Redefinition without reassignment doesn't check existing value

With --allow-redefinition, mypy allows a variable to be redefined, without checking that the existing value is the correct type.

a: str = "foo"
print(a)  # value needs to be used before redefinition
a: int  # but it is really still str
if a > 1:
    ...

https://mypy-play.net/?mypy=latest&python=3.10&flags=allow-redefinition&gist=79d1e9219d66da441050ba730a7c2842

Expected Behaviour

In this example, mypy should detect that a is still a str, and not allow this redefinition.

It could treat the redefinition as though it is a new variable, being assigned the value of the existing one. That would result in an error like:
error: Incompatible types in assignment (expression has type "str", variable has type "int")

Or it could be a new error, like:
error: Redefinition incompatible with existing type (existing type "str", new type "int")

Actual Behaviour

mypy:

Success: no issues found in 1 source file

python:

TypeError: '>' not supported between instances of 'str' and 'int'

Beginne damit, das Beispiel aus dem verlinkten mypy-play.net-Lauf mit --allow-redefinition zu reproduzieren, und verfolge dann, wie mypy annotierte Neudefinitionen verarbeitet. Die Arbeit ist abgeschlossen, wenn der vorhandene str-Wert anhand der späteren int-Annotation geprüft wird und mypy statt eines Erfolgs einen entsprechenden Fehler meldet.