Granting on Subscription-managed Entitlements

[GAlexIHU]

I realize this is an old PR but I'm curious why this is not an intended use case for OpenMeter to support? It seems this is a very natural way to support subscriptions + overage.

I don't believe this can be accomplished by editing the subscription as the subscription is just a standard base and overage should be something extra that's variable-charged on top of that.

I also tried to do this with add-ons but it doesn't work because the add-ons renew on the same basis as the underlying subscription, but overages should be one-off additions to the entitlement and not renew.

It seems this is exactly what grants were designed for, but I can't figure out why grants cannot be applied to entitlements managed by subscriptions. With this restriction in place, it seems the only way to get the desired behavior is to basically reimplement subscriptions using raw entitlements and apply grants onto those.

Is there some other suggested way to manage this with OpenMeter? cc @GAlexIHU

Originally posted by @christopherhwood in https://github.com/openmeterio/openmeter/issues/2481#issuecomment-3226424350