The draft Spec PR and its Tickets checklist

Parent

The Spec PR exists from the first landed Ticket onward, as a draft that shows the Spec's progress.

Opening. As soon as the first Ticket lands on the Spec branch (GitHub won't open a PR with no commits), thirdshift opens the Spec PR as a draft, from the Spec branch into the Base branch, titled from the Spec, with Closes #<spec> and a Tickets checklist in its body.
The Tickets checklist. Written by thirdshift between fixed markers, so it can be replaced without touching the prose around it. One line per Ticket with its state: done (ticked, with its PR), running, failed, blocked, unready. Updated each time a Ticket lands or fails.
After the Spec review. The Spec review rewrites the body through /pr; thirdshift then puts the Tickets checklist back (replacing it between the markers, or appending it if the markers are gone) before marking the PR ready.
A Failed spec run leaves the Spec PR as a draft, its checklist showing what's missing, and prints its URL on stdout.

The Spec PR does not exist before the first Ticket lands, and exists as a draft right after, with Closes #<spec> and the checklist
Each Ticket that lands is ticked in the checklist, with its PR
A Ticket that fails, or is unready or blocked, is shown as such in the checklist
Text outside the markers is left as it was when the checklist is updated
After the Spec review rewrites the body, the checklist is present in the ready Spec PR
A Failed spec run leaves the Spec PR a draft and prints its URL on stdout, with exit 1