When a connection is lost, what happens after automatic reconnection, such as to a file that had downloaded partially?
Sorry, I do not understand what you mean by "such as to a file that had downloaded partially".
What if the file size is less than the transfer endurance threshold?
If you use the
switch, the transfer is resumed. But you should not use the switch in general, when doing mass upload. Because you may end up combining different versions of files.
What if the get command has -resume, -transfer=ascii, -resumesupport or -neweronly switches?
WinSCP never resumes files in ASCII/text mode.
Why is temporary file naming tied to whether the beginning of a file is re-downloaded?
Do not understand the question.
And why would you want temporary file naming only for binary files over a threshold size?
Binary files: It's not about binary files, but binary transfer mode. In text/ascii mode, particularly, when file conversion is done by the server, you cannot tell, what part of the file the server has. Because you only know a file size of a converted file, but that won't tell you, what was the size of an original file.
Threshold size: Because there's some overhead with checking existence of a partial file and renaming of the file. When transferring zillions of tiny files, you can tell the difference. It's configurable, so you can change it.