Group the sources into aliased modules and lint with the published plugins

src/common/json.ts

@@ -0,0 +1,12 @@
+// Type guards for values read from JSON, which arrive as `unknown`.
+export type JsonObject = NodeJS.Dict<unknown>;
+
+// Any non-null object, arrays included: reading a missing key yields undefined.
+export function isObject(value: unknown): value is JsonObject {
+  return typeof value === "object" && value !== null;
+}
+
+// A plain mapping, which an array is not.
+export function isMapping(value: unknown): value is JsonObject {
+  return isObject(value) && !Array.isArray(value);
+}