serve: honor recipe.cluster when --cluster is auto (docker path parity with tmux)

src/docker/mod.rs

@@ -71,6 +71,13 @@ pub async fn serve(
     let mut recipe = load_recipe(recipe_name, &config.recipe_sources).await?;
     let rn = recipe.name.clone();
     let re = recipe.engine.clone();
+    // CLI `--cluster auto` (the default) falls back to the recipe's `cluster`
+    // field — same behavior as the tmux path.
+    let cluster_name = if cluster_name == "auto" {
+        recipe.cluster.clone().unwrap_or_else(|| "auto".to_string())
+    } else {
+        cluster_name.to_string()
+    };
     info!(
         "{}",
         fluent_i18n::t!("recipe-starting", { "name" => rn, "engine" => re, "backend" => recipe.distributed_backend.map_or("none".to_string(), |b| b.to_string()) })
@@ -133,14 +140,14 @@ pub async fn serve(
         crate::orchestrate::prepare_cluster_dry_run(
             config,
             &recipe_for_select,
-            cluster_name,
+            &cluster_name,
             node_name,
         )?
     } else {
         prepare_cluster(
             config,
             &recipe_for_select,
-            cluster_name,
+            &cluster_name,
             node_name,
             &PrepareRequest {
                 prober: &SshProber,