Function base_map_hash 

pub fn base_map_hash(graph: &Graph, root: NodeId) -> u64

NodeId-independent content hash of the subgraph rooted at root.

Recursively hashes each node as (op identity, child hashes), folding in each child’s hash rather than its NodeId — so two independently-built graphs (different arenas, different NodeId numbering) that are structurally identical hash equal. Reuses this module’s existing canonicalization primitives rather than duplicating them:

• op_key for op identity when available (covers every primitive + Op::Fused variant CSE already relies on).
• is_commutative to sort child hashes for Add/Mul, so a + b and b + a hash equal (mirrors CSE’s own commutative-operand canonicalization). Maximum/Minimum are excluded – see GAP-271.

op_key deliberately excludes Op::Const (its payload lives in the graph’s storage_map slot, not the Op enum) and returns None for a handful of other ops (in-place, indexing, and anything else not explicitly listed). For those, this function falls back to (discriminant, shape, dtype) — and, for Op::Const specifically, additionally folds the constant’s real bytes when they’re readable (see fold_const_bytes below) so two independently-built recipes with equal constants hash equal, not just equal-shaped placeholders.

This is a cheap structural pre-filter for cross-graph recipe identity: structurally-equal-up-to-commutative-reordering-and-fusion-depth base maps hash equal. It does NOT canonicalize associativity or distributivity ((a + b) + c vs a + (b + c) hash differently) — a numeric verify pass covers that residual. Hashes are only stable within one process / DefaultHasher instance; never persist or compare them across processes.