[Bugfix] Fix cross-request codes.ref leak in Qwen3-TTS make_omni_output (#4373)

Signed-off-by: jjw <m@jjw.in>
Co-authored-by: jjw <m@jjw.in>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Yueqian Lin <70319226+linyueqian@users.noreply.github.com>

tests/model_executor/models/qwen3_tts/test_qwen3_tts_talker_ref_codes.py

@@ -0,0 +1,76 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Regression tests for cross-request ``codes.ref`` leakage (#4370).
+
+``make_omni_output`` used to collapse every request's reference codec
+frames into a single last-writer-wins slot and emit it as a length-1
+list. ``to_payload_element`` indexes list payloads with
+``element[idx] if idx < len(element) else element[0]``, so that length-1
+list was broadcast to every request in the batch: each utterance's first
+vocoder chunks then decoded with another request's reference voice as
+context (audible onset timbre deformation at any concurrency > 1).
+"""
+
+import pytest
+import torch
+
+from vllm_omni.model_executor.models.qwen3_tts.qwen3_tts_talker import (
+    Qwen3TTSTalkerForConditionalGeneration,
+)
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+_NUM_CODE_GROUPS = 16
+
+
+def _make_talker() -> Qwen3TTSTalkerForConditionalGeneration:
+    # make_omni_output reads no instance state, so skip __init__ (no real
+    # config / checkpoint needed), same as the preprocess tests.
+    return Qwen3TTSTalkerForConditionalGeneration.__new__(Qwen3TTSTalkerForConditionalGeneration)
+
+
+def _info(span_frames: int, ref_code: torch.Tensor | None) -> dict:
+    codes: dict = {"audio": torch.zeros((span_frames, _NUM_CODE_GROUPS), dtype=torch.long)}
+    meta: dict = {}
+    if ref_code is not None:
+        codes["ref"] = ref_code
+        meta["ref_code_len"] = int(ref_code.shape[0])
+    return {"codes": codes, "meta": meta}
+
+
+def test_make_omni_output_keeps_ref_codes_per_request() -> None:
+    ref_a = torch.ones((3, _NUM_CODE_GROUPS), dtype=torch.long)
+    ref_b = torch.full((5, _NUM_CODE_GROUPS), 2, dtype=torch.long)
+
+    out = _make_talker().make_omni_output(
+        torch.zeros((4, 8)),
+        model_intermediate_buffer=[_info(2, ref_a), _info(2, ref_b)],
+    )
+
+    ref_list = out.multimodal_outputs["codes"]["ref"]
+    assert len(ref_list) == 2, "codes.ref must stay batch-aligned (one entry per request)"
+    assert torch.equal(ref_list[0], ref_a)
+    assert torch.equal(ref_list[1], ref_b)
+
+
+def test_make_omni_output_pads_requests_without_ref_code() -> None:
+    ref_b = torch.full((5, _NUM_CODE_GROUPS), 2, dtype=torch.long)
+
+    out = _make_talker().make_omni_output(
+        torch.zeros((4, 8)),
+        model_intermediate_buffer=[_info(2, None), _info(2, ref_b)],
+    )
+
+    ref_list = out.multimodal_outputs["codes"]["ref"]
+    assert len(ref_list) == 2
+    assert ref_list[0].numel() == 0, "no-ref request must get an empty placeholder, not a neighbor's ref"
+    assert torch.equal(ref_list[1], ref_b)
+
+
+def test_make_omni_output_omits_ref_key_when_no_request_has_one() -> None:
+    out = _make_talker().make_omni_output(
+        torch.zeros((4, 8)),
+        model_intermediate_buffer=[_info(2, None), _info(2, None)],
+    )
+
+    assert "ref" not in out.multimodal_outputs["codes"]