Take a walk's modules from the builder's done keys and ask no build but the builder's own: a key building or unreferenced holds the tier and says so, a failed key fails the walk in its words (issue 1851, A6, A7)

cmd/mesh-controller/ask_bus_moment_test.go

@@ -15,6 +15,15 @@ import (
 // seconds) is not a failed build. The module is left unasked and the plan building, and the next look asks it again; only a
 // module's own fault, or a bus silent for ten minutes, fails the plan.
 
+// asksOfEveryModule makes every module a test names the builder's own, the one module a walk still asks build-agent
+// for (ADR 0453 §5): what a test of that ask's waits reads.
+func asksOfEveryModule(t *testing.T) {
+	t.Helper()
+	was := buildersOwn
+	buildersOwn = func(string) bool { return true }
+	t.Cleanup(func() { buildersOwn = was })
+}
+
 func aTierOfThree() (*inventory.Plan, map[string]inventory.Entry) {
 	p := &inventory.Plan{ID: "plan-1", State: inventory.PlanBuilding, Tiers: [][]string{{"a", "b", "c"}},
 		Modules: map[string]*inventory.PlanModule{}}
@@ -26,6 +35,7 @@ func aTierOfThree() (*inventory.Plan, map[string]inventory.Entry) {
 }
 
 func TestABusThatDoesNotAnswerForAMomentDoesNotFailTheTier(t *testing.T) {
+	asksOfEveryModule(t)
 	p, byName := aTierOfThree()
 	bus := false
 	was := askABuild
@@ -68,6 +78,7 @@ func TestABusThatDoesNotAnswerForAMomentDoesNotFailTheTier(t *testing.T) {
 }
 
 func TestABusSilentForTenMinutesFailsTheTierAsBefore(t *testing.T) {
+	asksOfEveryModule(t)
 	p, byName := aTierOfThree()
 	was := askABuild
 	askABuild = func(context.Context, buildSource, string, string) (string, error) {
@@ -119,6 +130,7 @@ func TestAPlanWithAModuleWaitingForTheBusIsOneTheLookComesBackTo(t *testing.T) {
 }
 
 func TestAModulesOwnFaultStillFailsThePlan(t *testing.T) {
+	asksOfEveryModule(t)
 	p, byName := aTierOfThree()
 	delete(byName, "a")
 	askModule(t.Context(), p, "a", byName)