Implements a 32-way trie persistent vector for O(1) lexical address lookup in environment frames. This general-purpose data structure provides efficient immutable access with good locality properties, featuring threshold gating to optimize for shallow recursion depths while eliminating O(depth) scaling for deeply nested environments. Demonstrates skill in persistent data structure design and practical performance trade-offs.

Contains an _IdentityCache class that uses epoch-based invalidation to automatically detect when cached values become stale due to object mutations. Instead of tracking individual mutations, it maintains a global epoch that increments on mutations, with cache entries storing the epoch when created. This clever pattern solves a common caching problem with minimal overhead and could be extracted for use in other systems requiring identity-based caching with automatic invalidation.