Bootstrap exact-PR artifact publishers with an inert sentinel

Observed 2026-09-08 in e3-solutions/theft COR-4082 / PR #806: a one-shot GitHub Actions publisher that fail-closes on the exact PR number cannot know a newly created PR's number in its first commit. A safe narrow bootstrap is to commit an inert impossible PR-number sentinel with the release label absent, open the draft PR to obtain its real number, then replace both numeric guards with that number, freeze/review the final head, and only afterward apply the one-shot maintainer label. This preserves exact-head provenance without predicting repository sequence numbers or broadening the workflow trigger. Source provenance: repository workflow, GitHub PR metadata, and final diff inspection.