What is the reason for not force-merging the actual PR when merge queue CI optimizations are on (closing them instead)? Once CI passes on the temporary merge queue PR, it seems like force pushing the real/original PR and then force-merging it would work? Is it just to avoid CI kicking off on the force-push? That could be solved at setup time by ignoring these pushes somehow.

Force-merging the original PR instead would mean rewriting the original PR branch to match that temporary PR, and GitHub does not always treat that flow cleanly or reliably as a normal merged PR. Closing the original PR is the safer and more consistent approach, while Graphite still treats it as merged in the product.

GitHub does not always treat that flow cleanly or reliably as a normal merged PR

ok, interesting… are those Github bugs or specific to the customer configuration?

Closing the original PR is the safer and more consistent approach, while Graphite still treats it as merged in the product.

Sure, but it breaks Github features (no link to the PR from the commit anymore [with linear history] – btw. this isn't mentioned in your docs IIRC) and as you know, Linear doesn't resolve the issue.

are those Github bugs or specific to the customer configuration?

believe this is due to github limitation/behavior. we do have an open ticket to address this and i've added your feedback to it.