Compare the have's user list by what it says, so a have is not written again for the same list (ADR 0547 §8)

go/delivery/delivery.go

@@ -491,7 +491,19 @@ func DecodePulse(data []byte) (Pulse, error) {
 }
 
 // SameHave says whether two haves are the same value, so a writer writes only when they differ.
-func SameHave(a, b Have) bool { return a == b }
+func SameHave(a, b Have) bool {
+	ua, ub := a.UserList, b.UserList
+	a.UserList, b.UserList = nil, nil
+	if a != b || (ua == nil) != (ub == nil) {
+		return false
+	}
+	if ua == nil {
+		return true
+	}
+	x, y := *ua, *ub
+	x.At, y.At = time.Time{}, time.Time{}
+	return x == y && ua.At.Equal(ub.At)
+}
 
 // SameHaveNode says whether two node facts are the same value, comparing each carried JSON without its spacing.
 func SameHaveNode(a, b HaveNode) bool {

go/delivery/delivery_test.go

@@ -294,6 +294,18 @@ func TestSame(t *testing.T) {
 	if SameHave(a, b) {
 		t.Error("different haves same")
 	}
+	// The user list is compared by what it says, never by where it is held (ADR 0547 §8).
+	at := time.Date(2026, 10, 25, 21, 0, 0, 0, time.UTC)
+	ua, ub := a, a
+	ua.UserList = &UserListWritten{Source: "k", Revision: 1, Wanted: "sha256:a", Digest: "sha256:a", Users: 2, At: at}
+	ub.UserList = &UserListWritten{Source: "k", Revision: 1, Wanted: "sha256:a", Digest: "sha256:a", Users: 2, At: at.In(time.Local)}
+	if !SameHave(ua, ub) || SameHave(ua, a) {
+		t.Error("equal user lists differ, or one said and one not are the same")
+	}
+	ub.UserList.Revision = 2
+	if SameHave(ua, ub) {
+		t.Error("different user lists same")
+	}
 	n := HaveNode{V: 1, Busy: json.RawMessage(`true`)}
 	if !SameHaveNode(n, HaveNode{V: 1, Busy: json.RawMessage(`true`)}) || SameHaveNode(n, HaveNode{V: 1}) {
 		t.Error("have node")