Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
The engine refused to start because the dictionary of effects was unreadable or inconsistent. Every builtin states what it may do to the heap, whether it reads, whether it writes, what it touches, in a short line of positional words. The position tells you the meaning: the first word answers one question, the second word answers another. The dictionary that explains all of this lives in effect.feml. This time the engine could not use it. Maybe the file was unreadable, maybe it declared no axes, maybe two positions collided, or maybe one axis allowed no words at all. And why does position matter so much? Imagine a form where the boxes shift by one: every row in builtins.feml would suddenly mean something else, without a single character of any row changing. That is a quiet, dangerous failure, so the engine checks the positions here, at birth. It will not fall back on a built-in default, because that would be a second source of truth. The message names the file and what went wrong. Fix effect.feml so every axis has a unique position and at least one word, and start again.
Text from the Rush engine's error catalogue.