A settle ask's group and the act its options bind, shared by the gate and the teller (ADR 0556 clause 5)

go/delivery/gate.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"reflect"
 	"regexp"
+	"sort"
 	"strconv"
 	"strings"
 
@@ -87,6 +88,29 @@ func MergeAskKey(group string, heads []Head) (string, error) {
 	return AskKindMerge + "." + part + "." + hash, nil
 }
 
+// SettleGroupPrefix begins the group of a settle ask (novox/hq ADR 0556 clause 5): a person's ask to settle deliveries held
+// because their merge reached the trunk without a passing check. It is kept in the gate's asks under MergeAskKey like a merge
+// ask, so the teller carries it unchanged; its options bind the act AskVerb names for it.
+const SettleGroupPrefix = "settle/"
+
+// SettleGroup is the group of the settle ask of these delivery ids: the prefix and twelve hex digits of the sha256 over the
+// ids, sorted and joined by a newline, so the same deliveries asked again keep one key.
+func SettleGroup(ids []string) string {
+	sorted := append([]string(nil), ids...)
+	sort.Strings(sorted)
+	sum := sha256.Sum256([]byte(strings.Join(sorted, "\n")))
+	return SettleGroupPrefix + hex.EncodeToString(sum[:])[:12]
+}
+
+// AskVerb is the act the options of an ask of the gate bind, by its group: a settle ask's `mesh-delivery.settle`, any other
+// `mesh-delivery.merge`. The gate composes the act with it and the teller checks a warrant against it.
+func AskVerb(group string) string {
+	if strings.HasPrefix(group, SettleGroupPrefix) {
+		return "mesh-delivery.settle"
+	}
+	return "mesh-delivery.merge"
+}
+
 // ParseAskKey is the inverse of MergeAskKey: the kind, the group and the heads hash.
 func ParseAskKey(key string) (kind, group, hash string, err error) {
 	parts := strings.Split(key, ".")

go/delivery/gate_test.go

@@ -77,6 +77,18 @@ func TestAskID(t *testing.T) { // 1201/AC2
 	if AskID(k1) != AskID(k1) {
 		t.Error("the id is not stable")
 	}
+	// 1280 (ADR 0556 clause 5): a settle ask's group is the same for the same ids in any order, keys like any group, and its
+	// options bind mesh-delivery.settle; every other ask binds mesh-delivery.merge.
+	g := SettleGroup([]string{"novox/b@222222222222", "novox/a@111111111111"})
+	if g != SettleGroup([]string{"novox/a@111111111111", "novox/b@222222222222"}) || !strings.HasPrefix(g, SettleGroupPrefix) || len(g) != len(SettleGroupPrefix)+12 {
+		t.Errorf("SettleGroup = %q", g)
+	}
+	if k, err := MergeAskKey(g, gateHeads()); err != nil || !asks.UsableID(AskID(k)) {
+		t.Errorf("the settle ask's key %q: %v", k, err)
+	}
+	if AskVerb(g) != "mesh-delivery.settle" || AskVerb("feat/x") != "mesh-delivery.merge" {
+		t.Errorf("AskVerb = %q, %q", AskVerb(g), AskVerb("feat/x"))
+	}
 }
 
 func TestOwedKey(t *testing.T) { // 1201/AC3