am deploying a FastAPI backend to Railway connected to a Railway Postgres database.

The deployment consistently fails during the build phase at:

pip install -r requirements.txt

Build logs show:

ERROR: Could not find a version that satisfies the requirement fast==0.110.0
ERROR: No matching distribution found for fast==0.110.0
ERROR: failed to build: process "pip install -r requirements.txt" exited with code 1

The application is a Python FastAPI API using:

- FastAPI
- Uvicorn
- SQLAlchemy
- Railway Postgres (connected successfully)
- GitHub auto-deploy

The Postgres service is online and DATABASE_URL is correctly injected into the backend service environment variables.

The issue appears related to dependency resolution during Railway’s build process. A non-existent package version ("fast==0.110.0") was previously referenced, which prevented pip from completing installation.

Actions already taken:
- Updated requirements.txt to use valid FastAPI dependency
- Verified Python runtime installation
- Confirmed start command:
uvicorn app.main:app --host 0.0.0.0 --port $PORT
- Redeployed after committing fixes

Request:
Please confirm whether Railway build caching or dependency resolution could still be referencing an older requirements layer, and advise if a clean rebuild or cache purge is required.

Repository deploys correctly locally but fails only during Railway build.