fix(vision): reference image sopravvive al copy-on-write (#38.6)

_copy_tasks_to_version non copiava le righe VisionReferenceImage del
task sorgente: il task copiato perdeva le immagini di riferimento del
grafo di visione. Ora copia le righe sul task nuovo, stesso path e
stessi metadati (stesso file su disco, non duplicato).
Di conseguenza il file va cancellato solo se nessun'altra riga
VisionReferenceImage referenzia lo stesso path: nuova
vision_service.file_still_referenced(), usata dalla route DELETE
prima di remove_reference_file.
Test: copy-on-write elenca l'immagine sulla nuova versione; DELETE di
una delle due righe lascia il file; DELETE dell'ultima lo rimuove.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/backend/services/recipe_service.py

@@ -12,6 +12,7 @@ from src.backend.models.orm.recipe import Recipe, RecipeVersion
 from src.backend.models.orm.setting import RecipeVersionAudit
 from src.backend.models.orm.task import RecipeSubtask, RecipeTask
 from src.backend.models.orm.user import User
+from src.backend.models.orm.vision import VisionReferenceImage
 from src.backend.models.api.recipe import RecipeCreate, RecipeUpdate
 
 
@@ -118,6 +119,28 @@ async def _copy_tasks_to_version(
         db.add(new_task)
         await db.flush()  # get new_task.id
 
+        # Reference images (#38.6): the copied task points at the same files
+        # on disk as the source - same `path`, same acquisition metadata. A
+        # graph composed against a reference must keep working after the
+        # recipe is next edited, exactly like task_type/vision_json above.
+        # The file itself is only ever removed once no row references its
+        # path any more (see vision_service.file_still_referenced).
+        ref_images = (await db.execute(
+            select(VisionReferenceImage).where(VisionReferenceImage.task_id == task.id)
+        )).scalars().all()
+        for ref in ref_images:
+            db.add(VisionReferenceImage(
+                task_id=new_task.id,
+                path=ref.path,
+                station_id=ref.station_id,
+                device_code=ref.device_code,
+                calibration_snapshot=ref.calibration_snapshot,
+                engine_version=ref.engine_version,
+                note=ref.note,
+                expected_json=ref.expected_json,
+                acquired_at=ref.acquired_at,
+            ))
+
         for sub in task.subtasks:
             new_sub = RecipeSubtask(
                 task_id=new_task.id,

src/backend/services/vision_service.py

@@ -275,6 +275,22 @@ def remove_reference_file(reference: VisionReferenceImage) -> None:
     _reference_file_path(reference).unlink(missing_ok=True)
 
 
+async def file_still_referenced(db: AsyncSession, path: str) -> bool:
+    """True if some VisionReferenceImage row still points at *path*.
+
+    Copy-on-write (#38.6) can leave several rows sharing the same file on
+    disk (the copy carries over the source's `path` rather than duplicating
+    the file). The router must call this, after the row being deleted has
+    been committed, before it calls `remove_reference_file` - otherwise
+    deleting one task's reference would take the file out from under every
+    other task that still references it.
+    """
+    result = await db.execute(
+        select(VisionReferenceImage.id).where(VisionReferenceImage.path == path).limit(1)
+    )
+    return result.scalar_one_or_none() is not None
+
+
 async def save_reference_image(
     db: AsyncSession,
     task_id: int,