Hold a joining build for a person without superseding its delivery, join only on an engine that keeps own groups, and keep a held module's settings (hq ADR 0328 §8, ADR 0334; re-review of 96e15f86)

A delivery does not send a joining build held for its library or its engine: the module waits for a person,
the plan stays open saying so and judges its other modules, and sends it once nothing holds it. A held move is
no move for the gate. A module joins only on an engine at contract 7, and a held module is composed with the
settings it last ran with. The runner's verdicts are said for their modules and judged by whether a move
changes them. mesh-host pinned at #97 (7a41e120), its bundle now examples/foundation-first-node.lock.

internal/link/protocol.go

@@ -457,6 +457,10 @@ const LibraryContract = 6
 // Identity and put that account in the group mesh-<module>, and accept a directory mode whose first digit is 2.
 const OwnGroupContract = 7
 
+// KindRunner is the tool runner's membership as the engine states it (novox/hq ADR 0334 §2; mesh-host internal/link):
+// `runner:<module>` of a joining module, in its own group; `runner:library:<name>` of no module, in a library's group.
+const KindRunner = "runner"
+
 // KindLibrary is a library's own verdict on its home, as the engine may state it (novox/hq ADR 0328): healthy once
 // kept. Read beside an access verdict naming the library until the engine's shape is settled.
 const KindLibrary = "library"