fix: do not apply FP8 quant config to vision/audio encoders for pre-quantized checkpoints (#2702)

Signed-off-by: Yiyang Liu <37043548+ianliuy@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/model_executor/models/test_encoder_quant_config.py

@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Regression test for #2686: pre-quantized methods must not apply
+quant config to vision / audio encoders.
+
+For modelopt FP8/FP4/MXFP8 checkpoints the Thinker LM is the only
+quantized component.  Vision and audio encoder weights are BF16 with no
+FP8 scale tensors — passing quant_config to them causes FP8 kernels to
+run on BF16 weights, producing garbage embeddings.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+import pytest
+
+from vllm_omni.quantization.component_config import (
+    PRE_QUANTIZED_METHODS,
+    ComponentQuantizationConfig,
+    resolve_encoder_quant_config,
+)
+
+pytestmark = [pytest.mark.core_model, pytest.mark.cpu]
+
+# ---------------------------------------------------------------------------
+# resolve_encoder_quant_config — the core routing logic for encoder quant
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.parametrize("method", sorted(PRE_QUANTIZED_METHODS))
+def test_pre_quantized_returns_none(method: str) -> None:
+    """visual_quant_config and audio_quant_config must be None for
+    pre-quantized methods (modelopt, modelopt_fp4, modelopt_mxfp8)."""
+    mock_config = MagicMock()
+    mock_config.get_name.return_value = method
+
+    assert resolve_encoder_quant_config(mock_config) is None
+
+
+@pytest.mark.parametrize("method", ["fp8", "awq", "gptq", "bitsandbytes"])
+def test_non_pre_quantized_preserves_config(method: str) -> None:
+    """Non-pre-quantized methods should pass through the original config."""
+    mock_config = MagicMock()
+    mock_config.get_name.return_value = method
+
+    assert resolve_encoder_quant_config(mock_config) is mock_config
+
+
+def test_none_input_returns_none() -> None:
+    """No quantization → None for encoders."""
+    assert resolve_encoder_quant_config(None) is None
+
+
+def test_component_config_passed_through() -> None:
+    """ComponentQuantizationConfig should be returned as-is so the caller
+    can call .resolve() with the appropriate prefix."""
+    inner = MagicMock()
+    inner.get_name.return_value = "modelopt"  # would be None if not Component
+    component = ComponentQuantizationConfig(
+        component_configs={"language_model": inner},
+        default_config=None,
+    )
+
+    result = resolve_encoder_quant_config(component)
+    assert result is component
+
+
+# ---------------------------------------------------------------------------
+# PRE_QUANTIZED_METHODS constant — exhaustiveness check
+# ---------------------------------------------------------------------------
+
+
+def test_pre_quantized_methods_contains_expected() -> None:
+    """Guard against accidental removal of a known pre-quantized method."""
+    expected = {"modelopt", "modelopt_fp4", "modelopt_mxfp8"}
+    assert PRE_QUANTIZED_METHODS == expected