How to keep SwiftData from crashing your app on ModelActor release and staged migrations

If you adopted SwiftData expecting a friendlier Core Data, you have probably already met one of its lifecycle traps: a @ModelActor instance going out of scope and taking your fetched models with it, a routine 0.9 → 1.0 staged migration failing with Cannot use staged migration with an unknown model version, or a CloudKit-synced store…