Cycle marker — emitted instead of recursing when explain re-enters
a node already on the traversal stack. The engine's structural
registration guard rejects cycles, so this is a defensive frame
that keeps the walker total under any future relaxation.
Cycle marker — emitted instead of recursing when explain re-enters a node already on the traversal stack. The engine's structural registration guard rejects cycles, so this is a defensive frame that keeps the walker total under any future relaxation.