Make plans backwards compatible (#37941)

This PR fixes the backwards compatibility of the new `Plan` variants.

We can't add new variants to the wire representation, as old clients
won't be able to understand them.

Release Notes:

- N/A
cb75c2aeb7Marshall Bowers committed on 9/10/2025, 8:11:07 PM· committed by GitHubparent2c29eac
18 files changedLine totals unavailable