Turning the merge check on for every repository showed it asked the wrong questions: a
repository chose whether it was checked, the gate mapped a change onto modules its own
way, the shared-code rule rebuilt 103 modules for a root script, and nothing kept a
commit off the trunk from becoming a module's version. Records the operator's decisions,
narrows ADR 0237 decision 4, revises to-be 45 §9 and Phase 5 and to-be 30, closes issue
280's left-open, and gives this repository its own merge-check.sh.
