high95%
core: _convert_openai_format_to_data_block hard-codes mime_type on base64 file blocks
In langchain-core's OpenAI message translation, base64-encoded file blocks always get mime_type='application/pdf', ignoring the MIME type specified in the data URI. This causes non-PDF files (e.g., CSV, text) to be silently mislabeled, which can break downstream processing that relies on content_blocks.