fix: nightly rustfmt import ordering in parquet_merge_pipeline

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: g-talbot

quickwit/quickwit-indexing/src/actors/metrics_pipeline/parquet_merge_pipeline.rs

@@ -41,6 +41,7 @@ use quickwit_common::temp_dir::TempDirectory;
 use quickwit_parquet_engine::merge::policy::ParquetMergePolicy;
 use quickwit_parquet_engine::split::ParquetSplitMetadata;
 use quickwit_proto::metastore::MetastoreServiceClient;
+use quickwit_storage::Storage;
 use tokio::sync::Semaphore;
 use tracing::{debug, error, info, instrument};
 
@@ -51,7 +52,6 @@ use super::{METRICS_PUBLISHER_NAME, ParquetUploader};
 use crate::actors::pipeline_shared::wait_duration_before_retry;
 use crate::actors::publisher::DisconnectMergePlanner;
 use crate::actors::{MergeSchedulerService, Publisher, Sequencer, UploaderType};
-use quickwit_storage::Storage;
 
 /// Spawning a merge pipeline puts pressure on the metastore, so we limit
 /// concurrent spawns (shared with Tantivy merge pipelines).
@@ -227,9 +227,12 @@ impl ParquetMergePipeline {
 
         let immature_splits = self.initial_immature_splits_opt.take().unwrap_or_default();
 
-        // Spawn actors bottom-up so downstream mailboxes are available.
+        // Spawn actors bottom-up: each actor's constructor needs a mailbox
+        // for the actor below it in the chain, so we start from the publisher
+        // (bottom) and work up to the planner (top).
 
-        // 1. Merge publisher
+        // 1. Merge publisher — publishes merged splits to the metastore and
+        //    feeds back ParquetNewSplits to the planner for further merging.
         let merge_publisher = Publisher::new(
             METRICS_PUBLISHER_NAME,
             QueueCapacity::Unbounded,
@@ -244,7 +247,8 @@ impl ParquetMergePipeline {
             .set_kill_switch(self.kill_switch.clone())
             .spawn(merge_publisher);
 
-        // 2. Sequencer (preserves publish ordering)
+        // 2. Sequencer — ensures merged splits are published in the order
+        //    they were uploaded, even if uploads complete out of order.
         let sequencer = Sequencer::new(merge_publisher_mailbox.clone());
         let (sequencer_mailbox, _sequencer_handle) = ctx
             .spawn_actor()