node fixture.
+
+---
+
+### Task 1: Custom greeting
+
+**Files:**
+- Modify: `src/index.js`
+- Modify: `src/utils.js`
+- Create: `tests/greeting.test.js`
+
+**Acceptance Criteria:**
+- The app can greet a provided name instead of always greeting `world`.
+- The default behavior remains `Hello, world!`.
+- A test covers both the default and custom-name paths.
+
+- [ ] **Step 1: Add tests for default and custom greetings.**
+- [ ] **Step 2: Update the greeting implementation.**
+- [ ] **Step 3: Run the relevant tests.**
+"""
+
+
+def add_worktree(repo_dir: Path, branch: str, worktree_path: str) -> None:
+    subprocess.run(
+        ["git", "worktree", "add", "-b", branch, worktree_path],
+        cwd=repo_dir, check=True, capture_output=True,
+    )
+
+
+def detach_head(worktree_path: str) -> None:
+    result = subprocess.run(
+        ["git", "rev-parse", "HEAD"], cwd=worktree_path,
+        capture_output=True, text=True, check=True,
+    )
+    commit = result.stdout.strip()
+    result = subprocess.run(
+        ["git", "branch", "--show-current"], cwd=worktree_path,
+        capture_output=True, text=True, check=True,
+    )
+    branch = result.stdout.strip()
+    subprocess.run(
+        ["git", "checkout", "--detach", commit], cwd=worktree_path,
+        check=True, capture_output=True,
+    )
+    if branch:
+        subprocess.run(
+            ["git", "branch", "-D", branch], cwd=worktree_path,
+            capture_output=True,
+        )
+
+
+def add_existing_worktree(workdir: Path) -> None:
+    """Create an existing worktree (for 'already inside' scenarios)."""
+    wt_path = workdir.parent / f"{workdir.name}-existing-worktree"
+    add_worktree(workdir, "existing-feature", str(wt_path))
+
+
+def detach_worktree_head(workdir: Path) -> None:
+    """Detach HEAD in the existing worktree."""
+    wt_path = workdir.parent / f"{workdir.name}-existing-worktree"
+    detach_head(str(wt_path))
+
+
+def symlink_superpowers(workdir: Path, superpowers_root: str) -> None:
+    skills_dir = Path(workdir) / ".agents" / "skills"
+    skills_dir.mkdir(parents=True, exist_ok=True)
+    target = Path(superpowers_root) / "skills"
+    link = skills_dir / "superpowers"
+    link.symlink_to(target)
+
+
+def link_gemini_extension(workdir: Path, superpowers_root: str) -> None:
+    """Link superpowers as a Gemini CLI extension and inject project context.
+
+    Extensions are global, but GEMINI.md context loading is project-scoped.
+    Temp workdirs need a GEMINI.md with absolute paths so Gemini loads
+    the using-superpowers instructions that tell it to invoke skills.
+    """
+    extension_name = "superpowers"
+    manifest = Path(superpowers_root) / "gemini-extension.json"
+    if manifest.exists():
+        try:
+            extension_name = json.loads(manifest.read_text()).get("name", extension_name)
+        except json.JSONDecodeError:
+            pass
+
+    # Gemini extensions are global; replace any prior link so this run tests
+    # the requested SUPERPOWERS_ROOT checkout rather than a stale install.
+    subprocess.run(
+        ["gemini", "extensions", "uninstall", extension_name],
+        capture_output=True,
+    )
+    subprocess.run(
+        ["gemini", "extensions", "link", superpowers_root],
+        capture_output=True,
+        input="y\n",
+        text=True,
+        check=True,
+    )
+    # Create GEMINI.md with absolute @imports so context loads in the temp workdir
+    skills_root = Path(superpowers_root) / "skills"
+    gemini_md = workdir / "GEMINI.md"
+    gemini_md.write_text(
+        f"@{skills_root}/using-superpowers/SKILL.md\n"
+        f"@{skills_root}/using-superpowers/references/gemini-tools.md\n"
+    )
+
+
+def create_caller_consent_plan(workdir: Path) -> None:
+    """Add a committed implementation plan that should trigger caller-layer gating."""
+    plan_path = workdir / "docs" / "superpowers" / "plans" / "custom-greeting.md"
+    plan_path.parent.mkdir(parents=True, exist_ok=True)
+    plan_path.write_text(CALLER_CONSENT_PLAN)
+
+    _git(["git", "add", str(plan_path.relative_to(workdir))], cwd=workdir)
+    _git(["git", "commit", "-m", "add caller consent gate plan"], cwd=workdir)