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 file describing the seam between its two heaps was unusable. A seam is where two things meet. Here, a verb in the ExecHeap needs to work with a container that lives in the DataHeap. The rule is that it reaches the container by reference, a coordinate pointing into the DataHeap, and never by copying or inlining it. That means the reducer only ever deals with two things: plain scalars, and references. If a reducer had to switch over every possible value type, that would be a symptom of a heap that was never properly split. The details of the seam, how many arms a payload slot has, that there is no container arm, what the reducer switches on, live in run.feml. This time, the engine could not read it, or it said none of those things. Without it, there is nothing to measure the seam against. The engine will not fall back on a hidden default, so it stops. Check the path in the message, fix the file, and start again.
Text from the Rush engine's error catalogue.