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/serve.go

@@ -94,6 +94,8 @@ type Server struct {
 	retirements Retirements
 	// checker asks for a pull request's merge check (novox/hq to-be 45 §9).
 	checker Checker
+	// healths keeps what machines say of their long-running resources (novox/hq ADR 0240).
+	healths Healths
 
 	log *log.Logger
 	// giveUp is how long one message is held for the store; zero means GiveUpAfter.
@@ -194,6 +196,8 @@ func (s *Server) act(ctx context.Context, m Control) {
 		s.heartbeat(m)
 	case KindToolsHeartbeat:
 		s.toolsHeartbeat(m)
+	case KindHealth:
+		s.healthSaid(ctx, m)
 	case KindBuilt:
 		s.wasBuilt(ctx, m)
 	case KindModuleMoved: