Snapcraft 8, recently released to stable (as mentioned in Call for testing: Snapcraft 8.0.0) allows targeting core24 properly. The syntax today requires the following construct:
This forces the resulting snap to have a grade of devel. In essence this means that a snap build with the devel build-base cannot be released to stable or candidate channels. The reason for this is simple, this snap cannot be guaranteed to work on the yet to be stable core24 base. Additionally, there are changes in Snapcraft itself that can take place until this time, so far no changes are anticipated, but there might be some due to integration issues with core24.
There is a timeline in place, that aligns with that of Ubuntu defined at Noble Numbat Release Schedule - Release - Ubuntu Community Hub. At most at feature freeze, currently defined there to be 2024-02-29T03:00:00Z Snapcraft will have a release on the beta channel which would no longer require the
build-base key to be defined. Making it so, so that snaps built with that version of Snapcraft to be of grade stable.
On the day of Beta Freeze of Ubuntu, marked to be 2024-04-01T00:00:00Z the version of Snapcraft on the beta channel will migrate to the candidate channel.
On Ubuntu release day, the Snapcraft version in the candidate channel would have made it to stable.