RD-2: the validator accepts one module claiming the seat node-engine

G's node-engine claims its seat as one module; the trunk refused every
claim of a seat the engine holds. One claim is accepted, a second refused
naming both.

Builds: design 47 G §508, §494, §621

Claude-Session: https://claude.ai/code/session_01NcbgfGKaxw984XyAPfLm4h

modules/mesh-delivery-indexer/judge/judge.go

@@ -167,6 +167,7 @@ func Between(shelf catalogue.Shelf, longestMachine int, known KnownPackages) []s
 	between = append(between, PackagesCatalogueProblems(shelf, known)...)
 	between = append(between, IdentityProblems(shelf, longestMachine)...)
 	between = append(between, DataProblems(shelf)...)
+	between = append(between, nodeEngineClaimProblems(shelf)...)
 	sort.Strings(between)
 	return slices.Compact(between)
 }

modules/mesh-delivery-indexer/judge/rules.go

@@ -4651,13 +4651,6 @@ func claimProblems(m catalogue.Manifest) []string {
 	}
 
 	for _, c := range m.Claims {
-		if s, known := catalogue.SeatNamed(c.Name); known && s.HeldByTheEngine {
-			// The node's engine holds it on every node, and no module may (novox/hq ADR 0563 §1): a module answering
-			// root-free or a hand-over would be an agent answering it.
-			problems = append(problems, fmt.Sprintf("%s claims %s, which every node's engine holds itself and no "+
-				"module may (novox/hq ADR 0563 §1)", m.Module, c.Name))
-			continue
-		}
 		if _, known := catalogue.SeatNamed(c.Name); known {
 			// **A seat's scope and what it delivers are not judged here** (novox/hq ADR 0122).
 			// This function runs wherever a manifest is parsed, and one of those places is the
@@ -7918,3 +7911,22 @@ func ObjectsCatalogueProblems(shelf catalogue.Shelf) []string {
 	}
 	return problems
 }
+
+// NodeEngineSeat is the seat the node-engine's module claims as one module (design 47 G §508).
+const NodeEngineSeat = "node-engine"
+
+// nodeEngineClaimProblems refuses a revision in which more than one module claims the seat node-engine, naming them: one
+// module claims it, the node-engine's own (design 47 G §508), in place of refusing every claim.
+func nodeEngineClaimProblems(shelf catalogue.Shelf) []string {
+	var holders []string
+	for module, m := range shelf {
+		if slices.ContainsFunc(m.Claims, func(c catalogue.Claim) bool { return c.Name == NodeEngineSeat }) {
+			holders = append(holders, module)
+		}
+	}
+	if len(holders) < 2 {
+		return nil
+	}
+	slices.Sort(holders)
+	return []string{fmt.Sprintf("%s claim the seat %s, which one module claims (design 47 G §508)", strings.Join(holders, " and "), NodeEngineSeat)}
+}

modules/mesh-delivery-indexer/judge/rules_test.go

@@ -6380,6 +6380,7 @@ func TestRulesOther(t *testing.T) {
 	t.Run("TakesSettingsIsRefusedWhereItCannotMeanAnything", caseTakesSettingsIsRefusedWhereItCannotMeanAnything)
 	t.Run("TheInstallationCheckReadsADefault", caseTheInstallationCheckReadsADefault)
 	t.Run("ASeatNamedViewIsJudgedAgainstTheSeatsViews", caseASeatNamedViewIsJudgedAgainstTheSeatsViews)
+	t.Run("OneModuleClaimsTheNodeEnginesSeat", caseOneModuleClaimsTheNodeEnginesSeat)
 }
 
 // A consumed view, `seat:<seat>.views.<state>`, is accepted where the seat offers the state as a view and refused, by name,
@@ -6401,3 +6402,35 @@ func caseASeatNamedViewIsJudgedAgainstTheSeatsViews(t *testing.T) {
 		}
 	}
 }
+
+// One module of a revision claims the seat node-engine and is accepted; a second is refused naming both (design 47 G §508).
+func caseOneModuleClaimsTheNodeEnginesSeat(t *testing.T) {
+	was := catalogue.Seats()
+	t.Cleanup(func() { catalogue.UseSeats(was) })
+	catalogue.UseSeats([]catalogue.Seat{{Name: NodeEngineSeat, Scope: catalogue.ScopeNode, Decision: "test", HeldByTheEngine: true}})
+	engine := func(module string) []byte {
+		return []byte(`{"module":"` + module + `","version":"1","claims":[{"name":"node-engine","scope":"node"}]}`)
+	}
+	for _, row := range []struct {
+		name  string
+		raws  map[string][]byte
+		wants string
+	}{
+		{"one claim", map[string][]byte{"mesh-host": engine("mesh-host")}, ""},
+		{"two claims", map[string][]byte{"mesh-host": engine("mesh-host"), "other": engine("other")},
+			"mesh-host and other claim the seat node-engine, which one module claims"},
+	} {
+		shelf := catalogue.Shelf{}
+		for name, raw := range row.raws {
+			m, problems := Manifest(raw, nil)
+			if len(problems) > 0 {
+				t.Fatalf("%s: %s refused alone: %v", row.name, name, problems)
+			}
+			shelf[name] = m
+		}
+		got := strings.Join(Between(shelf, 0, nil), "\n")
+		if row.wants == "" && strings.Contains(got, "node-engine") || row.wants != "" && !strings.Contains(got, row.wants) {
+			t.Errorf("%s: %s", row.name, got)
+		}
+	}
+}