Custom search context to a model admin in silverstripe 4.7.3

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I need to add custom search context to a model admin in silverstripe 4.7.3. How can I do that?

I did this recently in 4.7.2 - I’m not sure the difference between the versions.

I had an extension applied to the Admin.

In the extension, an updateSearchContext() returned the form fields.

In the Admin, I had a getList() and a getFilterParams.

getList calls getFilterParams (as they can be set in a variety of ways) then uses those params to filter the list and returns it.

I can add some code if it’s still relevant 4.7.3.

I did also have this weird issue I couldn’t find a way to fix: Admin search forms don't respect setTemplate() calls