git-webkit upload should amend the commit instead of trying to create a new commit in each invocation. Looks like this option exists but not enabled by default? --amend.
There isn't consensus on the right behavior yet - some people prefer additional changes to be separate commits to make reviewing easier. And then squash before landing.
(In reply to Alexey Proskuryakov from comment #1) > There isn't consensus on the right behavior yet - some people prefer > additional changes to be separate commits to make reviewing easier. And then > squash before landing. Maybe this should be configurable during setup?
<rdar://problem/96837043>
So... apparently merge-queue can't land a PR unless all commits are squashed so the current behavior of git-webkit upload is incompatible with merge queue.