[BugFix][Qwen-Image] align txt_seq_lens RoPE width with padded embeds (#4474)

Signed-off-by: samithuang <285365963@qq.com>

tests/diffusion/test_input_batch_txt_seq_lens.py

@@ -0,0 +1,31 @@
+import pytest
+import torch
+
+from vllm_omni.diffusion.worker.input_batch import _prepare_request_prompt_field
+from vllm_omni.diffusion.worker.utils import DiffusionRequestState
+from vllm_omni.inputs.data import OmniDiffusionSamplingParams
+
+pytestmark = [pytest.mark.cpu]
+
+
+def test_prepare_request_prompt_field_refreshes_txt_seq_lens_after_padding():
+    state = DiffusionRequestState(
+        request_id="req-0",
+        sampling=OmniDiffusionSamplingParams(),
+        prompt_embeds=torch.randn(1, 10, 4),
+        prompt_embeds_mask=torch.ones(1, 10, dtype=torch.bool),
+        txt_seq_lens=[10],
+    )
+
+    embeds, mask = _prepare_request_prompt_field(
+        state,
+        embeds_attr="prompt_embeds",
+        mask_attr="prompt_embeds_mask",
+        seq_lens_attr="txt_seq_lens",
+        target_seq_len=32,
+    )
+
+    assert embeds.shape == (1, 32, 4)
+    assert mask is not None and mask.shape == (1, 32)
+    assert state.txt_seq_lens == [32]
+    assert mask.sum(dim=1).tolist() == [10]