feat: gate mask_from_stash (paint or zeros)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

gates/gate.py

@@ -13,3 +13,12 @@ MAX_ROUTES = 10
 
 def route_tuple(chosen, image, blocker, max_routes=MAX_ROUTES):
     return tuple(image if i == chosen else blocker for i in range(max_routes))
+
+
+def mask_from_stash(data, image):
+    b, h, w = image.shape[0], image.shape[1], image.shape[2]
+    if not data:
+        return torch.zeros((b, h, w), dtype=torch.float32)
+    m = Image.open(io.BytesIO(data)).convert("L")
+    arr = np.array(m, dtype=np.float32) / 255.0
+    return torch.from_numpy(arr).unsqueeze(0)

tests/test_gate.py

@@ -1,4 +1,9 @@
 # tests/test_gate.py
+import io
+
+import torch
+from PIL import Image
+
 from gates import gate
 
 def test_route_tuple_places_image_at_chosen():
@@ -9,3 +14,14 @@ def test_route_tuple_places_image_at_chosen():
 def test_route_tuple_length_is_max():
     B = object()
     assert len(gate.route_tuple(0, "IMG", B, max_routes=10)) == 10
+
+def test_mask_from_stash_none_is_zeros():
+    img = torch.zeros((1, 6, 4, 3))
+    m = gate.mask_from_stash(None, img)
+    assert m.shape == (1, 6, 4) and float(m.max()) == 0.0
+
+def test_mask_from_stash_decodes_png():
+    buf = io.BytesIO(); Image.new("L", (4, 6), 255).save(buf, "PNG")
+    img = torch.zeros((1, 6, 4, 3))
+    m = gate.mask_from_stash(buf.getvalue(), img)
+    assert m.shape == (1, 6, 4) and float(m.min()) > 0.99