[diffusion] chore: reuse srt siglip vision model (#34988)

test/registered/unit/layers/attention/test_vision_backend_selection.py

@@ -52,6 +52,39 @@ def test_npu_backend_selection_priority(
     assert backend == expected
 
 
+def test_explicit_backend_without_published_mm_context(monkeypatch, npu_platform):
+    monkeypatch.setattr(
+        vision,
+        "get_mm",
+        Mock(side_effect=ValueError("config namespace 'mm' not published")),
+    )
+    monkeypatch.setattr(
+        vision,
+        "get_context",
+        lambda: SimpleNamespace(is_config_namespace_published=lambda namespace: False),
+    )
+
+    backend = vision.VisionAttention._determine_attention_backend(None, "sdpa")
+
+    assert backend == "sdpa"
+
+
+def test_explicit_backend_keeps_published_context_errors(monkeypatch, npu_platform):
+    monkeypatch.setattr(
+        vision,
+        "get_mm",
+        Mock(side_effect=ValueError("mm namespace is not available for this role")),
+    )
+    monkeypatch.setattr(
+        vision,
+        "get_context",
+        lambda: SimpleNamespace(is_config_namespace_published=lambda namespace: True),
+    )
+
+    with pytest.raises(ValueError, match="not available for this role"):
+        vision.VisionAttention._determine_attention_backend(None, "sdpa")
+
+
 def test_sdpa_preserves_flattened_batch_layout():
     torch.manual_seed(0)
     bsz, seq_len, num_heads, head_dim = 3, 5, 2, 8