"Do some applications running on Unix-likes —if not the system's API— treat //foo/bar Paths specially?"

I am aware of Perforce which uses //depot/A/B/C/D Paths to refer to the Depot. Perforce also supports //Client/C/D Paths, when the Client is pointing to //depot/A/B/. Here, local FileSystem may not have these Paths.

"p4 filelog //depot/A/B/C/D" will show the history of that file, even though there is no file /depot/A/B/C/D.

"p4 filelog C/D" will also show the history of that file, if executed from appropriate Directory.

Reference : https://www.perforce.com/perforce/r12.1/manuals/cmdref/o.fspecs.html

Do some applications running on Unix-likes —if not the system's API— treat //foo/bar Paths specially?

I am aware of Perforce which uses //depot/A/B/C/D Paths to refer to the Depot. Perforce also supports //Client/C/D Paths, when the Client is pointing to //depot/A/B/. Here, local FileSystem may not have these Paths.

p4 filelog //depot/A/B/C/D will show the history of that file, even though there is no file /depot/A/B/C/D.

p4 filelog C/D will also show the history of that file, if executed from appropriate Directory.

Reference : https://www.perforce.com/perforce/r12.1/manuals/cmdref/o.fspecs.html