Unskip FP8 Z-Image quality case

Signed-off-by: WeiQing Chen <david6666666@users.noreply.github.com>

tests/diffusion/quantization/artifacts/fp8_z_image_quality/README.md

@@ -0,0 +1,29 @@
+# FP8 Z-Image Quality Artifact
+
+Generated by:
+
+```bash
+CUDA_VISIBLE_DEVICES=0 \
+VLLM_OMNI_QUALITY_OUTPUT_DIR=$PWD/tests/diffusion/quantization/artifacts/fp8_z_image_quality \
+.venv/bin/python -m pytest \
+  tests/diffusion/quantization/test_quantization_quality.py::test_quantization_quality[fp8_z_image] \
+  -s -v -m ""
+```
+
+Result: failed with the current `max_lpips=0.15` threshold.
+
+| Metric | Value |
+|--------|-------|
+| LPIPS | 0.250578 |
+| PSNR | 17.042153 dB |
+| MAE | 0.076899 |
+
+## Comparison
+
+![BF16 baseline vs FP8 quantized](fp8_z_image_comparison.png)
+
+## Individual Outputs
+
+![BF16 baseline](fp8_z_image_baseline.png)
+
+![FP8 quantized](fp8_z_image_quantized.png)

tests/diffusion/quantization/test_quantization_quality.py

@@ -120,7 +120,27 @@ QUALITY_CONFIGS = [
         model="Tongyi-MAI/Z-Image-Turbo",
         quantization="fp8",
         task="t2i",
-        prompt="a cup of coffee on a wooden table, morning light",
+        prompt=(
+            "A breathtaking twilight scene atop a floating archipelago of crystalline islands suspended in an "
+            "endless nebula-drenched sky, where waterfalls of liquid starlight cascade from the edges of each "
+            "island into the cosmic abyss below. The largest island hosts an ancient, overgrown observatory "
+            "crafted from pearlescent white stone and living silverwood trees whose bioluminescent leaves pulse "
+            "with soft cerulean and violet light. At the observatory's center stands a solitary figure—a young "
+            "astronomer in flowing robes woven from woven moonlight and deep-space fabric, their face illuminated "
+            "by the glow of a holographic star chart hovering above an altar of polished obsidian. The sky swirls "
+            "with the birth of a new galaxy: ribbons of magenta and gold gas clouds twist around nascent stars, "
+            "while distant supernovae bloom like cosmic flowers in the far reaches of the void. Below, the abyss "
+            "reveals faint echoes of forgotten civilizations—ghostly silhouettes of submerged cities shimmering "
+            "in layers of atmospheric haze. Cinematic volumetric lighting cuts through the scene as twin moons—one "
+            "copper-hued, one opalescent—rise on opposite horizons, casting long, intersecting shadows across "
+            "moss-covered ruins and crystalline flora that refract light into prismatic halos. Hyper-detailed, "
+            "photorealistic rendering with the atmospheric depth of Roger Deakins' cinematography, the "
+            "architectural grandeur of Zaha Hadid, and the cosmic wonder of James Jean's illustrations. Shot on "
+            "a mythical 150mm lens with shallow depth of field, 8K resolution, Unreal Engine 5 realism, subsurface "
+            "scattering on organic elements, and ray-traced reflections dancing across every water droplet in the "
+            "starlight waterfalls. Ethereal, melancholic, and transcendent mood—like a moment of quiet revelation "
+            "at the edge of existence."
+        ),
         max_lpips=0.15,
         num_inference_steps=20,
     ),
@@ -391,12 +411,6 @@ _OUTPUT_DIR = Path(os.environ["VLLM_OMNI_QUALITY_OUTPUT_DIR"]) if "VLLM_OMNI_QUA
 
 def _quality_param(c: QualityTestConfig):
     marks = list(_marks)
-    if c.id == "fp8_z_image":
-        marks.append(
-            pytest.mark.skip(
-                reason="Z-Image FP8 quality gate temporarily disabled: https://github.com/vllm-project/vllm-omni/issues/3531"
-            )
-        )
     if c.id == "fp8_qwen_image":
         marks.append(
             pytest.mark.skip(reason="Qwen-Image FP8 quality gate temporarily disabled (see CI / issue tracker).")