Both sides bootstrapped CONCEPTS.md — kept main's broader structure (Missions,
Merge lifecycle, CE sessions) and folded the branch-group vocabulary into its
Merge-lifecycle cluster (enriched Shared branch group + Self-healing sweep;
added Branch assignment mode, Landed, Group promotion). Union-merged core
index/store imports; took main's AGENTS.md discoverability wording. Also adds
execFile to the two child_process test mocks that only stubbed exec (the
coordinator's argv-based git calls now require it).
