# X_NOT_IMPLEMENTED_COPY

## Means

a package other than `@ultimat3/core` constructs `X_NOT_IMPLEMENTED` itself

## Typical cause

core ships the one class (`NotImplementedError`); ten packages each grew a `(feature, fix)` wrapper of their own, with ten cause sentences for one fault, until plan 101 deleted them. A `code:` key, a `static readonly code =` and a `code:` held in a module const are all one finding; a registry's `*_BORROWED_ERROR_CODES` list names the code and raises nothing. A class that must be caught by identity extends core's (`DevSourceUnavailableError`)

## Fix

`bun run scripts/not-implemented-copies.ts --json`, then in the named file throw `new NotImplementedError({ cause, fix })` from `@ultimat3/core` — a `fix:` written at the call site is one the errors step reads

[CLI and verify](/error-codes#cli-and-verify)