Force-downgrade torchao to 0.6.1 after unsloth to fix register_constant crash

Dockerfile

@@ -9,10 +9,19 @@ ENV PATH="/home/user/.local/bin:$PATH"
 
 WORKDIR /app
 
-# Upgrade pip and install unsloth properly
+# Upgrade pip
 RUN pip install --no-cache-dir --upgrade pip
+
+# Install unsloth from GitHub (it will drag in a bleeding-edge torchao)
 RUN pip install "unsloth[colab-new] @ git+https://github.com/unslothai/unsloth.git"
-RUN pip install --no-cache-dir trl
+
+# CRITICAL: Force-downgrade torchao to last known-good version AFTER unsloth
+# torchao>=0.7 requires torch.utils._pytree.register_constant which does not
+# exist in any stable PyTorch release yet.
+RUN pip install --no-cache-dir --force-reinstall "torchao==0.6.1"
+
+# Pin trl and transformers to stable versions
+RUN pip install --no-cache-dir "trl>=0.15,<0.17" "transformers>=4.47,<4.51"
 
 COPY --chown=user ./requirements.txt requirements.txt
 RUN pip install --no-cache-dir --upgrade -r requirements.txt