- Add DELETE endpoints for tags, packages, and projects with proper ref_count
decrements for all affected artifacts
- Implement atomic ref_count operations using SELECT FOR UPDATE row-level locking
to prevent race conditions
- Add custom storage exceptions (HashComputationError, S3ExistenceCheckError,
S3UploadError) with retry logic for S3 existence checks
- Handle race conditions in upload by locking artifact row before modification
- Add comprehensive logging for all ref_count changes and deduplication events
- Include ref_count in upload response schema
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