Fix HF cache permissions and add startup fallback

[enveryasar]

Summary by CodeRabbit

• Chores
  • Improved Hugging Face model cache initialization with automatic directory setup during startup
  • Added graceful fallback handling if cache directory creation fails
  • Updated container environment configuration for cache directory paths

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 5b08a9e3-0ea5-4c25-a5a1-35053e64381b

📥 Commits

Reviewing files that changed from the base of the PR and between b35b909 and 59a1ed7.

📒 Files selected for processing (2)

• backend/app.py
• docker-compose.yml

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📝 Walkthrough

Walkthrough

Backend startup now sets a Hugging Face hub cache fallback directory under the app's configured cache path when HF_HUB_CACHE is not already set, creating it with graceful error handling. Docker Compose configuration is updated to expose this environment variable and removes the corresponding named volume.

Changes

Hugging Face Hub Cache Setup

Layer / File(s)	Summary
Backend HF cache environment and directory setup backend/app.py	Startup computes and sets HF_HUB_CACHE fallback directory under the app's configured cache directory, then creates the directory with graceful error handling that logs a warning without aborting startup if directory creation fails.
Docker Compose HF cache environment configuration docker-compose.yml	Environment variable HF_HUB_CACHE is set in the voicebox service to point to the cache directory under /app/data, and the previously used huggingface-cache named volume is removed from the compose volumes definition.

Estimated Code Review Effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A cache directory now has its home,
No volumes needed, just paths to roam,
Environment variables light the way,
Hugging Face models can stay and play!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main changes: fixing HF cache permissions and adding a startup fallback directory creation mechanism in both backend/app.py and docker-compose.yml.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[Xarianne]

I hit the same issue and suggested a fix in PR #584 — chown the data and cache directories in the entrypoint before the gosu privilege drop.

The issue with this PR's approach is that moving the cache to /app/data doesn't actually fix the root-ownership problem — /app/data is a named volume that's also mounted as root:root on first use, which is the same thing causing the SQLite attempt to write a readonly database error. The fallback in app.py would hit the same permission denied when trying to create /app/data/cache/huggingface/hub.

Fixing the ownership in the entrypoint before the privilege drop would resolve both the cache permission issue and the SQLite readonly error without needing the application-level fallback or moving the cache location.