Follow config from a durable consumer, compose again only what changed since, and hold the node only for a write (issue 1945, ADR 0545, review)

The start composed every kept composition of every module on every node, each a
whole node composed in memory under the node's lock: 10 to 50 minutes at a
start, holding take-ins back. Now the writes of mesh-config_resolved are read
from the durable consumer mesh-controller-config-follow, acknowledged once the
change is composed, so a restart composes again only what was written since
the last change handled, and a first start nothing it did not hear. The node's
lock is taken for each write alone. A consumer that cannot be made or read
raises config-not-followed and is tried again a minute later, cleared once it
reads. The controller's account is granted that consumer's acknowledgements
where mesh-config serves, as its verb is.
Research 072: milestone 2, the composer reacting to the change of an input.

internal/broker/composed.go

@@ -190,3 +190,7 @@ const TakeInConsumer = "mesh-controller-take-in"
 // TakeInBuckets are the buckets the take-in consumes: the indexer's modules (each module's trunk value) and the builder's
 // builds (each build's key).
 var TakeInBuckets = []string{delivery.ModulesBucket, delivery.BuilderBuildsBucket}
+
+// ConfigFollowConsumer is the durable consumer the controller follows mesh-config's resolved values with, on that
+// bucket's stream (novox/hq ADR 0545).
+const ConfigFollowConsumer = "mesh-controller-config-follow"

internal/broker/nats.go

@@ -1273,6 +1273,11 @@ func PermissionsFor(p Principal) (Permissions, error) {
 				pub = append(pub, "mesh.seat."+v.Seat+"."+CallKind+"."+v.Verb+"."+CallerToken(p.Username()))
 			}
 		}
+		// And its consumer of mesh-config's resolved values, acknowledged once a change is composed (novox/hq ADR 0545):
+		// where mesh-config serves, as its verb, so genesis grants nothing of mesh-config.
+		if len(p.AsksTheConfig) > 0 {
+			pub = append(pub, "$JS.ACK.KV_"+ConfigResolvedBucket+"."+ConfigFollowConsumer+".>")
+		}
 	}
 
 	sort.Strings(pub)