Merge latest feature/puzzletron_v2 into PR 2125 branch

Signed-off-by: Johannes Rausch <jrausch@nvidia.com>

Author: j-rausch

tests/unit/torch/puzzletron/test_setup_v2_state.py

@@ -0,0 +1,47 @@
+# SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Failure-path tests for atomic PuzzleTron v2 wizard state persistence."""
+
+from __future__ import annotations
+
+import pytest
+
+from puzzletron_setup import SetupError
+from puzzletron_setup.v2 import state as state_module
+from puzzletron_setup.v2.state import WizardState
+
+
+def test_failed_atomic_replace_preserves_last_resumable_state(tmp_path, monkeypatch):
+    state = WizardState.start(tmp_path / "campaign", defaults_path=None)
+    state.set_field("model.source", "/models/teacher")
+    durable_snapshot = state.path.read_bytes()
+    real_replace = state_module.os.replace
+    replace_targets = []
+
+    def fail_replace(source, destination):
+        replace_targets.append(destination)
+        if destination == state.path:
+            raise OSError("injected replace failure")
+        return real_replace(source, destination)
+
+    monkeypatch.setattr(state_module.os, "replace", fail_replace)
+
+    with pytest.raises(SetupError, match="Cannot save v2 setup state"):
+        state.set_field("model.source", "/models/candidate")
+
+    assert state.path in replace_targets
+    assert state.path.read_bytes() == durable_snapshot
+    assert WizardState.resume(state.path).get_field("model.source") == "/models/teacher"