Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
Your manifest says where the leafs live, but rush looked at that place and found something else. Here is the story. You wrote a leafs line in your manifest, pointing at a folder. Before saving a single byte, rush asks the operating system what is really mounted at that folder, and it expects to hear: a leafs filesystem. What if the folder is just an ordinary directory? Or the leafs store exists but nobody mounted it? Then a leaf path would quietly turn into a plain operating system path, and your data would land on ext4 or something similar without anyone choosing that. Rush treats that as a broken promise, so it stops and names the holder. The second slot of the message tells you what the folder really rests on, and how to mount leafs there. Think of a mailbox painted with your name that is actually a flower pot. The mail would pile up in the wrong place. The fix is simple: mount the leafs store at the declared folder, or correct the manifest so it points at the real mount. Then run again, and your holder rests where you meant it to.
Text from the Rush engine's error catalogue.