node-engine client: the node key of the have, the codecs of the health report and of the data items (ADR 0634 §1, §4; issue 1966)

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

go/clients/nodeengineclient/keys.go

@@ -120,3 +120,11 @@ func ParseComposedKey(key string) (node, module, fingerprintPart string, isNode
 	}
 	return refused(fmt.Errorf("the key has %d parts", len(parts)))
 }
+
+// HaveNodeKey is the key, in the state have, of a node's own facts: `<node>.node`.
+func HaveNodeKey(node string) (string, error) {
+	if err := keys.CheckName("node", node); err != nil {
+		return "", err
+	}
+	return node + "." + NodeWord, nil
+}