Add diffusers backend support for image generation

Dockerfile

@@ -147,6 +147,44 @@ RUN curl -LsSf https://astral.sh/uv/install.sh | sh \
     && ~/.local/bin/uv pip install --python /opt/sglang-env/bin/python "sglang==${SGLANG_VERSION}"
 
 RUN /opt/sglang-env/bin/python -c "import sglang; print(sglang.__version__)" > /opt/sglang-env/version
+
+# --- Diffusers variant ---
+FROM llamacpp AS diffusers
+
+ARG DIFFUSERS_VERSION=0.31.0
+ARG TORCH_VERSION=2.5.1
+
+USER root
+
+RUN apt update && apt install -y \
+    python3 python3-venv python3-dev \
+    curl ca-certificates build-essential \
+    && rm -rf /var/lib/apt/lists/*
+
+RUN mkdir -p /opt/diffusers-env && chown -R modelrunner:modelrunner /opt/diffusers-env
+
+USER modelrunner
+
+# Install uv and diffusers as modelrunner user
+RUN curl -LsSf https://astral.sh/uv/install.sh | sh \
+    && ~/.local/bin/uv venv --python /usr/bin/python3 /opt/diffusers-env \
+    && ~/.local/bin/uv pip install --python /opt/diffusers-env/bin/python \
+        "diffusers==${DIFFUSERS_VERSION}" \
+        "torch==${TORCH_VERSION}" \
+        "transformers" \
+        "accelerate" \
+        "safetensors" \
+        "fastapi" \
+        "uvicorn[standard]" \
+        "pillow"
+
+# Determine the Python site-packages directory dynamically and copy the Python server code
+RUN PYTHON_SITE_PACKAGES=$(/opt/diffusers-env/bin/python -c "import site; print(site.getsitepackages()[0])") && \
+    mkdir -p "$(dirname "$PYTHON_SITE_PACKAGES")" && \
+    cp -r python/diffusers_server "$PYTHON_SITE_PACKAGES/"
+
+RUN /opt/diffusers-env/bin/python -c "import diffusers; print(diffusers.__version__)" > /opt/diffusers-env/version
+
 FROM llamacpp AS final-llamacpp
 # Copy the built binary from builder
 COPY --from=builder /app/model-runner /app/model-runner
@@ -158,3 +196,7 @@ COPY --from=builder /app/model-runner /app/model-runner
 FROM sglang AS final-sglang
 # Copy the built binary from builder-sglang (without vLLM)
 COPY --from=builder-sglang /app/model-runner /app/model-runner
+
+FROM diffusers AS final-diffusers
+# Copy the built binary from builder
+COPY --from=builder /app/model-runner /app/model-runner

backends_vllm_stub.go

@@ -9,7 +9,7 @@ import (
 )
 
 func initVLLMBackend(log *logrus.Logger, modelManager *models.Manager) (inference.Backend, error) {
-	return nil, nil
+	return nil, nil // VLLM backend is disabled
 }
 
 func registerVLLMBackend(backends map[string]inference.Backend, backend inference.Backend) {