Fix redis NOGROUP errors when running samples

Running the samples that use redis where workers are separate generates non-stop errors
like the following:

2025/09/15 23:01:02 ERROR error polling task error="dequeueing task: NOGROUP No such key 'task-stream:system:activities' or consumer group 'task-workers' in XREADGROUP with GROUP option"

The original error occurred because:

* The worker tries to recover abandoned tasks during startup using XAUTOCLAIM
* This requires existing consumer groups for the Redis streams
* Previously, consumer groups were only created when PrepareWorkflowQueues/PrepareActivityQueues were explicitly called
* The recovery operations happened before queue preparation, causing NOGROUP errors

The fix ensures that consumer groups for the essential queues (default and _system_) are created automatically during Redis backend initialization, eliminating the race condition.

Author: jwilder

backend/redis/redis.go

@@ -86,6 +86,11 @@ func NewRedisBackend(client redis.UniversalClient, opts ...RedisBackendOption) (
 		return nil, fmt.Errorf("loading Lua scripts: %w", err)
 	}
 
+	// Ensure default consumer groups exist to prevent NOGROUP errors during startup
+	if err := rb.ensureDefaultConsumerGroups(ctx); err != nil {
+		return nil, fmt.Errorf("ensuring default consumer groups: %w", err)
+	}
+
 	return rb, nil
 }
 
@@ -149,3 +154,22 @@ func (rb *redisBackend) FeatureSupported(feature backend.Feature) bool {
 
 	return true
 }
+
+// ensureDefaultConsumerGroups creates the consumer groups for the default and system queues
+// to prevent NOGROUP errors when the worker starts and tries to recover abandoned tasks
+func (rb *redisBackend) ensureDefaultConsumerGroups(ctx context.Context) error {
+	// Initialize consumer groups for both default and system queues
+	queues := []workflow.Queue{workflow.QueueDefault, core.QueueSystem}
+
+	// Prepare workflow queue consumer groups
+	if err := rb.workflowQueue.Prepare(ctx, rb.rdb, queues); err != nil {
+		return fmt.Errorf("preparing workflow queue consumer groups: %w", err)
+	}
+
+	// Prepare activity queue consumer groups
+	if err := rb.activityQueue.Prepare(ctx, rb.rdb, queues); err != nil {
+		return fmt.Errorf("preparing activity queue consumer groups: %w", err)
+	}
+
+	return nil
+}