Explicit input instantiation escape hatch

**Is your feature request related to a problem? Please describe.**

I'm designing a stable external API that needs to wrap our existing fast-moving internal API. Sometimes, I want to call existing resolvers to do that.

However, when using deeply nested inputs with a `@property`, it's not possible to wrap that input with another (simplified) input, because I can't create an "instance" with the correct parameters on creation.

**Describe the solution you'd like**
I would like an escape hatch to instantiate inputs.

**Describe alternatives you've considered**
An inheritance-based mechanism where I could remove fields and structures from a parent might solve the problem, but I don't think it would be as clean.

No files, tests, or entry points are named. Clarify the intended input-instantiation API, especially how deeply nested inputs and @property fields should behave, then identify the existing input construction and resolver paths to inspect. Done should include a defined escape hatch and coverage for the wrapping use case.

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