Skip dir-refresh cycle when transfer is active

Avoids competing with write-back uploads or read-cache fill I/O by
returning early if transfers > 0 or speed exceeds 10 KiB/s threshold.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/supervisor.rs

@@ -372,6 +372,23 @@ fn spawn_dir_refresh(
             interval,
         }
         .spawn(generation, gen_arc2, sd, move || {
+            // Skip this refresh cycle if the share is actively transferring.
+            // Avoids competing with write-back uploads or read-cache fill I/O.
+            {
+                let s = status.read().unwrap();
+                if let Some(ss) = s.shares.iter().find(|ss| ss.name == share_name) {
+                    if ss.transfers > 0 || ss.speed > SPEED_ACTIVE_THRESHOLD {
+                        tracing::info!(
+                            share = %share_name,
+                            transfers = ss.transfers,
+                            speed_bps = ss.speed as u64,
+                            "dir-refresh skipped: transfer active"
+                        );
+                        return Ok(());
+                    }
+                }
+            }
+
             // Enumerate top-level subdirectories by reading the FUSE mount point.
             // The VFS root itself is not a valid vfs/refresh target in rclone.
             let dirs: Vec<String> = std::fs::read_dir(&mount_point)