We provide this diagnostic in ty (https://docs.astral.sh/ty/reference/rules/#possibly-unresolv...), but it's disabled by default because it can have false positives in many scenarios where the code works at runtime (this is true also in the type checkers that enable it by default). A typical example is code like

  def _(flag: bool):
    if flag:
      x = True
    ...
    if flag:
      read(x)

But it's easy to turn the rule on if you want it:

  [tool.ty.rules]
  possibly-unresolved-reference = "error"