Load Actions… read the whole file before checking the 8 MiB limit, so
picking a very large file could take a lot of memory before it was
refused. A new read_head service reads at most a given number of bytes;
the desktop app provides it, and loading an action set reads one byte
past 8 MiB with it. A larger file is refused without reading the rest.
Hosts without the service keep reading the whole file. Automation
roots apply to read_head as they do to read.