Act under a lease, keep accounts by order, one writer at composition (hq to-be 45 Phase 2)

Two controllers could both act (issue 204), a reconcile's report could
overtake the apply after it and the digest decided (issue 267), and a grant
could make a second writer of a machine's report.

- The lease (internal/lease, ADR 0229): mesh-controller_lease key `holder`,
  15 s age, renewed every 5 s by compare-and-set; the epoch is the revision
  it was taken at. The gate is the clock (stops 3 s before expiry); a refused
  renewal is a loss and the process exits; a holder that stops gives it back.
  serve takes it before asserting the bus. Epochs kept in the store
  (migration 0068 controller_epoch) as a floor: a bucket raised from nothing
  is compacted past it. Unleased (no epoch, S12 urgent) only when nobody
  holds it and the bus will not let it be written. A shell command acts
  under the holder's epoch, or its own lease when none.
- Declarations carry `epoch` inside the signed envelope, only to a machine
  whose latest account carried a report_sequence (mesh-host #35); would-send
  is composed with the epoch last sent. Allot and the send both pass the gate.
- Reports: contract in internal/link/order.go (epoch, sequence,
  report_sequence, older_than, refused_older). Accounts kept by epoch, then
  sequence, then report sequence; older refused, counted; unordered reports
  keep the digest rule. Plans by compare-and-set on a revision, with epoch.
  Conditions and calls carry the epoch and are not written off the lease.
- S12 and S13 (naming the writer by epoch) watched, D5 run; reset of the
  bucket said. Writers table compiled in and enforced in PermissionsFor; the
  controller no longer publishes mesh.control.>. A contract per consumed
  kind, and the empty-on-error lint over the repository.
- mesh-host pinned to its main with the epoch in the validator (D1 validates
  the envelope as sent).

Needs mesh-host's genesis lock with the lease grant (mesh-host PR) for
TestTheInstallersFirstUserListIsWhatTheControllerWouldCompose.

internal/broker/controller_buckets.go

@@ -31,8 +31,15 @@ var (
 	HandActsBucket         = BucketName(ControllerSeat, "hand-acts")
 	ConditionsBucket       = BucketName(ControllerSeat, "conditions")
 	ConditionHistoryBucket = BucketName(ControllerSeat, "condition-history")
+	// LeaseBucket holds the controller's lease (to-be 45 §6): one key, `holder`, which the instance
+	// allowed to act writes by compare-and-set and renews; its revision when taken is the epoch.
+	LeaseBucket = BucketName(ControllerSeat, "lease")
 )
 
+// LeaseTTL is how long the lease's key lives unrenewed (to-be 45 §6): fifteen seconds, renewed
+// every five. The bucket's age, so the bus forgets a holder that stopped renewing.
+const LeaseTTL = 15 * time.Second
+
 // The bounds to-be 45 §6 sets for calls: the last thousand, or fourteen days, whichever is fewer.
 // A call is two keys — its record, and its answer apart so a listing does not read every answer —
 // so the stream holds twice as many messages as it keeps calls.
@@ -52,12 +59,12 @@ const (
 // IsControllerBucket says a bucket is the controller's own, not a module's state nothing declares.
 func IsControllerBucket(bucket string) bool {
 	return bucket == CallsBucket || bucket == HandActsBucket || bucket == ConditionsBucket ||
-		bucket == ConditionHistoryBucket
+		bucket == ConditionHistoryBucket || bucket == LeaseBucket
 }
 
 // ControllerBuckets are the controller's own buckets, in the order they are asserted.
 func ControllerBuckets() []string {
-	return []string{CallsBucket, HandActsBucket, ConditionsBucket, ConditionHistoryBucket}
+	return []string{LeaseBucket, CallsBucket, HandActsBucket, ConditionsBucket, ConditionHistoryBucket}
 }
 
 // ControllerBucketsAsserter is what raising the controller's buckets needs of a connection.
@@ -74,6 +81,9 @@ func (j *JetStream) EnsureControllerBuckets() error {
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()
+	if err := EnsureLeaseBucket(ctx, js); err != nil {
+		return err
+	}
 	if _, err := js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
 		Bucket: CallsBucket,
 		Description: "the calls of the mesh's own verbs and what came of each (novox/hq to-be 45 §6, issue " +
@@ -141,3 +151,24 @@ func (j *JetStream) EnsureControllerBuckets() error {
 	}
 	return nil
 }
+
+// EnsureLeaseBucket creates the lease's bucket if absent and brings its options to match (to-be 45
+// §6). **Before the lease is taken, by any candidate**: it is the lease's own precondition, and asserting
+// a bucket that exists changes nothing. File storage, so its revisions — the epochs — outlive a restart of
+// the bus; one raised again from nothing is moved past the highest epoch issued when the lease is taken.
+func EnsureLeaseBucket(ctx context.Context, js jetstream.JetStream) error {
+	if _, err := js.CreateOrUpdateKeyValue(ctx, jetstream.KeyValueConfig{
+		Bucket: LeaseBucket,
+		Description: "the controller's lease (novox/hq to-be 45 §6): the key `holder`, written by compare-and-set " +
+			"by the one controller instance that may act and renewed every five seconds; its revision when taken " +
+			"is the epoch every declaration and plan write carries",
+		History:      1,
+		TTL:          LeaseTTL,
+		MaxValueSize: 4 << 10,
+		MaxBytes:     1 << 20,
+		Storage:      jetstream.FileStorage,
+	}); err != nil {
+		return fmt.Errorf("asserting bucket %s: %w", LeaseBucket, err)
+	}
+	return nil
+}