Let SessionMiddleware handle session saving about nav HOT 4 OPEN

An actual difference between calling save early and not: flush sets the session ID to None. calling save will generate a session ID. So removing the current extra save calls will make it so the session does not have a session ID until it reaches the SessionMiddleware's process_response function where save should be called

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And it seems, depending on what subclass of SessionBase that is being used. save calls cycle_key, meaning it will get a new session ID every time save is called.

The one we use, SessionStore, only generates a new key on save if it doesnt already have one. So extra save calls should be safe in our instance

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branch: save-in-middleware in my fork is a WIP attempt at this

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big problem i had: get session middleware to run properly during testing

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