If I've been quiet it was because I've been working at it solidly. Mrs Seal is delighted that she could read without interruption for several days. I've finished and back to the sandbank in time to watch Arsenal.
What a brilliant puzzle - one of the very best I've ever encountered. Many thanks Aedites. Thanks also to Loge (post 6), Turast (post 30) and, as ever, Malone (post 65 for confirming my understanding). This thread is so welcome in lock-down.
(Could someone parse the Detroit workers clue? where does remove frame of mirror come in?)