# `Mutare.UseExpansion.ContractError`
[🔗](https://github.com/foxbenjaminfox/mutare/blob/v0.2.1/lib/mutare/use_expansion/contract_error.ex#L1)

Raised when an enabled `Mutare.UseExpansion` handler returns an invalid result or fails.

This is a configuration error in an installed extension, not a property of the target source. The distinct exception lets the otherwise failure-tolerant `use` harvesting boundary re-raise extension failures while still degrading safely when the target's own `__using__` cannot expand.

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*Consult [api-reference.md](api-reference.md) for complete listing*