Apply a module again only for a newly missing resource, leave filled files out of the record check, and say when the applied state cannot be read (issue 1945)

cmd/mesh-host/main.go

@@ -1334,6 +1334,7 @@ const (
 // anyway. A statement the bus did not take is said at the next look. It reads; it never acts (ADR 0240
 // rule 6) — but for going on with a take act stopped at its bound (ADR 0328 §7), which runs beside it.
 func judgeWhatRuns(ctx context.Context, j *liveness.Judge, queue *link.Session, say link.Announce, reapply func(modules ...string)) {
+	var missingBefore map[string]bool
 	ticker := time.NewTicker(liveness.LookEvery)
 	defer ticker.Stop()
 	var lastSaid time.Time
@@ -1421,7 +1422,9 @@ func judgeWhatRuns(ctx context.Context, j *liveness.Judge, queue *link.Session,
 			}
 			// A resource the machine does not have at all is made again: its module's composition applied anew (issue
 			// 1945), once each time the statement changes, never on a clock.
-			if m := missingModules(st); len(m) > 0 && reapply != nil {
+			var m []string
+			m, missingBefore = newlyMissing(missingBefore, st)
+			if len(m) > 0 && reapply != nil {
 				say(fmt.Sprintf("applying %s again: a resource it declares is not on this machine", strings.Join(m, ", ")))
 				reapply(m...)
 			}
@@ -2101,3 +2104,21 @@ func missingModules(st liveness.Statement) []string {
 	sort.Strings(out)
 	return out
 }
+
+// newlyMissing are the modules of the resources a statement says missing that the last statement acted on did not, each
+// once, sorted, and the missing resources now: a resource still missing is not acted on again, so a module whose
+// resource cannot be made is not applied at every change of the statement (the review of issue 1945).
+func newlyMissing(last map[string]bool, st liveness.Statement) ([]string, map[string]bool) {
+	now := map[string]bool{}
+	var fresh liveness.Statement
+	for _, r := range st.Resources {
+		if !r.Missing {
+			continue
+		}
+		now[r.ID] = true
+		if !last[r.ID] {
+			fresh.Resources = append(fresh.Resources, r)
+		}
+	}
+	return missingModules(fresh), now
+}