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When a workflow input is a file, the SDK uploads it as multipart/form-data (the same shape as curl -F). No base64, no payload doubling.

From a Path

Filename and MIME type are inferred automatically.

From a file handle

Filename inferred from f.name.

From raw bytes

Multiple files

Each file becomes a files.<fieldName> multipart part. Mix files and scalar inputs freely; scalars ride in the input JSON part automatically.

Nested files are not extracted

Only top-level file values become multipart fields. Files inside lists or nested dicts stay in the input JSON part and the server will not see them as uploads:

Do not base64 yourself

The SDK picks multipart whenever it sees a Path, file-like object, or {"content": ..., "filename": ..., "mime_type": ...} dict. Plain strings pass through as scalar inputs.