Includes a regression test for the "no-op bend" case that reproduces
the user-reported 'fence bend cancels fence creation' bug: when
action.commit returns false (draft === original), no pastState push
happens during the drag's commit path. The very next Ctrl-Z falls
through to whatever was on the stack before activation — typically
the fence creation itself.
The actual dance with real changes (delta !=0) works correctly — the
test exercising the full createDragSession flow with action.commit
returning true pins one undo step covering only the drag.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
