fix(result): avoid mutating errors when pickling task results

taskiq/result/result.py

@@ -55,16 +55,17 @@ def raise_for_error(self) -> "Self":
         return self
 
     def __getstate__(self) -> dict[Any, Any]:
-        dict = super().__getstate__()
-        vals: builtins.dict[str, Any] = dict["__dict__"]
+        state = super().__getstate__()
+        vals: builtins.dict[str, Any] = state["__dict__"].copy()
+        state["__dict__"] = vals
 
         if "error" in vals and vals["error"] is not None:
             vals["error"] = prepare_exception(
                 vals["error"],
                 pickle,
             )
 
-        return dict
+        return state
 
     @field_validator("error", mode="before")
     @classmethod

tests/test_result.py

@@ -64,6 +64,30 @@ def test_pickle_error_serialization() -> None:
     assert type(data.error) == type(task.error)  # noqa: E721
 
 
+def test_pickle_unpickleable_error_does_not_mutate_result() -> None:
+    class LocalError(Exception):
+        pass
+
+    error = LocalError("boom")
+    result: TaskiqResult[None] = TaskiqResult(
+        is_err=True,
+        return_value=None,
+        execution_time=0,
+        error=error,
+    )
+
+    serialized = pickle.dumps(result)
+
+    restored = pickle.loads(serialized)
+    assert restored.is_err
+    assert isinstance(restored.error, BaseException)
+    assert str(restored.error) == repr(error)
+    assert result.error is error
+    with pytest.raises(LocalError) as exc:
+        result.raise_for_error()
+    assert exc.value is error
+
+
 def test_result_raise_for_error_exc() -> None:
     error = ValueError("Error")
     res: TaskiqResult[None] = TaskiqResult(