A lambda with no type parameters of its own, contextually typed by a
generic signature (`send: (m) => …` for an interface's `send<T>(m:
Message<T>): string`), takes that signature's type parameters: its
parameter is `Message<T>`. A generic lambda written with its own type
parameters already lowers once, erased, with them bound to `unknown`, but
this one tried to map `Message<T>` with `T` unbound and was refused
(SC2009).
It now lowers the same way, erased, binding the contextual signature's
type parameters to `unknown`. Parameters bound in the enclosing scope
keep their bindings.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
