Thank you for the PR @theseion! Two things to note still:

• there will most likely not be a squeak5.4, only squeak6
• I have a hunch that squeak<=5.3 builds would also break if their cached images were ever updated to include the newer Metacello. A more longterm fix for this odd dependency incompatibility issue might thus be actually a check whether STON is already in the image instead of dispatching based on version.

But I'm not a 100% sure on the second point just yet. Is this issue in any way time-critical for you? Otherwise I would check laeter today or tomorrow (unless you beat me to it of course :)) and report back, if successful maybe with a new PR based on yours.

SmalltalkCI overrides STON-Core in Squeak trunk

True. But 6 has been coming for about 2 years now? And 5.4 matches the Metacello attribute if I'm not mistaken. For safety, we could add #squeak6.x to the spec for 5.4.

I have a hunch that squeak<=5.3 builds would also break

Right. I wasn't aware that's an option.
We could just put that check into the baseline, like you suggested. I think that would be fine. There is one alternative though and that is to depend on a specific Metacello version in the SmalltalkCI baseline. I don't think we should do that but I'm pointing it out for completeness.

This isn't time critical but would be nice to get fixed in the next couple of days (or weeks). Feel free to adapt the PR.

Superseded by #530.