tako: avoid panic when worker group is missing in multi-node solver

crates/tako/src/internal/scheduler/solver.rs

@@ -151,8 +151,7 @@ pub fn run_scheduling_solver_inner(
                     if worker.is_free()
                         && worker_groups
                             .get(&worker.configuration.group)
-                            .unwrap()
-                            .is_capable_to_run_rq(rq, now, worker_map)
+                            .is_some_and(|g| g.is_capable_to_run_rq(rq, now, worker_map))
                     {
                         set_placement_name(&mut solver, worker.id, batch.resource_rq_id, v_idx);
                         let v = create_mn_var(

crates/tako/src/internal/tests/test_query.rs

@@ -850,3 +850,29 @@ fn test_query_partial_absorbs_undeclared_demand_on_one_worker() {
     // On their own they are the probe of \S queries: exactly one worker, not none and not three.
     assert_eq!(ask(100, 0), 1);
 }
+
+#[test]
+fn test_query_multi_node_task_with_free_workers_before_scheduling() {
+    // Fake workers created by the query belong to groups that are not registered in the core.
+    // The solver must not panic when it considers them for a multi-node task.
+    let mut rt = TestEnv::new();
+    rt.new_workers_cpus(&[1, 1]);
+    rt.new_task(&TaskBuilder::new().n_nodes(2));
+
+    let r = compute_new_worker_query(
+        rt.core(),
+        &[WorkerTypeQuery {
+            partial: false,
+            descriptor: ResourceDescriptor::simple_cpus(1),
+            time_limit: None,
+            max_sn_workers: 2,
+            max_workers_per_allocation: 2,
+            min_utilization: 0.0,
+        }],
+    );
+    assert_eq!(r.single_node_workers_per_query, vec![0]);
+    assert_eq!(r.multi_node_allocations.len(), 1);
+    assert_eq!(r.multi_node_allocations[0].worker_type, 0);
+    assert_eq!(r.multi_node_allocations[0].worker_per_allocation, 2);
+    assert_eq!(r.multi_node_allocations[0].max_allocations, 1);
+}