[Bugfix][RAINFUSION_ATTN] Fix padding-mask rejection on packed [real, pad] layouts and reuse query tail as output padding (#7235)

Signed-off-by: brandneway <gyuan4892@gmail.com>

tests/diffusion/attention/test_mindie_runtime.py

@@ -193,7 +193,11 @@ def test_sparse_quant_uses_public_runtime(runtime, monkeypatch, method):
     monkeypatch.setattr(rainfusion_attn, "_mindiesd_supports_precision", lambda: True)
     q = torch.randn(1, 4224, 2, 64, dtype=torch.bfloat16)
     out = sparse().forward_npu(q, q, q, video_metadata(kv_cache_dtype=method))
-    assert out.shape == q.shape and not out[:, 4096:].any()
+    # The sparse path reuses the query tail as the output padding instead of
+    # zero-filling a fresh buffer; rows past the 4096-row valid prefix are
+    # never read back downstream (the model unpads by cu_seqlens), so pin the
+    # passthrough rather than requiring zeros.
+    assert out.shape == q.shape and torch.equal(out[:, 4096:], q[:, 4096:])
     kwargs = runtime.sparse_attention.call_args.kwargs
     assert (kwargs["precision"], kwargs["sparse_type"], kwargs["inner_precise"]) == (method, "rf_v3", 4)
     runtime.quant_attention.assert_not_called()