A group member's own check runs its repository's check alone, a cycle fails the composed check, and mark-ready leaves the delivery seat (issue 977, part D, ADR 0403)

cmd/mesh-controller/check_siblings.go

@@ -127,10 +127,15 @@ func siblingsFor(p link.PullUpdated, entries []inventory.Entry, beside map[strin
 // could not be learned (ADR 0382 §1): a check never waits on mesh-delivery past groupAskWithin and never fails for it,
 // so a fix to mesh-delivery is still checked without it.
 func withSiblings(ctx context.Context, request *link.BuildRequest, p link.PullUpdated, entries []inventory.Entry) {
+	lines, err := groupsAsked(ctx, deliverySeatHeld(entries))
+	siblingsFrom(request, p, entries, lines, err)
+}
+
+// siblingsFrom is withSiblings from mesh-delivery's answer already had.
+func siblingsFrom(request *link.BuildRequest, p link.PullUpdated, entries []inventory.Entry, lines []groupsLine, err error) {
 	if request.Check == nil {
 		return
 	}
-	lines, err := groupsAsked(ctx, deliverySeatHeld(entries))
 	if err != nil {
 		request.Check.SiblingsUnknown = fmt.Sprintf("mesh-delivery did not say the group's pull requests (%v): "+
 			"the check reads no siblings", err)
@@ -138,3 +143,23 @@ func withSiblings(ctx context.Context, request *link.BuildRequest, p link.PullUp
 	}
 	request.Check.Siblings, request.Check.SiblingsUnknown = siblingsFor(p, entries, request.Check.Beside, lines)
 }
+
+// composedMember says the pull request is a member of a delivery group whose gate is the composed check's (novox/hq
+// ADR 0403 clauses 1 and 7): the group has two members or more and mesh-delivery says so on its line. The group is
+// found as siblingsFor finds it, by its head branch name, or, for a recheck that carries none, by the pull request's
+// repository and number — not by siblings, which name only what the check reads beside it.
+func composedMember(p link.PullUpdated, lines []groupsLine) bool {
+	own := strings.ToLower(p.Owner + "/" + p.Repo)
+	for _, l := range lines {
+		found := p.Head != "" && l.ID == p.Head
+		for _, m := range l.Details {
+			if p.Head == "" && p.Number != 0 && m.Number == p.Number && strings.ToLower(m.Repository) == own {
+				found = true
+			}
+		}
+		if found {
+			return l.ComposedGate && max(len(l.Details), len(l.Members)) >= 2
+		}
+	}
+	return false
+}