fix: Do not cache rejected KV loads in Fastly EdgeFeatureStore (#1796)

Author: keelerm84

packages/sdk/fastly/__tests__/api/EdgeFeatureStore.test.ts

@@ -113,6 +113,30 @@ describe('EdgeFeatureStore', () => {
     });
   });
 
+  describe('load caching', () => {
+    it('does not cache a rejected load and retries on the next call', async () => {
+      mockGet.mockRejectedValueOnce(new Error('transient KV error'));
+
+      // The first read hits the transient error and falls back to null.
+      const first = await asyncFeatureStore.get({ namespace: 'features' }, 'testFlag1');
+      expect(first).toBeNull();
+
+      // A later read must retry the provider (the beforeEach success impl) rather
+      // than reuse the cached rejected promise, and should succeed.
+      const second = await asyncFeatureStore.get({ namespace: 'features' }, 'testFlag1');
+      expect(second).toMatchObject(testData.flags.testFlag1);
+      expect(mockGet).toHaveBeenCalledTimes(2);
+    });
+
+    it('caches a successful load and reuses it across calls', async () => {
+      await asyncFeatureStore.get({ namespace: 'features' }, 'testFlag1');
+      await asyncFeatureStore.get({ namespace: 'segments' }, 'testSegment1');
+      await asyncFeatureStore.all({ namespace: 'features' });
+
+      expect(mockGet).toHaveBeenCalledTimes(1);
+    });
+  });
+
   describe('init & getDescription', () => {
     it('can initialize', (done) => {
       const cb = jest.fn(() => {

packages/sdk/fastly/src/api/EdgeFeatureStore.ts

@@ -32,7 +32,7 @@ export class EdgeFeatureStore implements LDFeatureStore {
    */
   private async _getKVData(): Promise<LDFeatureStoreDataStorage | null> {
     if (!this._deserializedPromise) {
-      this._deserializedPromise = (async (): Promise<LDFeatureStoreDataStorage | null> => {
+      const promise = (async (): Promise<LDFeatureStoreDataStorage | null> => {
         this._logger.debug('No cached data found, loading from KV store');
         const kvData = await this._edgeProvider.get(this._rootKey);
         if (!kvData) {
@@ -56,6 +56,20 @@ export class EdgeFeatureStore implements LDFeatureStore {
 
         return deserializedData;
       })();
+
+      // Do not cache a rejected load. If the KV read throws (for example a
+      // transient backend error), clear the cached promise so the next call
+      // retries instead of reusing the rejected promise for the rest of the
+      // request, which would make every flag evaluation fall back to defaults.
+      // A successful load that resolves to null (missing or undeserializable
+      // data) is still cached, since that is a stable state within a request.
+      promise.catch(() => {
+        if (this._deserializedPromise === promise) {
+          this._deserializedPromise = null;
+        }
+      });
+
+      this._deserializedPromise = promise;
     } else {
       this._logger.debug('Using cached deserialized data');
     }