pin the declared closure once per rebuild and seed the marker from the running closure

hive-c0re/src/job_queue/tests.rs

@@ -1560,3 +1560,23 @@ fn a_rebuild_is_live_for_its_own_agent_only() {
     );
     assert!(!q.rebuild_live("bob"));
 }
+
+/// Agents whose running closure differs from the declaration are rebuilt in one
+/// sweep. Each rebuild's window holds a build slot, so `buildSlots` caps how
+/// many swap at once, however many agents the sweep rebuilds.
+#[test]
+fn a_sweep_of_rebuilds_holds_one_build_slot_per_agent_window() {
+    let q = JobQueue::new(1);
+    let agents: Vec<String> = ["alice", "bob", "carol"].map(str::to_owned).to_vec();
+    insert(&q, |builder| {
+        crate::workers::auto_update::boot_nodes(builder, &agents, Vec::new());
+    });
+    assert_eq!(
+        declared_resources_of_kind(&q, "agent_window")
+            .iter()
+            .filter(|r| r.contains(&Resource::BuildSlot))
+            .count(),
+        3,
+        "every window declares the build slot"
+    );
+}