Fix flash-attn build: install with --no-build-isolation so it can access torch

Dockerfile

@@ -30,12 +30,18 @@ RUN echo "⏱️  [BUILD] Installing ESPnet dependencies..." && \
     pip install --no-cache-dir -r /tmp/requirements-espnet.txt && \
     echo "✅ [BUILD] ESPnet dependencies installed"
 
-# Stage 3: Remaining dependencies including flash-attn
-# IMPORTANT: torch is already installed from base, so flash-attn can build
+# Stage 3: Remaining dependencies (excluding flash-attn)
 COPY requirements.txt /tmp/requirements.txt
-RUN echo "⏱️  [BUILD] Installing remaining dependencies (Flash Attention compilation may take 5-15 minutes)..." && \
+RUN echo "⏱️  [BUILD] Installing remaining dependencies..." && \
     pip install --no-cache-dir -r /tmp/requirements.txt && \
-    echo "✅ [BUILD] All Python packages installed"
+    echo "✅ [BUILD] Remaining dependencies installed"
+
+# Stage 4: Install flash-attn separately with --no-build-isolation
+# flash-attn needs torch to be available during build, but pip's build isolation
+# prevents it from seeing installed packages. --no-build-isolation fixes this.
+RUN echo "⏱️  [BUILD] Installing Flash Attention (compilation may take 5-15 minutes)..." && \
+    pip install --no-cache-dir --no-build-isolation flash-attn>=2.3.0 && \
+    echo "✅ [BUILD] Flash Attention installed"
 
 # Set up app directory
 WORKDIR /app

requirements.txt

@@ -1,13 +1,9 @@
 # Remaining dependencies not in requirements-base.txt or requirements-espnet.txt
 # These are installed after base and ESPnet for optimal caching
-# NOTE: torch is installed from requirements-base.txt, so flash-attn can build successfully
+# NOTE: flash-attn is installed separately in Dockerfile with --no-build-isolation
 jiwer>=3.0.0
 
 # Build dependencies for Flash Attention compilation
+# (flash-attn itself is installed separately in Dockerfile)
 packaging>=21.0
 ninja>=1.10.0
-
-# Flash Attention - optimized for NVIDIA A10G GPUs (Ampere architecture)
-# Required for best performance on HF Spaces with GPU
-# NOTE: torch must be installed first (from requirements-base.txt) for flash-attn to build
-flash-attn>=2.3.0