fix(storage): recognize errors across module packages

packages/contracts/src/module-storage.ts

@@ -87,6 +87,28 @@ export class ModuleStorageError extends Error {
   }
 }
 
+/**
+ * Whether `value` is a module-storage error, judged by its stable public shape rather than its class.
+ *
+ * An installed module bundles its own copy of the contracts package (ADR 0049), so an error created
+ * by the host's storage provider does not share class identity with the module's
+ * `ModuleStorageError`. `instanceof ModuleStorageError` is therefore not a valid check across the
+ * module boundary.
+ */
+export function isModuleStorageError(
+  value: unknown,
+): value is Pick<ModuleStorageError, "code" | "key" | "message" | "name"> {
+  if (!(value instanceof Error) || value.name !== "ModuleStorageError") {
+    return false;
+  }
+  const { code, key } = value as { code?: unknown; key?: unknown };
+  return (
+    typeof code === "string" &&
+    (MODULE_STORAGE_ERROR_CODES as readonly string[]).includes(code) &&
+    (key === undefined || typeof key === "string")
+  );
+}
+
 /** The S3 object-key ceiling, which every S3-compatible provider shares. Measured in UTF-8 bytes,
  * not characters, because that is what the wire format bounds. */
 export const MODULE_STORAGE_KEY_MAX_BYTES = 1024;