A by-name CONTEXT input edge (context :people): the node READS the target
as settled context but is NOT recomputed when the target changes. Still a
real input (validated, ordered by depth so the target settles first, read
at recompute) — it just doesn't propagate. For a node whose recompute is
expensive/non-deterministic and consults mutable context it shouldn't be
re-triggered by (an LLM step that looks up a human-curated
people/positions table). Contrast ref, which dirties this node on change.