Fix: prevent tag assignment from reverting other pending workflow assignments (#13178)

apply_assignment_to_document() mutated tags directly on the shared document instance via add_nested_tags(), whose m2m_changed signal triggers update_filename_and_move_files() -> instance.refresh_from_db(), discarding any not-yet-saved fields (e.g. storage_path) staged by an earlier-ordered action in the same workflow. Apply tag changes to a freshly-fetched instance instead, matching the pattern already used in apply_removal_to_document().

src/documents/tests/test_workflows.py

@@ -2938,6 +2938,69 @@ class TestWorkflows(
         self.assertFalse(doc.tags.filter(pk=self.t1.pk).exists())
         self.assertTrue(doc.tags.filter(pk=self.t2.pk).exists())
 
+    def test_document_updated_workflow_assignment_storage_path_persists_with_tag_assignment(
+        self,
+    ) -> None:
+        """
+        GIVEN:
+            - A document updated workflow filtered on a tag
+            - One assignment action assigns a storage path, a second (later-ordered)
+              assignment action adds a tag
+        WHEN:
+            - The document is updated and the workflow is triggered
+        THEN:
+            - Both the tag and the storage path are persisted
+        """
+        trigger = WorkflowTrigger.objects.create(
+            type=WorkflowTrigger.WorkflowTriggerType.DOCUMENT_UPDATED,
+        )
+        trigger.filter_has_tags.add(self.t1)
+        assign_storage_path = WorkflowAction.objects.create(
+            type=WorkflowAction.WorkflowActionType.ASSIGNMENT,
+            assign_storage_path=self.sp,
+            order=0,
+        )
+        assign_tag = WorkflowAction.objects.create(
+            type=WorkflowAction.WorkflowActionType.ASSIGNMENT,
+            order=1,
+        )
+        assign_tag.assign_tags.add(self.t2)
+        assign_tag.save()
+
+        workflow = Workflow.objects.create(
+            name="Workflow assign storage path then tag",
+            order=0,
+        )
+        workflow.triggers.add(trigger)
+        workflow.actions.add(assign_storage_path, assign_tag)
+        workflow.save()
+
+        doc = Document.objects.create(
+            title="sample test",
+            mime_type="application/pdf",
+            checksum="assign-tag-and-storage-path",
+            original_filename="sample.pdf",
+        )
+        generated = generate_unique_filename(doc)
+        destination = (settings.ORIGINALS_DIR / generated).resolve()
+        create_source_path_directory(destination)
+        shutil.copy(self.SAMPLE_DIR / "simple.pdf", destination)
+        Document.objects.filter(pk=doc.pk).update(filename=generated.as_posix())
+        doc.refresh_from_db()
+        doc.tags.set([self.t1])
+
+        superuser = User.objects.create_superuser("superuser")
+        self.client.force_authenticate(user=superuser)
+        self.client.patch(
+            f"/api/documents/{doc.id}/",
+            {"title": "user update to trigger workflow"},
+            format="json",
+        )
+
+        doc.refresh_from_db()
+        self.assertEqual(doc.storage_path, self.sp)
+        self.assertTrue(doc.tags.filter(pk=self.t2.pk).exists())
+
     def test_removal_action_document_updated_removeall(self) -> None:
         """
         GIVEN:

src/documents/workflows/mutations.py

@@ -24,7 +24,11 @@ def apply_assignment_to_document(
     action: WorkflowAction, annotated with 'has_assign_*' boolean fields
     """
     if action.has_assign_tags:
-        document.add_nested_tags(action.assign_tags.all())
+        # Apply to a freshly-fetched instance rather than the shared `document`.
+        # Document.tags.add() fires an m2m_changed signal that ultimately calls
+        # instance.refresh_from_db(), which would discard any other unsaved
+        # assignment fields (e.g. storage_path) already staged on `document`.
+        Document.objects.get(pk=document.pk).add_nested_tags(action.assign_tags.all())
 
     if action.assign_correspondent:
         document.correspondent = action.assign_correspondent