fix(node-sdk): keep flagStateVersion backward compatible

Author: roncohen

packages/node-sdk/src/client.ts

@@ -525,11 +525,13 @@ export class ReflagClient {
           path,
           this._config.flagsFetchRetries,
         );
+        const flagStateVersion = res?.flagStateVersion;
         if (
           !isObject(res) ||
           !Array.isArray(res?.features) ||
-          !Number.isInteger(res?.flagStateVersion) ||
-          res.flagStateVersion < 0
+          typeof flagStateVersion !== "number" ||
+          !Number.isInteger(flagStateVersion) ||
+          flagStateVersion < 0
         ) {
           const fallbackDefinitions = await this.loadFlagsFallbackDefinitions();
           return fallbackDefinitions
@@ -541,7 +543,7 @@ export class ReflagClient {
         this.canLoadFlagsFallbackProvider = false;
         return {
           definitions: compileFlagDefinitions(res.features),
-          flagStateVersion: res.flagStateVersion,
+          flagStateVersion,
         };
       },
       {

packages/node-sdk/src/types.ts

@@ -373,9 +373,10 @@ export type FlagAPIResponse = {
  */
 export type FlagsAPIResponse = {
   /**
-   * Monotonic version of the flag state snapshot returned by the backend.
+   * Optional for backward compatibility; when absent, the snapshot version
+   * should be treated as unknown by consumers.
    */
-  flagStateVersion: number;
+  flagStateVersion?: number;
 
   /**
    * The feature definitions.