feat(nest): @-addressing, addressed-crow-must-respond, deliver back to requester (#11)

brain.go

@@ -233,6 +233,8 @@ func (MockBrain) Ask(ctx context.Context, system, prompt string) (string, int, e
 	switch {
 	case strings.Contains(system, markerBanter):
 		return "[mock] Caw.", tokens, nil
+	case strings.Contains(system, markerNestReply):
+		return "KIND: deliver\n[mock] handled: " + after(prompt, "TASK:"), tokens, nil
 	case strings.Contains(system, markerSentry):
 		return mockTriage(after(prompt, "ITEM:")), tokens, nil
 	case strings.Contains(system, markerElder):