I was trying to understand how to do this, and I formed the opinion that most of the battery providers don’t really allow the degree of ‘on/off’ or ‘charge/discharge’ customisation as might be necessary to make this work? Or was I fooled by the packaged products that are aiming to turn me and my battery and panels into a residential power plant at the whim of the energy company?

The most popular batteries provide all the customization you need and more. Soo many features... it is exhausting. Even 'AI' modes trying to predict usage and solar generation using weather forecasts and top up from the grid at cheap rates if it thinks the power will probably be needed. A battery like Sigenergy's you can setup on a time based charging schedule (most popular for the free power plans), or have it pull Amber's live wholesale rates and put it into AI mode to avoid using their SmartShift VPP, or just hand over the keys to a VPP provider and let them drive.

Ours is a FoxES or something and the included app is pretty straight forward. You can easily set it to ALWAYS pull from the grid during specific times and it will (along with the solar), charge the battery to capacity during that time.

You can set your own timing schedule and choose self-consumption or to sell back to the grid. Joining a VPP is optional.