When navigating to a post path contextualized to a group the user doesn't have access to, but which is posted to a group they do have access to, they are currently shown an error page:
They should instead be redirected to viewing the post in a context in which they are allowed to see the post. If the post is public, redirect to the Public context, or to the first group the post is in which the user does have access to (OR just to the All Groups context default).
When navigating to a post path contextualized to a group the user doesn't have access to, but which is posted to a group they do have access to, they are currently shown an error page: They should instead be redirected to viewing the post in a context in which they are allowed to see the post. If the post is public, redirect to the Public context, or to the first group the post is in which the user does have access to (OR just to the All Groups context default).