What broke
A session clone that could clone but not push carried a commit for a whole evening. The files it held were delivered by another route and published under a commit the clone never saw. The next session found the clone’s commit, took it for the versioned truth, and was about to rebuild the published work on a base that no longer existed anywhere but there.
The rule it paid for
Durable means reachable from a pushed ref, for a seat’s own workshop too. A clone that cannot push keeps no commit and no modified file between two turns: it transforms, delivers, and is reset to the published head. What was prepared lives in the delivered files and in the replayable script, never in the clone.