buildrun: open a steps watch again that closed having heard nothing, up to 3 closes in a row

A watch that closed at once was left for good, so an ask whose own watch
went deaf was read only at a reconnect (review of fix/lost-check).

go/delivery/buildrun/heardends.go

@@ -175,8 +175,7 @@ func (s JetStreamAsks) AskSteps(ctx context.Context, module, askID string) ([]de
 
 // HearEnds is the HeardEnds every asker of the build seats waits through: over inner (the asks' own watches, or a
 // LostAskWaiter's inner), reading with asks, and nudged at each step end of each of modules (one watch of each steps state,
-// updates only; one that closes is opened again while it heard something since it was opened, and said and left
-// otherwise). The asker nudges it at a reconnect too (Nudge("")).
+// updates only; one that closes is opened again, and said and left after reopenTries closes in a row that heard nothing). The asker nudges it at a reconnect too (Nudge("")).
 func HearEnds(ctx context.Context, asks JetStreamAsks, inner AskWaiter, modules []string, logf func(string, ...any)) *HeardEnds {
 	if logf == nil {
 		logf = func(string, ...any) {}
@@ -194,6 +193,7 @@ func HearEnds(ctx context.Context, asks JetStreamAsks, inner AskWaiter, modules
 }
 
 func (h *HeardEnds) follow(ctx context.Context, kv jetstream.KeyValue, module string) {
+	silent := 0 // closes in a row having heard nothing
 	for ctx.Err() == nil {
 		w, err := kv.WatchAll(ctx, jetstream.UpdatesOnly())
 		if err != nil {
@@ -215,8 +215,10 @@ func (h *HeardEnds) follow(ctx context.Context, kv jetstream.KeyValue, module st
 			return
 		}
 		h.Nudge(module) // a step may have ended while the watch was closing
-		if !heard {
-			h.logf("the watch of the steps of %s closed having heard nothing, so it is left: an ask whose own watch goes deaf is read only at a reconnect", module)
+		if heard {
+			silent = 0
+		} else if silent++; silent >= reopenTries {
+			h.logf("the watch of the steps of %s closed %d times in a row having heard nothing, so it is left: an ask whose own watch goes deaf is read only at a reconnect", module, silent)
 			return
 		}
 		h.logf("the watch of the steps of %s closed; opened again", module)