Essay derivation — 213-native concept exposition

A 213 question (limit / completeness / equality / residue / gauge / ...) deserves more than a wiki paragraph or a Lean module pointer. It deserves an essay that simultaneously interprets the classical concept (packaging stripped per G6 §0) and refines the 213 narrative (operational primitive made syntactic).

This is the format theory/ book content takes on top of the 89-chapter catalog index. Catalog = static AST + reference. Essay = on-demand trajectory through catalog nodes for a specific query Lens.

When to invoke