LangGraph 1.2.11 puts `trace_policy` on `add_node`.

Per-node tracing declared in the graph rather than configured globally or wrapped by hand (GitHub), useful when one node handles PII or generates trace volume you don't want to store. Also a checkpoint fix for writes at plain-value seeds in delta channel history, and a cryptography bump from 48.0.1 to 50.0.0. Small release. Per-node trace control is the kind of primitive that only appears once a framework has production users with compliance people attached.