A group-owned trigger marked `shared = true` watches a §11.6 shared
collection instead of per-app collections — the namespace boundary that lets
a shared-collection write fire a trigger. Mirrors the sealed column; existing
rows default false (per-app, unchanged). Match-query split + emission land in
M2.2/M2.3.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
