Keep what each machine says of what it runs, raise it, and gate on it (hq ADR 0240, to-be 48 Phase A)

The gate judged a module by what the mesh saw from outside, so a container that
crash-looped after it applied passed it. Each machine's node-engine now states
the health of every long-running resource it runs; the controller keeps the
newest statement per machine, raises module.<module>.<machine>.unhealthy on the
second statement in a row, clears it on the first that does not say it, and the
gate passes a module only when every long-running resource of it is stated
healthy since the send. An engine that states nothing is judged as before.

internal/link/contracts.go

@@ -35,6 +35,10 @@ var Contracts = map[string]Contract{
 	KindHeartbeat: {Unordered: "a word that the machine is there: the newest heard is the newest said, and one " +
 		"lost is the next one"},
 	KindToolsHeartbeat: {Unordered: "a word that the node tools are there, as a machine's heartbeat"},
+	KindHealth: {Ordered: "by the time the node-engine looked (`at`, on the machine's clock): a statement older " +
+		"than the one kept for that machine is refused, so an event arriving after a newer report does not undo it " +
+		"(novox/hq ADR 0240)",
+		Tests: []string{"TestAnOlderHealthStatementIsRefused"}},
 	KindEnrolment: {Unordered: "a request answered once, under a token spent once: a second presentation is " +
 		"refused by the token, not by an order (issue 083)",
 		Tests: []string{"TestAnEnrolmentMetByAHeldTokenIsAskedToTryAgain"}},