Rewrite session state as the pre-publish handoff for v3.0.0

Everything in 3.0.0 scope is on main. What remains is #50 (a repo-settings
action only Elliot can take), then the tag, then publish. Records the eight
final checks to run in order before tagging, the disposition of every open
issue, the standing safety rules for live testing, and recovery SHAs for the
branches and stash removed during cleanup.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: ElliotDrel