Review feedback: comment expansion.

nexus/src/app/mod.rs

@@ -81,6 +81,9 @@ pub(crate) const MAX_NICS_PER_INSTANCE: usize = 8;
 
 // XXX: Might want to recast as max *floating* IPs, we have at most one
 //      ephemeral (so bounded in saga by design).
+//      The value here is arbitrary, but we need *a* limit for the instance
+//      create saga to have a bounded DAG. We might want to only enforce
+//      this during instance create (rather than live attach) in future.
 pub(crate) const MAX_EXTERNAL_IPS_PER_INSTANCE: usize = 32;
 pub(crate) const MAX_EPHEMERAL_IPS_PER_INSTANCE: usize = 1;