- Graph definitions (v3, v4) now declare MODELS mapping role → model string - engine.py extracts MODELS and applies to nodes during instantiation - frame_engine.process_message() accepts model_overrides for per-request swaps (restored via try/finally after processing) - 11/11 engine tests green Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>