Reject non-string atomic text writes (#1819)

core/atomic_io.py

@@ -34,6 +34,8 @@ def atomic_write_json(path: str, data: Any, *, indent: Optional[int] = None) ->
 
 
 def atomic_write_text(path: str, text: str) -> None:
+    if not isinstance(text, str):
+        raise TypeError("atomic_write_text expects a string")
     os.makedirs(os.path.dirname(path) or ".", exist_ok=True)
     tmp = f"{path}.tmp.{os.getpid()}"
     with open(tmp, "w", encoding="utf-8") as f:

tests/test_atomic_io.py

@@ -138,6 +138,16 @@ def test_atomic_write_text_leaves_no_tmp_file(tmp_path):
     assert _tmp_siblings(tmp_path, "note.txt") == []
 
 
+def test_atomic_write_text_rejects_non_string_before_tmp_file(tmp_path):
+    target = tmp_path / "note.txt"
+
+    with pytest.raises(TypeError):
+        atomic_write_text(str(target), 123)
+
+    assert not target.exists()
+    assert _tmp_siblings(tmp_path, "note.txt") == []
+
+
 # ---------------------------------------------------------------------------
 # atomic_write_text — failure path: target preserved when replace fails.
 # ---------------------------------------------------------------------------