Send node_ids from dashboard, error on RDMA when unavailable

Dashboard was not including the user's node filter in the POST to
/meta_instance, so placement ignored which nodes the user selected.
Also, placement silently fell back to Ring when RDMA was requested but
no RDMA-connected cycles were available — now raises an error that
surfaces via MetaInstancePlacementFailed.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

dashboard/src/routes/+page.svelte

@@ -644,6 +644,7 @@
           sharding: preview?.sharding ?? selectedSharding,
           instance_meta: preview?.instance_meta ?? selectedInstanceType,
           min_nodes: selectedMinNodes,
+          node_ids: nodeFilter.size > 0 ? Array.from(nodeFilter) : undefined,
         }),
       });
 

src/exo/master/placement.py

@@ -106,7 +106,11 @@ def place_instance(
         cycle for cycle in smallest_cycles if topology.is_rdma_cycle(cycle)
     ]
 
-    if command.instance_meta == InstanceMeta.MlxJaccl and smallest_rdma_cycles != []:
+    if command.instance_meta == InstanceMeta.MlxJaccl:
+        if not smallest_rdma_cycles:
+            raise ValueError(
+                "Requested RDMA (MlxJaccl) but no RDMA-connected cycles available"
+            )
         smallest_cycles = smallest_rdma_cycles
 
     cycles_with_leaf_nodes: list[Cycle] = [