MultipartUploader: partSizeMB is actually bytes, and resume state is dead code

[yash-sangwan]

Three problems tangled together in this class.

The unit is wrong. The config field is called partSizeMB but it is compared against 5 * 1024 * 1024 and assigned straight to a byte count. UploadManager happens to pass bytes so it works, but BYOS3ApiProvider.uploadMultipartParallely forwards params.partSizeMB from the caller untouched. Anyone passing 10 meaning 10MB fails the >= 5242880 check and silently gets 5MB parts instead.

Resume can never work. The constructor calls localStorage.removeItem for this key, and saveState writes to that same key after every part. So a fresh uploader wipes the saved state before anything could read it. Nothing ever calls a restore path. The persistence is write-only.

It breaks outside the browser. That localStorage call sits in the constructor of a package whose tsconfig targets Node (module: NodeNext) and whose own test suite runs in environment: 'node'. Constructing a MultipartUploader server-side throws localStorage is not defined.

Where:

• s3-api/src/utils/multipartUploader.ts (lines 33-38, 40-51, 150-184)
• s3-api/src/core/types.ts (MultipartUploadParams, MultipartUploadConfig)
• s3-api/src/index.ts (uploadMultipartParallely)

What to do:

• Pick one unit and name it honestly - either partSizeBytes, or keep MB and multiply inside the constructor
• Guard localStorage behind a typeof window !== 'undefined' check, or inject a storage adapter
• Either finish resume-across-reload (look up saved state by key on construction instead of deleting it) or delete saveState entirely - right now it is pure overhead writing JSON to localStorage after every part