addressed PR feedback

Author: bachuv

exporthistory/src/main/java/com/microsoft/durabletask/exporthistory/activities/ExportInstanceHistoryActivity.java

@@ -53,6 +53,10 @@ public class ExportInstanceHistoryActivity implements TaskActivity {
     private final DurableTaskClient client;
     private final ExportHistoryStorageOptions storageOptions;
 
+    // Lazily initialized and cached to avoid rebuilding per invocation
+    private volatile BlobContainerClient cachedContainerClient;
+    private volatile String cachedContainerName;
+
     public ExportInstanceHistoryActivity(DurableTaskClient client, ExportHistoryStorageOptions storageOptions) {
         this.client = client;
         this.storageOptions = storageOptions;
@@ -150,11 +154,7 @@ private void uploadToBlob(
             ExportFormatKind kind,
             String instanceId) throws IOException {
 
-        BlobServiceClient serviceClient = new BlobServiceClientBuilder()
-                .connectionString(this.storageOptions.getConnectionString())
-                .buildClient();
-        BlobContainerClient containerClient = serviceClient.getBlobContainerClient(containerName);
-        containerClient.createIfNotExists();
+        BlobContainerClient containerClient = getOrCreateContainerClient(containerName);
 
         BlobClient blobClient = containerClient.getBlobClient(blobPath);
         Map<String, String> metadata = Collections.singletonMap("instanceId", instanceId);
@@ -185,4 +185,24 @@ private void uploadToBlob(
             blobClient.uploadWithResponse(uploadOptions, null, null);
         }
     }
+
+    private BlobContainerClient getOrCreateContainerClient(String containerName) {
+        // Double-checked locking: reuse the cached client if the container name matches
+        if (this.cachedContainerClient != null && containerName.equals(this.cachedContainerName)) {
+            return this.cachedContainerClient;
+        }
+        synchronized (this) {
+            if (this.cachedContainerClient != null && containerName.equals(this.cachedContainerName)) {
+                return this.cachedContainerClient;
+            }
+            BlobServiceClient serviceClient = new BlobServiceClientBuilder()
+                    .connectionString(this.storageOptions.getConnectionString())
+                    .buildClient();
+            BlobContainerClient containerClient = serviceClient.getBlobContainerClient(containerName);
+            containerClient.createIfNotExists();
+            this.cachedContainerName = containerName;
+            this.cachedContainerClient = containerClient;
+            return containerClient;
+        }
+    }
 }

exporthistory/src/main/java/com/microsoft/durabletask/exporthistory/client/DefaultExportHistoryJobClient.java

@@ -48,18 +48,21 @@ public void create(@Nonnull ExportJobCreationOptions options) {
             throw new IllegalArgumentException("options must not be null.");
         }
 
-        // Build options with destination from storage options if not set
-        ExportDestination destination = options.getDestination();
-        if (destination == null) {
-            String prefix = options.getMode().name().toLowerCase() + "-" + this.jobId + "/";
-            destination = new ExportDestination(
-                    this.storageOptions.getContainerName(),
-                    this.storageOptions.getPrefix() != null ? this.storageOptions.getPrefix() : prefix);
-        }
-
-        // Create options with resolved destination
+        // Resolve destination by independently falling back each field:
+        // prefix:    user destination → storageOptions → auto-generated per-job default
+        // container: user destination → storageOptions
+        String defaultPrefix = options.getMode().name().toLowerCase() + "-" + this.jobId + "/";
+        ExportDestination userDest = options.getDestination();
+        String prefix = userDest != null && userDest.getPrefix() != null ? userDest.getPrefix()
+                : this.storageOptions.getPrefix() != null ? this.storageOptions.getPrefix()
+                : defaultPrefix;
+        String container = userDest != null && userDest.getContainer() != null ? userDest.getContainer()
+                : this.storageOptions.getContainerName();
+        ExportDestination destination = new ExportDestination(container, prefix);
+
+        // Create options with resolved destination, always using this client's bound jobId
         ExportJobCreationOptions resolvedOptions = new ExportJobCreationOptions(
-                options.getJobId(),
+                this.jobId,
                 options.getMode(),
                 options.getCompletedTimeFrom(),
                 options.getCompletedTimeTo(),

exporthistory/src/main/java/com/microsoft/durabletask/exporthistory/client/ExportJobQueryPageable.java

@@ -80,7 +80,6 @@ public Iterable<ExportJobQueryResult> byPage() {
         return () -> new Iterator<ExportJobQueryResult>() {
             private String continuationToken = baseQuery != null ? baseQuery.getContinuationToken() : null;
             private boolean hasMorePages = true;
-            private boolean firstPage = true;
 
             @Override
             public boolean hasNext() {
@@ -103,7 +102,6 @@ public ExportJobQueryResult next() {
                 ExportJobQueryResult result = queryExecutor.apply(query);
                 this.continuationToken = result.getContinuationToken();
                 this.hasMorePages = this.continuationToken != null && !this.continuationToken.isEmpty();
-                this.firstPage = false;
                 return result;
             }
         };