fix(v5): reconstruct inverse fft from saved spectrum

backend/processing/storage.py

@@ -30,6 +30,14 @@ def save_image_array(image, prefix="image"):
     return filename
 
 
+def save_fft_array(spectrum, prefix="fft"):
+    filename = f"sessions/{prefix}-{uuid4().hex}.npz"
+    path = Path(settings.MEDIA_ROOT) / filename
+    path.parent.mkdir(parents=True, exist_ok=True)
+    np.savez_compressed(path, spectrum=spectrum)
+    return filename
+
+
 def load_image_array(relative_path):
     path = Path(settings.MEDIA_ROOT) / relative_path
     if not path.exists():
@@ -45,6 +53,17 @@ def load_image_array(relative_path):
     return cv2.cvtColor(image, cv2.COLOR_BGR2RGB).astype(np.uint8)
 
 
+def load_fft_array(relative_path):
+    path = Path(settings.MEDIA_ROOT) / relative_path
+    if not path.exists():
+        raise ProcessingError("FFT data file is missing or unreadable.")
+    try:
+        with np.load(path) as payload:
+            return payload["spectrum"]
+    except (OSError, KeyError, ValueError) as exc:
+        raise ProcessingError("FFT data file is missing or unreadable.") from exc
+
+
 def delete_relative_file(relative_path):
     if not relative_path:
         return