mesh-delivery-checker: a composer at the node-engine's head that cannot run fails the composition

Review finding 3 (ADR 0593 §9): only a node that does not answer may let a check pass with a warning; a
sandbox composer that cannot be built or run was filed with the silent nodes. It now fails that node's
composition, naming the head.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/mesh-delivery-checker/internal/check/engines.go

@@ -91,8 +91,15 @@ func (e EngineCompositions) Compose(ctx context.Context, c *Case) (delivery.Comp
 			defer cancel()
 			a, err := e.Asker.ComposeCandidate(at, node, delivery.ComposeCandidateAsk{Candidate: key, Input: sandboxed})
 			if err == nil && sandboxed && a.Verdict != delivery.ComposeCandidateUnready {
-				// The composer's build and run are the check's to bound, not the engine's answer bound.
-				a, err = e.inSandbox(ctx, c, head, node, a)
+				// The composer's build and run are the check's to bound, not the engine's answer bound. A composer that
+				// cannot run is no silent node (ADR 0593 §9 lets only that pass): the node's composition fails, naming
+				// the head.
+				if composed, serr := e.inSandbox(ctx, c, head, node, a); serr != nil {
+					a = delivery.ComposeCandidateAnswer{V: a.V, Node: node, Candidate: a.Candidate, Verdict: delivery.ComposeCandidateRefused,
+						Refused: "the composer at the node-engine's head " + head + " could not compose it: " + serr.Error()}
+				} else {
+					a = composed
+				}
 			}
 			mu.Lock()
 			defer mu.Unlock()

modules/mesh-delivery-checker/internal/check/engines_test.go

@@ -45,6 +45,7 @@ type fakeSandbox struct {
 	mu   sync.Mutex
 	jobs []delivery.ComposeJob
 	v    func(node string) composer.Verdict
+	err  error
 }
 
 func (f *fakeSandbox) Compose(_ context.Context, job delivery.ComposeJob) (composer.Verdict, error) {
@@ -55,6 +56,9 @@ func (f *fakeSandbox) Compose(_ context.Context, job delivery.ComposeJob) (compo
 	f.mu.Lock()
 	f.jobs = append(f.jobs, job)
 	f.mu.Unlock()
+	if f.err != nil {
+		return composer.Verdict{}, f.err
+	}
 	return f.v(req.Machines[0]), nil
 }
 
@@ -164,5 +168,14 @@ func TestTheCompositionIsMadeFromTheEnginesAnswers(t *testing.T) {
 		if v.State != delivery.CompositionFail || v.SDK != head2 || !strings.Contains(v.Words, "the new composer refuses it") {
 			t.Errorf("verdict = %+v", v)
 		}
+		// Review finding 3 (ADR 0593 §9 lets only a node that does not answer pass): a composer at the head that cannot
+		// run fails the composition, naming the head, never passing as a silent node.
+		sb.err = errors.New("the build of mesh-compose failed")
+		v, err = ec.Compose(context.Background(), host)
+		if err != nil || v.State != delivery.CompositionFail || !strings.Contains(v.Words, head2) ||
+			!strings.Contains(v.Words, "the build of mesh-compose failed") || len(v.Warnings) != 0 {
+			t.Errorf("a composer that cannot run: %+v, %v", v, err)
+		}
 	})
+
 }