Keep a condition's looks in the store, so a look that changes nothing writes no bucket (issue 420)

Every look rewrote the condition's value in the conditions bucket, because the
value carried the count of looks, the last look and the newest evidence: 131 647
writes in four days for twelve open conditions, against ADR 0289's rule that a
bucket is written only when what it describes changed. The looks now live in the
controller's store (migration 0095, condition_looks), the bucket holds what a
condition says and is written only when that changes, and the conditions verb and
the condition events put the looks back.

cmd/mesh-controller/conditions.go

@@ -24,16 +24,18 @@ import (
 // **`status` used to be the only place the mesh said it was wrong, and only to whoever asked.** Every
 // core failure of research 031 was found by a person looking. A condition is the mesh saying it: raised
 // by a watchdog when a signal is late (signals.go), by a probe when an invariant does not hold
-// (doctor.go), or by an event a provider sends (standing.go); kept on the bus with since-when and
-// evidence; said on the bus as it changes, for the operator's channel to carry; and cleared when an
+// (doctor.go), or by an event a provider sends (standing.go); kept on the bus with since-when, and its
+// looks — how often, when last, the newest evidence — in the controller's store (condition_looks.go,
+// novox/hq issue 420); said on the bus as it changes, for the operator's channel to carry; and cleared when an
 // observation says it is resolved. Nobody resolves one by hand. A person who knows silences it, for a
 // while, with a reason, and that is recorded as a hand act.
 
 // conditionsFrom is the serving controller's keeper; nil in any other process, which opens its own.
 var conditionsFrom *conditions.Keeper
 
-// keeperOn is a keeper over the store on a connection, saying its transitions on that connection.
-func keeperOn(ctx context.Context, conn *nats.Conn) (*conditions.Keeper, error) {
+// keeperOn is a keeper over the store on a connection, saying its transitions on that connection, with
+// the conditions' looks kept in looks (condition_looks.go).
+func keeperOn(ctx context.Context, conn *nats.Conn, looks conditions.LookStore) (*conditions.Keeper, error) {
 	store, history, err := conditions.OnTheBus(ctx, conn)
 	if err != nil {
 		return nil, err
@@ -42,7 +44,7 @@ func keeperOn(ctx context.Context, conn *nats.Conn) (*conditions.Keeper, error)
 	if err != nil {
 		return nil, err
 	}
-	return conditions.NewKeeper(ctx, conditions.Options{Store: store, History: history,
+	return conditions.NewKeeper(ctx, conditions.Options{Store: store, History: history, Looks: looks,
 		Teller: link.OverNATS{Conn: conn, JS: js},
 		Say:    func(format string, args ...any) { fmt.Fprintf(os.Stderr, format+"\n", args...) },
 		// What status leads with changed: composed again soon (a nudge outside the serving controller
@@ -58,8 +60,10 @@ func withKeeper(ctx context.Context, f func(*conditions.Keeper) error) error {
 	if conditionsFrom != nil {
 		return f(conditionsFrom)
 	}
+	looks, closeLooks := looksHere(ctx)
+	defer closeLooks()
 	return onTheBus(func(conn *nats.Conn) error {
-		k, err := keeperOn(ctx, conn)
+		k, err := keeperOn(ctx, conn, looks)
 		if err != nil {
 			return err
 		}
@@ -82,6 +86,8 @@ func openConditions(ctx context.Context) ([]conditions.Condition, error) {
 		return nil, fmt.Errorf("this process has no bus to read the conditions from: %w", err)
 	}
 	var out []conditions.Condition
+	looks, closeLooks := looksHere(ctx)
+	defer closeLooks()
 	err := onTheBus(func(conn *nats.Conn) error {
 		store, _, err := conditions.OnTheBus(ctx, conn)
 		if err != nil {
@@ -89,7 +95,7 @@ func openConditions(ctx context.Context) ([]conditions.Condition, error) {
 		}
 		reading, cancel := context.WithTimeout(ctx, 5*time.Second)
 		defer cancel()
-		out, err = conditions.Read(reading, store)
+		out, err = conditions.ReadWith(reading, store, looks)
 		return err
 	})
 	return out, err
@@ -252,12 +258,14 @@ func showCondition(ctx context.Context, args []string, w io.Writer) error {
 	if conditionsFrom != nil {
 		c, found, err = conditionsFrom.Get(ctx, key)
 	} else {
+		looks, closeLooks := looksHere(ctx)
+		defer closeLooks()
 		err = onTheBus(func(conn *nats.Conn) error {
 			store, _, err := conditions.OnTheBus(ctx, conn)
 			if err != nil {
 				return err
 			}
-			c, found, err = conditions.ReadOne(ctx, store, key)
+			c, found, err = conditions.ReadOneWith(ctx, store, looks, key)
 			return err
 		})
 	}