Build was failing, likely due to:
1. 165MB build context (no .dockerignore) — cccl_upstream/ 53MB, zip 97MB
2. probe_corex_api.py used importlib.import_module which may init CUDA
3. pip install without --timeout could hang on unreachable mirror
Fixes:
- .dockerignore: excludes cccl_upstream/, vllm/, *.zip, docs/ etc
Build context: ~2MB instead of 165MB
- probe_corex_api.py: rewritten to use ONLY ast.parse, zero runtime imports
- pip install: added --timeout 30
