explanations about model persistency in containers

Dockerfile

@@ -24,11 +24,11 @@ RUN apt-get update && \
 RUN python3 -m venv /opt/venv
 ENV PATH="/opt/venv/bin:$PATH"
 
-# upgrade pip + setuptools + wheel and increase timeout/retries for large torch wheels
+# timeout/retries for large torch wheels
 RUN pip3 install --upgrade pip setuptools wheel && \
     pip3 --disable-pip-version-check install --timeout=120 --retries=5 \
         --index-url https://download.pytorch.org/whl/cu129 \
-        torch torchvision torchaudio \
+        torch torchaudio \
     || (echo "Initial install failed — retrying with extended timeout..." && \
         pip3 --disable-pip-version-check install --timeout=300 --retries=3 \
             --index-url https://download.pytorch.org/whl/cu129 \
@@ -45,8 +45,20 @@ RUN if [ -n "$EXTRAS" ]; then \
       pip install --no-cache-dir whisperlivekit; \
     fi
 
+# In-container caching for Hugging Face models by: 
+# A) Make the cache directory persistent via an anonymous volume.
+#    Note: This only persists for a single, named container. This is 
+#          only for convenience at de/test stage. 
+#          For prod, it is better to use a named volume via host mount/k8s.
 VOLUME ["/root/.cache/huggingface/hub"]
 
+
+# or
+# B) Conditionally copy a local pre-cache from the build context to the 
+#    container's cache via the HF_PRECACHE_DIR build-arg.
+#    WARNING: This will copy ALL files in the pre-cache location.
+
+# Conditionally copy a cache directory if provided
 RUN if [ -n "$HF_PRECACHE_DIR" ]; then \
       echo "Copying Hugging Face cache from $HF_PRECACHE_DIR"; \
       mkdir -p /root/.cache/huggingface/hub && \
@@ -55,6 +67,7 @@ RUN if [ -n "$HF_PRECACHE_DIR" ]; then \
       echo "No local Hugging Face cache specified, skipping copy"; \
     fi
 
+# Conditionally copy a Hugging Face token if provided. Useful for Diart backend (pyannote audio models)
 RUN if [ -n "$HF_TKN_FILE" ]; then \
       echo "Copying Hugging Face token from $HF_TKN_FILE"; \
       mkdir -p /root/.cache/huggingface && \