Detailed Description

Streaming file upload to an Arduino FS (PC_ENABLE_UPLOAD).

Registers a POST route whose request body is streamed straight into a file on a filesystem (LittleFS / SPIFFS / SD) in FILE_CHUNK_SIZE pieces - the upload never has to fit in RAM. Reuses the parser's streaming-body hook (the same mechanism OTA uses), so it is zero-heap and bounded.

One upload at a time (the device runs a single loop task). Only one streaming sink can be installed, so PC_ENABLE_UPLOAD and PC_ENABLE_OTA share the parser hook - register whichever you need (not both on the same build).

Definition in file upload_service.h.