analyze_impact could raise on a non-list target_node_ids from the LLM (no
isinstance guard, unlike fields/values) -- violated the never-crash
contract. Guard it the same way. Also collapse the fake models' invoke_llm
signatures to **_kwargs (underscore-prefixed, no noqa) per the ARG lint
constraint, and pin two more malformed-shape degrade paths
(build_edit_intents non-list intents, propose_edit_plan non-list plan).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>