Say in every declaration the assignment generation it came from, and record every send (hq issue 234)

A declaration newer in sequence than every other named four fewer modules
than the assignments held, a machine applied it, and nothing the mesh kept
said who sent it or from what view. The store now raises an assignment
generation in the same transaction as every assignment change (a trigger,
so a cascade counts too); a send reads it before composing, carries it to
engines that said they read it, marks a gate's put-back, and is recorded
with its sequence, sender, generation and modules. The would-send is
stamped with what was last sent, so nothing reads behind for it; a refusal
is kept on the send it refused and raised as S20 naming the sender; plan
says what the machine was last told.

cmd/mesh-controller/status_summary.go

@@ -196,6 +196,11 @@ func (l nudgingListener) Heard(ctx context.Context, report link.Report) (bool, e
 	if report.Ordered() {
 		link.StaleRefusals.Lifetime(report.Node, report.RefusedOlder, now)
 	}
+	// A send refused for the generation it was composed from is kept on the send it refused, so S20 names
+	// its sender (novox/hq issue 234).
+	if report.OlderGeneration != nil {
+		heardGenerationRefusal(ctx, l.Enrolment.Inventory, report)
+	}
 	// What the machine's witnesses put back and stand by (novox/hq ADR 0236): read by the gate and its
 	// probe. Only from an account of the machine — not a word that a declaration was set aside, nor a rekey.
 	if report.Superseded == "" && report.Rekey == nil && report.Node != "" {