Subscribe as soon as the runtime serves, never after a guessed wait, so no event sent at a start is missed (issue 774)

mesh-healers slept 2 s before its first subscribe to the keeper's conditions; its whole test delivered
condition-raised once the lease was read, often before that, and the event was dropped: "never: the would-act
written" in about two runs of three on main, failing the group check. Eight modules had the same shape.

Quick fix: sleep after a failed subscribe in mesh-healers alone.
Thorough fix (chosen, the kind is in eight modules): every loop that asks the runtime for events or a watch
waits for stdio.Served() and subscribes at once, sleeping only after a refusal (mesh-healers, mesh-config,
mesh-mail, mesh-issues, mesh-provisioner, mesh-watcher, mesh-delivery-gate); mesh-knowledge, whose pinned
mesh-sdk has no Served, subscribes first and sleeps after a refusal. The healers' whole test delivers the
event only once the bundle has subscribed it, as the runtime's consumer holds it until then.

modules/mesh-knowledge/cmd/mesh-knowledge/main.go

@@ -114,7 +114,6 @@ func callerOf(args map[string]any) string { return stdio.CallerOf(args) }
 // hear subscribes to the router's word on this module's asks, asked again until the runtime takes it.
 func hear(k *KB) {
 	for wait := 2 * time.Second; ; wait = min(wait*2, time.Minute) {
-		time.Sleep(wait)
 		err := stdio.Subscribe(asks.Seat+".decided."+Module, func(e stdio.Envelope) error {
 			var w asks.Warrant
 			if json.Unmarshal(e.Body, &w) == nil {
@@ -127,6 +126,7 @@ func hear(k *KB) {
 			return
 		}
 		logf("[mesh-knowledge] does not hear the operator's answers yet (%v); asking again in %s", err, wait)
+		time.Sleep(wait)
 	}
 }