chore(#2400): skip the prebuild warm-build when the container is down

hive-c0re/src/job_queue/model.rs

@@ -68,7 +68,10 @@ pub enum NodeKind {
     /// meta `sync_agents`, optional per-agent relock, then
     /// `lifecycle::prebuild_toplevel`. `relock = false` only for
     /// meta-update cascade rebuilds (re-locking would revert the bump
-    /// the cascade just committed).
+    /// the cascade just committed). The `prebuild_toplevel` warm is
+    /// skipped when the container is already down — it only exists to
+    /// shrink the swap's downtime, which a stopped agent doesn't need
+    /// (the sync + dir prep still run; `Swap` builds inline).
     Prebuild { relock: bool },
     /// `nixos-container update` profile-swap (requires the container
     /// stopped). Re-applies nspawn flags + resource limits first —