fix: write back exchange json beside qet input

src/Mod/FreeCADExchange/ExchangeWriteBack.py

@@ -17,6 +17,7 @@ except ImportError:
 
 
 STATE_WRITEBACK_OBSERVER = "_qet_exchange_writeback_observer"
+ENV_JSON_PATH = "QET_2D_TO_3D_JSON"
 
 
 class ExchangeWriteBackError(RuntimeError):
@@ -110,6 +111,13 @@ def _output_path_for_scene(scene_path):
     return str(path.parent / "3d_to_2d.json")
 
 
+def _output_path_for_exchange_json():
+    json_path = os.environ.get(ENV_JSON_PATH, "").strip()
+    if not json_path:
+        return ""
+    return str(Path(json_path).with_name("3d_to_2d.json"))
+
+
 def _format_timestamp():
     return datetime.now().astimezone().isoformat(timespec="seconds")
 
@@ -174,7 +182,7 @@ def write_back_document(doc=None, scene_path="", payload=None):
         raise ExchangeWriteBackError("No active FreeCAD document is available.")
 
     scene_path = _scene_path_from_doc(doc, scene_path)
-    output_path = _output_path_for_scene(scene_path)
+    output_path = _output_path_for_exchange_json() or _output_path_for_scene(scene_path)
     if not output_path:
         raise ExchangeWriteBackError(
             "Cannot determine the 3d_to_2d.json output path."

tests/python/freecad_exchange_wiring_test.py

@@ -1,4 +1,6 @@
+import os
 import sys
+import tempfile
 import types
 import unittest
 from pathlib import Path
@@ -364,6 +366,40 @@ class WiringTest(unittest.TestCase):
 
         self.assertNotIn("manual_wires", report)
 
+    def test_writeback_prefers_qet_exchange_json_directory_over_scene_directory(self):
+        _install_fake_freecad()
+        terminal_objects, _wiring_objects, _manual_wiring, write_back = _reload_modules()
+
+        doc = FakeDocument()
+        terminal_objects.ensure_root_group(doc, "project-1")
+
+        old_scene = os.environ.get("QET_FREECAD_SCENE_FILE")
+        old_json = os.environ.get("QET_2D_TO_3D_JSON")
+        try:
+            with tempfile.TemporaryDirectory() as tmp_dir:
+                tmp_path = Path(tmp_dir)
+                scene_dir = tmp_path / "3D"
+                exchange_dir = tmp_path / ".qet_freecad"
+                scene_dir.mkdir()
+                exchange_dir.mkdir()
+                os.environ["QET_FREECAD_SCENE_FILE"] = str(scene_dir / "current.FCStd")
+                os.environ["QET_2D_TO_3D_JSON"] = str(exchange_dir / "2d_to_3d.json")
+
+                report = write_back.write_back_document(doc, payload={"project_uuid": "project-1"})
+
+                self.assertEqual(str(exchange_dir / "3d_to_2d.json"), report["output_path"])
+                self.assertTrue((exchange_dir / "3d_to_2d.json").is_file())
+                self.assertFalse((scene_dir / "3d_to_2d.json").exists())
+        finally:
+            if old_scene is None:
+                os.environ.pop("QET_FREECAD_SCENE_FILE", None)
+            else:
+                os.environ["QET_FREECAD_SCENE_FILE"] = old_scene
+            if old_json is None:
+                os.environ.pop("QET_2D_TO_3D_JSON", None)
+            else:
+                os.environ["QET_2D_TO_3D_JSON"] = old_json
+
 
 if __name__ == "__main__":
     unittest.main()