heapx is a single-file C extension for Python that implements heap operations with explicit, performance-driven design choices at every level of the implementation. The module provides six public API functions — heapify, push, pop, remove, replace, and merge — each backed by a multi-tier dispatch system that selects the optimal algorithm at runtime based on data structure type, heap size, arity, key function presence, element type homogeneity, and GIL-release eligibility.