String Template Substitution with Nested Variable Replacement and Cycle Detection

Implement a string substitution system that replaces placeholders (formatted as %var% or similar) in a text string with corresponding values from a given mapping. The solution must handle nested substitutions, where replacement values may themselves contain additional placeholders that require further resolution. Use recursive or iterative approaches to fully resolve all substitutions. Additionally, detect and handle cyclic dependencies between replacement keys — if a cycle is detected, return an appropriate error or indication.