fix: do not follow ../ refs out of the project

src/shotbible/check.py

@@ -214,10 +214,15 @@ def _listed_refs(bible: Bible) -> set[str]:
 def _ref_exists(root: Path, ref: str) -> bool:
     if not str(ref).strip():
         return False
+    root = root.resolve()
     path = Path(ref)
-    if path.is_absolute():
-        return path.exists()
-    return (root / ref).exists()
+    candidate = path if path.is_absolute() else root / ref
+    try:
+        resolved = candidate.resolve()
+        resolved.relative_to(root)
+    except (ValueError, OSError):
+        return False
+    return candidate.exists()
 
 
 def _normalize_look(look: str) -> str:

tests/test_ref_escape.py

@@ -0,0 +1,32 @@
+from pathlib import Path
+
+from shotbible.check import check_bible
+from shotbible.store import save
+
+from conftest import make_sample_bible, write_dummy_png
+
+
+def test_check_rejects_relative_path_escape(tmp_path: Path) -> None:
+    root = tmp_path / "escape"
+    root.mkdir()
+    outside = tmp_path / "outside.png"
+    write_dummy_png(outside)
+    bible = make_sample_bible(with_ref=False)
+    bible.characters["mei"].refs = ["../outside.png"]
+    save(root, bible)
+
+    issues = check_bible(root, bible)
+    assert any(getattr(issue, "code", None) == "MISSING_REF" for issue in issues)
+
+
+def test_check_rejects_absolute_path_outside_project(tmp_path: Path) -> None:
+    root = tmp_path / "abs"
+    root.mkdir()
+    outside = tmp_path / "outside.png"
+    write_dummy_png(outside)
+    bible = make_sample_bible(with_ref=False)
+    bible.characters["mei"].refs = [str(outside.resolve())]
+    save(root, bible)
+
+    issues = check_bible(root, bible)
+    assert any(getattr(issue, "code", None) == "MISSING_REF" for issue in issues)