ADR 0270: the forge's ancestry decides covered, and say what covered means and does not (review of #241)

Merge order on a protected trunk is kept only as the first filter; the forge's compare, through a new
read-only tool, decides whether a later merge contains a held one. A merge held without a passing check is
covered only by a later delivery whose own check passed. Covered says a later merge that contains it was
delivered, not that the change runs: a revert in between stays possible. A delivery that only adds a module
is delivered whatever its build does, and covered wins over go when a person's walk fails between two
readings. The glossary gains covered beside superseded and delivered.

ADR 0271 names the bus upgrade as the mesh call and says S17 clears once the step sent the new bus.

00-META/glossary.md

@@ -319,6 +319,11 @@ planner, the walk). **Downstream of** Module, Core, Health and repair and Data.
   `held`, and the final four). Not *change* (a diff). *Pipeline* is the predecessor's build-and-deploy
   mechanism, which the as-is designs describe; it is never a word for a delivery.
   *Not:* ~~deployment~~ (hq)
+- **covered** — the end of a delivery that a later merge containing it delivered: every module it moves was
+  sent to every machine running it by the walk of a later merge into the same trunk, delivered on its own
+  passing check, whose merge commit the forge says contains this one. Not *superseded*, which is a delivery
+  whose walk a newer delivery took over before it ended; nor *delivered*, which its own walk or an empty plan
+  ends in ([ADR 0270](../02-DECISIONS/0270-a-held-delivery-that-moves-nothing-or-that-a-later-delivered-merge-contains-ends-by-itself-and-a-hold-whose-reason-is-gone-lifts.md), proposed).
 - **delivery group** — two or more deliveries sharing a pull request head branch name across the mesh's
   repositories, delivered as one unit in an order declared (`after:`) or inferred by the planner. One
   level: a group holds deliveries, never groups. Its state is derived from its members, never set.