Computes a node's topology signature: a hash of its plugin name plus the sorted
(multiset) signatures of its anchor-tree children. Status and join edges are excluded,
so isomorphic fan-out branches share a signature regardless of order or run state.
Memoized by instance ID; the anchor tree is acyclic (single parent), so recursion
terminates in O(n) across a feed.
Computes a node's topology signature: a hash of its plugin name plus the sorted (multiset) signatures of its anchor-tree children. Status and join edges are excluded, so isomorphic fan-out branches share a signature regardless of order or run state.
Memoized by instance ID; the anchor tree is acyclic (single parent), so recursion terminates in O(n) across a feed.