error: "key" to "max" has incompatible type

Bug Report

mypy fails to typecheck set(max(S, key=len)) in the below code. Splitting it into first computing X = max(S, key=len) and then computing set(X) passes the type checks. The problem persists when providing type annotations.

To Reproduce

S = [[1, 2], [3]]

X = max(S, key=len)
Y = set(X)
Z = set(max(S, key=len))

print(Y, Z)

L : list[list[int]] = [[1, 2], [3]]

A : list[int] = max(L, key=len)
B : set[int] = set(A)
C : set[int] = set(max(L, key=len))

print(B, C)

Running with Python 3.14.3 gives the correct output

{1, 2} {1, 2}
{1, 2} {1, 2}

Running with mypy 3.19.1 reports the following errors for the lines computing Z and C.

mypy_max.py:5: error: Argument "key" to "max" has incompatible type "Callable[[Sized], int]"; expected "Callable[[Iterable[int]], SupportsDunderLT[Any] | SupportsDunderGT[Any]]"  [arg-type]
mypy_max.py:13: error: Argument "key" to "max" has incompatible type "Callable[[Sized], int]"; expected "Callable[[Iterable[int]], SupportsDunderLT[Any] | SupportsDunderGT[Any]]"  [arg-type]
Found 2 errors in 1 file (checked 1 source file)

Start by running the supplied reproduction with mypy 3.19.1 and compare the failing inline calls with the accepted intermediate-variable form. Trace the type checking of max(..., key=len) and add a regression test covering both Z and C; done means the reproduction passes without the reported arg-type errors.